How to build a better speed limit

Sometime in November, Texas will open a stretch of toll road south of Austin where the speed limit will be 85 miles per hour.It will be the highest speed limit in America. (Montana used to have no speed limit at all during the day, but that changed in 1999.)

Naturally, one of the big arguments against this is that higher speeds lead to more accidents. And there is some data to back this up. For instance, the Insurance Institute for Highway Safety makes a pretty good case for lower speed limits in a Q&A posted on their site:

In 2010, a total of 10,395 deaths, or nearly a third of all motor vehicle fatalities, occurred in speed-related crashes. Based on a nationally representative sample of police-reported crashes, speeding – defined as exceeding the speed limit, driving too fast for conditions or racing – was involved in 16 percent of property-damage-only crashes and 20 percent of crashes with injuries or fatalities. The National Highway Traffic Safety Administration (NHTSA) estimates that the economic cost of speed-related crashes is more than $40 billion each year.

...The National Research Council attributed 4,000 fewer fatalities to the decreased speeds in 1974 compared with 1973...

A 2009 study examining the long-term effects of the 1995 repeal of the national speed limit found a 3 percent increase in road fatalities attributable to higher speed limits on all road types, with the highest increase of 9 percent on rural interstates. The authors estimated that 12,545 deaths were attributed to increases in speed limits across the U.S. between 1995 and 2005.

There is definitely a relationship between speed and safety. It's there consistently in individual studies and you see it when you start looking at lots of studies all at once, too. But the meta-analyses—research that compares and analyzes the results of many studies—also show that the speed/safety connection is probably more complicated than it first appears. Speed limits matter. But maybe we need more options to pick from than a simple, static "faster" or "slower".

People and the environment both have a big impact on the relationship between speed and safety. There are a couple of meta-analyses available to read for free online. Check them out, and you'll see how psychology and road conditions play a big role.

For instance, a 1998 publication from the Federal Highway Administration found that the type of road matters. If you raise the speed limit on a road where people are already driving slowly, it won't affect safety at all.

In general, changing speed limits on low and moderate speed roads appears to have little or no effect on speed and thus little or no effect on crashes. This suggests that drivers travel at speeds they feel are reasonable and safe for the road and traffic regardless of the posted limit. However, on freeways and other high–speed roads, speed limit increases generally lead to higher speeds and crashes.

Here's another weird fact that turns up in both the 1998 report and a paper published by the Transportation Research Board in 2001: You're actually safest when you're traveling with the speed of the traffic around you. Speed-related accidents tend to happen when people are traveling faster or slower than the other cars on the road.

In fact, the 1998 report says that most speed-related accidents happen because an individual is driving too fast for the conditions of the road—that's the current weather, the width of the specific road, and how fast other people are driving.

The conclusion that both reports come to: We don't necessarily need lower speed limits. What we need are speed limits that adjust to the current conditions and the specific needs of a specific road. A variable speed limit would reflect the reality that a lot of drivers already see and respond to, and it might be more easily accepted by the drivers who ignore one-size-fits-all speed limits today. Plus, the variable speed limit would allow the law to match up with what's actually safe. If traffic is flowing at an average of 60 mph, it doesn't make sense to have 70 mph posted—somebody is going to try to keep up with the speed limit and create an unsafe condition.

It's an interesting idea. So far, there's not a lot of good data available to show whether or not it actually reduces accidents and fatalities. Variable speed limits have been tested out around the world, but they remain rare and, in North America, are mostly relegated to stretches of rural highway in places with a history of extreme weather—for instance, a road in Tennessee that gets a lot of heavy fog.

But the basic story is that we need more data. To know whether or not variable speed limits actually make sense, we need them to be implemented in more places with more traffic.

Synthesis of Studies on Speed and Safety - 2001 meta-analysis
Synthesis of Safety Research Related to Speed and Speed Management - 1998 meta-analysis
Driving Speed and the Risk of Road Crashes, A Review - 2006 meta-analysis that is behind a paywall
Wikipedia on variable speed limits
US Federal Highway Administration research on variable speed limits in construction zones

Image: Driving Cars in a Traffic Jam, a Creative Commons Attribution (2.0) image from epsos's photostream

Image: Speed Limit 35, a Creative Commons Attribution (2.0) image from 71966930@N00's photostream


  1. Please delete this comment after Maggie sees it: the word “data” is plural. Reading/hearing “data is” is really jarring and distracting for people who have spent much time studying science. We’ve just about gotten used to computer people writing/talking that way, but we still hope science reporters/writers get it right. Also, while I’m ranting, scientific names of things have the following correct format: Genus species: Homo sapiens. Often we see correct formatting at the linked entry, but the format has been change to the incorrect form at boingboing.

    1. As a Latin word, “data” is definitely plural; but in English, treating it in some contexts as a mass noun (i.e. behaving grammatically like “sand” or “water”) is almost old as the adoption of the word itself.  (The OED [paywalled] dates this usage to 1702; for a rough-and-ready comparison, see Google n-grams.)  There’s nothing either new or wrong about it.

      My personal take on it: when talking about a small, discrete set of facts — when one might reasonably talk about a single datum — I think of data as a plural count noun.  When talking about a set of facts so big or so tightly-knit that one couldn’t meaningfully count it, I think of data as a mass noun.  Most technical usage seems to fit this distinction.

      (I’m with you on the issue of Linnaean names, though. It’s a useful and meaningful distinction, and pretty consistently observed in technical publishing.)

      1. Your n-gram link is pretty cool, and it helps explain my sensitivity to “data is”: I was in graduate school during and just after the golden age of “data are”, watching in alarm as “data is” grew in popularity.

        I note that the rise of “data is” correlates with growth of computer industry, where I see the usage most commonly.

        I promise to try to get over associating “data is”  with poor (non-computer) science literacy.

    2. Please delete this comment after Maggie sees it

      Why on earth would I want to get rid of evidence of your pedantry?

    3. Ironically enough, I think that you mean “the format has been changed to the incorrect form at boingboing”

  2. If you drive 65 MPH on a rainy, foggy day with lots of traffic, cops won’t mind a bit.

    But if you see a long, straight stretch of completely empty highway on a dry, sunny day? You may as well save the cops the trouble and just tear up your license then and there.

  3. Speed is NOT the problem. It’s the IDIOTS BEHIND THE WHEEL!

    Seriously, barring the odd surprise catastrophic mechanical failure, people just need to pay attention and there would be no crashes.

    1. people just need to pay attention and there would be no crashes.

      Thanks for the belly-laugh to start off the weekend!

    2. Human beings systematically overestimate their competence.  Speed makes the consequences of these sorts of errors more significant.  Speed is part of the problem, idiots are part of the problem, and “paying attention” is not a sufficient solution.

      1. Would you agree that speed is only part of the problem if the partipants aren’t “paying attention”? 

    3. So speed limits are for idiots?  And smart people like you should be allowed to drive however you want?

      Seems legit.

      1. So…you’re suggesting that we just ditch the driving test that you take in order to get a license in favor of lowering the speed limit until accidents become meaningless? Because currently, we do decide if we as a society think that individuals are smart enough to drive based on the current rules.

      2. Well, I never said speed limits are for idiots. 

        I’m sure the limits were agreed upon due to a presentation of statistical bullshit that the DOT (or whomever had the idea of what speed limits should be set to, NHTSA?) made pretty charts to show what speed limits should be. 

        People should drive in a way that works with the traffic around them. If driver A-F is going 70mph, and driver G is going 55 (posted limit) it causes a disruption in the mass of tons of bricks rolling down the road. Sadly, driver G thinks they should only do the posted limit.

        And by Antinous not disagreeing with me counts for something! Huzzah! :D

    4. 80% of drivers believe that they are above average drivers. This is why there are so many idiots behind the wheel.

  4. It’s just as bad to have a posted speed limit of 50 if most drivers ignore it and do 65. One person stubbornly ignoring conditions and staying below the aggregate speed can be as or more dangerous as someone speeding past.

    1. Exactly. Those people are a hazard to everyone around them! Go with the flow maaaaaan!

      My wife is one of those people, and I can’t get her to stop doing it :(  I don’t let her drive if i’m in the car.

      1. And it’s worse when they’re in the far left lane despite signs stating “slower traffic keep right.” I guess they think going the speed limit is as fast as anyone should be going, therefore they don’t consider themselves “slower traffic…?”

        That causes people in the left lane who want to go faster to have to pass on the right in the middle lane or right lane, depending on how many lanes there are, which increases chances of accidents since slower traffic uses those lanes for passing or merging at slower speeds.

          1. Issac: That’s the law in quite a few places, but enforcement is mostly absent. I’ve never seen someone pulled over for camping in the left lane, or for going too slow, even though these behaviors are dangerous.

          2. John: it did happen in Toronto on the 401. Context: the 401 is a 12 lane freeway with a posted speed of 100 km/h, (62 mph) but a traveling speed of 130 to 140 (81-87) in the fast lane.

            One guy got a speeding ticket for doing 130 in the merge lane, got mad and started doing 100 in the fast lane. He got a ticket for obstructing traffic, contested the ticket, and lost.

          3. In the Toronto example below, they should just raise the limit to 120kph and call it a day. Then actually enforce that speed. The 100kph limit is laughable, as it is not enforced.

            Honestly most speed limits, not in city driving around schools and hosipitals etc… on the main highways have ZERO to do with “safety”. I think you would be hard pressed to actually conclusive data in that regard.

            Speed limits of that kind are about fuel economy, and using less fuel as a nation. Which isn’t really a bad thing really.

            Accidents are caused by bad drivers, who are not always the same as fast drivers. Of course speeding those bad drivers up, won’t help matters either.

            In many cases speeding tickets are now nothing more than a device to generate revenue. Speed cameras are a great example of this. “Training” courses to reduce fine where the money goes locally rather than into public coffers is another great example.

            “Would be a shame to give you this large ticket. Sumpthing might happen to your licence. But seein’ as we’re bein’ nice today, if you take this 100$ course and pass (everyone does) then no ones the wiser see… Oh just make the check out to cash…thanks boyo!”

          4. Ryan:  you’re mostly right.   But note that they do (rightly) give tickets for going 120 km/h in the feeders or the merge lanes.   So they can’t raise the speed limit to 120 km/h.   Really, they should have 4 different speed limits:  different speeds are appropriate for the feeder lanes, the merge lanes, the inner lanes and the fast lanes.  But they can’t do that, so they have to set the speed limit for all lanes to a speed that is appropriate for the merging lanes, not to a speed that’s appropriate for the fast lane.

        1. In some jurisdictions, “slower traffic” means traffic that is both slower than other traffic and slower than the speed limit, thus the logic you provide may be legal, even if it isn’t safe.

    2. Unfortunately that’s the law. I know someone who got his 3rd speeding ticket for going the same speed as everyone else (65mph) in a 50mph zone. His insurance premiums are now $7k a year and 1 more point and he loses his license.

      So FU. I’m going to speed limit. I’m not going to pay $7k a year just so you can feel good breaking the law. Slow the F down!

      1. Total agreement here.

        I won’t say every officer will do it, but there are plenty who really don’t like the “but everyone else was speeding” argument.  You got stopped for breaking the law.  If everyone else was looting, shooting, raping, etc., is “everyone else was doing it” a valid alibi?  No.

        I’ve gotten stopped only twice in my life, when I let my guard down. Where I live, there’s getting to be more people, speed limits are dropping, but paradoxically it’s a lot of urban folks moving to a rural area.  (“Your corn is blocking the view!  You have to do something about the corn!”)  Nobody wants to drive speed limit.  Look, I know it’s stupid to drive 30mph on a country road going through a bean field, but every time I drive over speed limit I see a police officer, I don’t have the extra money to spend on a ticket or insurance, I think I’ll just drive speed limit.

        1. The correct argument is “I was speed matching the rest of traffic for safety. I just read on Boing Boing the other day that this is the best way to avoid an accident.”

        1. It only takes 3 speeding tickets to get 3 points, 1 point per ticket. 4 points = no license. 3 points = $7k a year in premiums. 

          Going 65 in a 50mph zone vs 80 in a 65mph zone is no different. Both are speeding.The people above who think “Everyone else is going 65 in a 50mph zone so I should too” need to slow down and not the other way around.

          1. From the article: “You’re actually safest when you’re traveling with the speed of the traffic around you.”
            Your proposed solution would make me less safe. I would prefer to be alive rather than right.

  5. “speeding – defined as exceeding the speed limit, driving too fast for conditions or racing” I wonder what the statistics would be if you eliminated the last 2 items, which are definitely dangerous and only kept merely “exceeding the speed limit.”  

    A careful and experienced driver, simply going 75 in a 65 zone on a sunny day with no traffic on a straight road is not the same as kids racing or driving 75 in the rain at night. I would think that long, straight, flat roads like in many states should be fine to go 85 in the daytime in good weather.

    1. I thought the exact same thing as I read that definition.  In general, our current system of speed limits and enforcement has zero to do with safety and everything to do with cops filling quotas.  If they set realistic speed limits on freeways, and then enforced them strictly, I’d be much more okay with that.

      1. What’s unrealistic about 65 mph?  You realize pretty much no human being ever traveled that fast until the 20th century, right?

        Remember that doubling the speed quadruples the damage done in any subsequent accident.  If there is some non-zero probability of accidents under any conditions, increasing speed limits would increase death, injury, and property damage due to accidents.

        1. What’s unrealistic about 65 mph?

          If your IP tracks correctly…well first of all, condolences…and second, you live in a densely populated area where everything is very close to everything else. Out here in California, folks sometimes live 30 miles from the nearest grocery store.

          1. If your IP tracks correctly…


            …well first of all, condolences…

            …and mean. 

            Have fun with my IP address, since apparently you’re checking up on these things.

        2. The problem with 65 (or any limit) is that many people are perfectly capable of driving SAFELY at significantly faster speeds.  It is unnecessary and inefficient to slow down competent drivers just for the sake of incompetent drivers.  

          Just as gifted students are allowed to test out of introductory classes, skilled drivers should be allowed to test out of speed limits.  I can drive perfectly safely at 100, and by FSM I should be allowed to.  Far too much of society revolves around catering to the lowest common denominator.

          1. Congratulations!! You are in that elite group, who are always the exception to the rule. I suppose you can also safely text while driving? Well of course you can…

          2.  No.
            As a matter of fact, people can’t drive “perfectly safely” at all. That would mean that you could absolutely guarantee that you would never have an accident- and of course you can’t. You may think you can, but it’s not the case.
            Driving is an activity where the slightest tenth-of-a-second lapse of concentration, or even briefly paying attention to the wrong thing, can lead to accident. Human beings cannot bring to bear the necessary concentration, 360-degree vision, and sub-millisecond reaction times necessary to drive “perfectly safely”.

        3. By that reasoning, all highways should have 30 mph speed limits, because a) no one pre-car traveled that fast and b) it would quarter the damage.

      2. In my area of the country, The San Francisco Bay Area, it has nothing to do with quotas. If it did they cops would hang out in the 50mph zone between Treasure Island and Candlestick Park that 95% of the traffic does not obey. They’d make bank and yet I rarely see anyone pulled over.

        Apparently in Washington state they do enforce the speed limit more strictly so maybe the quota thing fits that state.

        1. cops would hang out in the 50mph zone between Treasure Island and Candlestick Park

          Nah. They hang out on Laguna Honda and catch people speeding around the curves.

        2.  Try speeding on one of Washington’s Indian reservations.  The tribal officer will spot you, and as the old saying goes. “your a$$ is grass and I’m a mowing machine.”

  6. A few notes: 
    The studies quoted note the accidents caused by “exceeding the speed limit or driving too fast for conditions”. That doesn’t necessarily mean that they were traveling above 65mph. “too fast for conditions” can be 25mph on a curvy, rainy road, and “exceeding the speed limit” can be 40 in a 35. Also, you can get a speeding ticket for driving too fast for conditions if you are driving slower than the posted limit, but conditions dictate you should be traveling slower, like a rainstorm, blizzard or with ice on the road.

    There is a stretch of Highway in Utah that is currently 85 mph, but I believe it is only experimental. 
    I believe that inconsistency is part of our problem speed limits vary so widely on the same stretch of highway or through different parts of the country that I believe many drivers are only vaguely aware of the posted speed limit. we need a tiered/color-coded  speed limit system.

    Freeway Speed
    Highway Speeds
    City Speeds
    Residential Speeds
    with plus or minus modifiers for dangerous curves and or slippery conditions.

      1.  They’re also REALLY goddam expensive.  Like $350.00 Per sign or more.  The thing is, these kinds of signs cost about $80.00 to make, but you know, the government will buy anything at any price, and chalk the inflation up to supporting local business.

        1. The sign might cost $80.00 to make, but then someone needs to install it. Factor in a profit margin for the manufacturer, transport to the site and the cost of a few road workers to install it and $350 starts seeming more reasonable.

      2. I have a lot less sympathy for people who speed on surface streets, because there are more speed interruptions than there are on most highways  (deer, children, wet leaves, joggers, driveways, turning cars, etc.).  
        That said: I agree: if you want me to follow the rules, tell me what they are. My city has ‘default’ speed limits for residential areas and commercial areas, which one can look up in the city code, but few people have the resources to do that.

  7. Lane Discipline.  I just drove home from work doing 135mph (Germany).  Yeah they have alot of spectacular accidents here, but there is potential for so much worse.  The reason it is not carnage on the autobahn is because people are much more likely to follow the rules, most notably slower traffic keep right and no passing on the right.     When I’m back in the US it drives me absolutely nuts when people merge as fast as possible into the lane second from the left (doesn’t matter how many lanes in total there are, always second from left), set cruise control for speed limit + 5mph and then shut off their brain. 

    Maybe it’s that wild card of  having very very fast drivers that keeps people alert here.

    1. If only I lived in the part of the US you are talking about! Where I live, 50% of the drivers hang out in the far left lane for no reason, and they treat it like a roller-coaster: 50mph uphill, 70mph downhill. About 1% actually know how to drive. The other 49% just do the stupid roller-coaster thing, making it so that you can have a 5-lane highway of all loose traffic totally blocked by a line of cars all changing speed as they ascend and descend hills. F***ing idiots.

    2. Same for Italy. They drive very fast and aggressively, but they are ALWAYS paying close attention to what they are doing. I think it’s a wash as far as the number of accidents goes if you compare Italy to the U.S. The main difference is that you feel more in control there and you can get where you are going more quickly.
      I always thought it was a combination of inattentive driving and speed differentials that causes most accidents.

    3.  In Germany drivers have to be able to handle the car at speed in order to get a license.  Also, a fast-lane squatter will get pulled over and will receive a painful fine. 

      Drivers’ Ed here focuses on parallel parking; in Germany it focuses on performance driving.  Also, we don’t invest enough in highway maintenance to make the higher speed limits feasible.

      1. Yeah, with the road buckling we saw in MN and WI this summer, 135 mph would have sent you into the stratosphere!

    4. “…it drives me absolutely nuts when people merge as fast as possible into the lane second from the left …, set cruise control for speed limit + 5mph and then shut off their brain.”

      I understand where you’re coming from but that’s actually not so bad considering all the other things people do that are more dangerous.  Slaloming around other cars while maintaining a speed 20mph in excess of the average flow comes to mind.  Squatting in the left lane at exactly the limit is worse, too. 

      Frankly, I’d be generally (not perfectly, just generally) happier if people would pick a lane, pick a speed, and maintain them both.  It’s not ideal but it’s a lot better than much of the asshattery I see on the road.

    5. As someone who’s passed tests in more than one country I’ll add that driver skill is directly related to test difficulty. The US test is comparatively easy and in many places people can drive very young. In California you don’t have to demonstrate any ability to handle a care at speed, in less than perfect conditions, or do any challenging maneuvers. In countries where the test is harder, or in multiple parts over time, drivers are better overall. 

      In the UK the size and power of the motorcycle you can ride is limited by the tests you’ve taken (or it was when I was there). As you want to ride a larger bike you have to get re-tested. If cars were graded the same way we’d all be better off. You could then only legally drive a really fast/powerful car if you’d been tested as able to manage it at speed.If tests were set up this way, fewer people would be legally able to drive fast and we’d all be safer. I suspect it would be popular after a fashion. The bragging rights would add to the exclusivity.

      1. It’s almost impossible NOT to get a license in California. You just show up every day until you accidentally pass.

  8. And old AI prof of mine, Dr. John Placer (then at Northern Arizona, currently at East Carolina), was involved in some research on variable speed-limit systems.  A quick search turns up some of the docs he put together:

    Fuzzy Variable Speed Limit Device Modification and Testing, Phase II
    Design and Implementation of a VSL System

    He discusses it a bit on his own faculty page:

    Three phases of a joint variable speed limit (VSL) research project have been completed. This project was a collaborative effort between Northern Arizona University (NAU) and the Arizona Department of Transportation (ADOT). In the first phase we developed and implemented a fuzzy algorithm that monitors real-time weather and road surface information and that continuously outputs speed limits appropriate to these conditions. In Phase II of the project, we upgraded and added new sensing and communications equipment to our test site on Interstate 40. This test site is a road and weather information  (RWIS) site. Phase III produced a detailed legal analysis of liability issues the state of Arizona would face if VSL systems are deployed in Arizona. The legal report was examined by the Arizona Attorney General’s (AG) office. The Arizona Department of Transportation, the Arizona Attorney General’s Office, and I are all in agreement that two major issues advise against deployment of automated variable speed limit systems in Arizona at this time. The first issue involves legal and liability issues the state faces and the second issue relates to a lack of state resources to adequately maintain the road and weather information stations that are required to operate VSL systems. Consequently, the VSL research project has been suspended pending possible changes related to these legal and resource issues. (For a recent publication refer to John Placer and A. Sagahyroon , Design and Implementation of a VSL System , Intelligent Automation and Soft Computing, 13, 2, 2007, pp.197-210.)

  9. I think variable speed  limits are a cool idea, but I would be concerned about speed creep. I notice that the flow-of-traffic is often about 10km/hr above posted speed limits. I think that over the long term people will take variable limits more seriously, but in the short term it could cause the flow-of-traffic to increase to unsafe speeds due to the unconscious tendency of people to drive faster-than, but not excessively so, beyond the posted limit. 

    1. Or the reverse.

      Every time I see a “WARNING: PHOTO ENFORCEMENT” sign on the freeway, traffic drops to 5 mph below the speed limit.  From 10 mph above it.  I believe this to be monumentally unsafe.  I fear that variable speed limits would produce similar results.

      I think there’s also a danger to having motorists unsure what the speed limit is in a given area.  I can generally predict that residential driving will be 25 mph, surface streets 35-45, freeways in town 55-65, and outside the city limits 75.  Introducing unpredictability into the system can cause, well, unpredictability.

      Then again, so can rain.  I live in Phoenix metro; we have dangerously stupid drivers who become more dangerous and stupid anytime water starts falling out of the sky.  (Head up north where it snows and they get even still stupider.)

      I still think it’s a fascinating project and there’s bound to be a way to take all those factors into account and perform a solid risk assessment on when to drop the limit and when to leave it as-is.

      1. “Every time I see a “WARNING: PHOTO ENFORCEMENT” sign on the freeway, traffic drops to 5 mph below the speed limit.  From 10 mph above it.  I believe this to be monumentally unsafe.”

        The thing that makes it unsafe are the douchebags who lane-jockey to go 2mph faster than everyone else (only to, on average, end up going slower than everyone else.)

  10. There must be a spike of accidents, fatalities, etc, occurring on holiday weekends, that inflate the numbers.

    On a car visit to Northern California several years ago, I miscalculated the dates and ended up on the I-5 South from SF to LA on Memorial Day Weekend Friday evening.

    There were only two types of driving conditions:
    1) Three separate hour-long traffic jams because up ahead 3 to 5 cars had annihilated themselves Autobahn-style.  In one of them, a semi-truck had been ripped in half.
    2) Sheer terror, cars packed like sardines at 80-85 mph.  Apparently the one-dimensional mass of humanity behind the wheels learned NO lessons from the carnages they’d just witnessed.

    First chance I got, I took a back road to Bakersfield, found a hotel, then resumed my trip next morning.  Things were much quieter and safer on the I-5 by then.

    BTW, I encountered no traffic once I took the rural road.  Everybody else, and I mean EVERYBODY, seemed to be in a hurry to “get there (wherever the hell that was) or die”.  That type of mediocre holiday mindlessness must raise the yearly average of accidents.  Yeah, I’m still scarred, angry and disappointed at humanity for that evening in 2006.

  11. “Naturally, one of the big arguments against this is that higher speeds lead to more accidents.”

    Actually, the vast majority of studies show that the number of accidents neither increase nor decrease with speed limit changes. (for instance: ). Your example text doesn’t even mention any changes in the rate of accidents.

    What does change is the severity of crashes. Fatalities will likely increase, but the number of accidents is unlikely to change.

    1. I remember one study that showed that reducing the speed limit reduced accidents, and increasing the speed limit also reduced accidents, at least in the short term.  Either action appeared to have the effect of making drives focus better until they became accustomed to the different speed limit.

  12. Going faster or slower than the designed speed limit (given the conditions) of any road, be it highway or gravel, is dangerous.

    1. “Designed” speed limits, as you imagine them, assume uniform characteristics of the cars. I own a car that can go 90MPH through bends that would crash a Yaris.

    2.  …and this is why there are lots (speaking anecdotally)  of accidents on the Arroyo Seco Parkway portion of the 110 Freeway.  This is the oldest freeway in Los Angeles, and was designed for a top speed of 45 mph.  Add in plenty of yahoos who think that going 75 is just about right, and heavy commute-time traffic, and you have accidents on an almost daily basis.

      1. That stretch is either a hoot or a nightmare, depending on my existential mood.  It feels like driving in Disneyland’s Autopia without the rails.  The offramps are comically designated with a 5 MPH speed limit.  Yes, five miles per hour, since they’re essentially 90 degree turns with something like a forty-foot radius… and the onramps are no better.  Can you get from a standing start to freeway speed in 50 yards or less?  You’d better!

        I used to avoid that stretch of the 110 like the plague, but now that I actually live in Pasadena, it occasionally turns out to be the best route for me to take, so I do.  It’s pretty fun if one stays out of the right lane and sticks close to the speed limit.  But man, you gotta pay attention.

  13. It would be nice if they came up with a slightly smarter system of regulating traffic when conditions/time/congestion are more ideal for faster driving.  Basically reverse-gridlock. 

    I’m also guessing that the antiquated 55MPH limit set a while back hasn’t taken into account any of the performance advances in modern cars – better braking, handling and control.

    1. I believe the 55 mph limit was established as an energy savings measure, not as a safety measure. Which is wild to think about, especially in connection to gas prices and energy policy today. Can you imagine the public response if a law maker today proposed lowering the national speed limit in order to save energy?

        1. It was kept after the embargoes ended for safety reasons, though there have been arguments since then about whether the 55 mph limit was noticeably safer.  Depends on who you ask. The Cato Institute, predictably, says that higher speed limits don’t hurt anybody.

          I don’t think today’s drivers are safer than the drivers of yesteryear, by and large, but the cars certainly are.  The tires, brakes, suspension and steering components, and gearing are all far better suited to higher-speed driving than they were forty years ago.  Doin’ the “double nickel” in one’s Olds Vista Cruiser or VW microbus was a good idea back in the day, not only to minimize fuel consumption (which wasn’t a heavy consideration when it cost two bits per gallon, but became more urgent during the OPEC embargoes of ’73 and ’79), but simply to stay alive while hurtling down the road on 6″ wide bias-ply tires and relying on wimpy drum brakes with no power assist to (eventually) stop.

  14. Portions of the New Jersey Turnpike have variable speed limits (which are changed according to such things as accidents, weather, and road constructions)  but they are no better obeyed than the static ones.  I have sympathy for the road workers who have semi-trailers moving at 65mph 6 feet from them.

    1. In VA and NC, that’d earn them a fine like whoa, if not a license suspension on the spot.

      Incidentally, hitting a road worker in a work zone is punishable by imprisonment in a lot of US states now.

  15. Maggie,

    As a follow-up to your “weird fact” regarding the safest speed being that of the traffic around you, I offer this. FHA data show that those most likely to be involved in a crash are the slowest 5% of drivers on the road (data divided in 5% increments). The next most likely are the fastest 5% of drivers.

    It’s perhaps because I’ve been aware of these statistics for so long that I don’t find the information you shared weird at all. Used it for years as an argument against the parents when they insisted I drive the speed limit thereby placing me in the slowest 5%. I considered that risky behavior then and still do.

    1. Well, yeah. Those signs top out at 50/55 mph, but the 85th-percentile speed (i.e., what the speed limit would be if correctly set) is more like 70.

      If the sign was 50 and is now 45, does that mean I should slow to 65, or do they really mean it? As long as speed limits are set artificially low to keep the FHP, Altamonte Springs police, and other not-as-prolific offenders ringing the cash register, I wouldn’t expect VSLs to do anything.

  16. This makes perfect sense to me too. 

    In most driving conditions, large speed differences do seem to be responsible for most multi-vehicle crashes. As long as all traffic is traveling at or below the design speed of the road, I’m all for trusting the herd. Unless smoke/fog/heavy-rain appear, that is. Then I stop trusting the herd.

    As for single-vehicle crashes, I doubt speed limits have much effect on idiocy or intoxication.

  17. Personally, I enjoy setting cruise to exactly the speed limit and watching everyone behind me get ticked off. It’s especially fun in the HOV lane if I have a friend with me.

      1.  It’s legal in Arizona. If it is illegal it isn’t enforced at least. Here it’s common to have every lane of traffic occupied by a semi going 50 in a 65. I’ll agree that going under the speed limit bothers me (unless of course roads are slick or something). So yeah, in that case I’d also say they should stick to the right.
        But if I’m going the speed limit and you’re behind me you can suck it

        1.  Try that somewhere other than Arizona and you might be sucking on a hefty ticket. Please, cut out the rolling roadblock shenanigans. It’s dangerous and immature.

        2. Looks like you’re mistaken, Teru.  The applicable law may be found here.  And once your friendly neighborhood state trooper decides he feels like enforcing it and hands you your ticket, you may suck upon that.

      2. Depends on what state you live in.  Where I live you can get ticketed for camping in the left lane for no reason.

      3. Do you mean that you stay in the left hand lane even if not overtaking someone? Is that legal?

        If there are two lanes, and the right lane is a solid mass of trucks going 55mph, you drive in the left lane and pull into the right to let faster drivers pass you.  There are no other options based on our current laws of physics.

    1. I *love* people like you! They’re the ones who I get in front of and drop down to 30 in the HOV. Just so they know how it feels.

      Yeah, OK, so I don’t, though I really want to. I will, however, call your ass in for obstructing traffic. And be perfectly within my rights to do so, speed limit or not.

      1. Some people don’t have your self-control.  Unfortunately, pulling in front of a left-lane camper (don’t know about HOVs; those apparently work different around where I live) and then hitting the brakes to teach them a lesson has caused accidents, deaths, and prison terms for the people who take it upon themselves to educate their fellow drivers.  Left lane squatters deserve a ticket, yes, but I no longer even acknowledge that deep-down urge to take those jerks to school.  It’s just too dangerous for everybody.

    2. You should plug in your GPS. You speedometer almost certainly under-reads your speed in the US (in Germany and some other places that’s illegal). So 65 on your speedo is probably under 60 in reality. 

      I just drove cross-country, at the speed limit, using cruise control and the speed reported by my GPS. I was always 5-15 mph over on my speedo and I was driving a large German car. 

      I got nervous passing cops waiting for speeders when my speedo looked ‘wrong’ but wasn’t stopped once. I conclude my GPS reads as accurately as their speed-guns and the speedo’s a deliberate exaggeration.

      FYI – I drove in the middle lane 80% of the time. I was much too slow for the left at the posted limits until I got to a hill. On the flat I was overtaken constantly.

      1. I think it’s more likely your tires need air.  I calibrate my speedometer using known mile markers and a stopwatch at 60 mph.  From my ’62 Buick to my ’07 Toyota and the fifteen cars in between, I’ve never owned a car whose speedometer’s inaccuracy was the result of anything other than mechanical failure (in a ’70 Mercury) or drivewheel tires of the wrong diameter, either because of wear, improper inflation, or just being the wrong size.  Could be I’m just a stickler for tires, but slight variations in tire size make a noticeable difference in how fast you’re actually going compared to how fast the speedo says you’re going.  I had to change speedo gears once rather than alter the tires and differential gears I wanted to use.  (It was on a Chevy 700R4 transmission, so it was easy.)

  18. When are they going to study the effect of more stringent licensing requirements on the frequency of automobile wrecks? Or the effects of harsher penalties for causing accidents?

    Because I bet the results of that would be a lot more interesting than some common sense conclusion that a wreck over 50 mph is a lot more deadly than a wreck under 10 mph.

    1. I don’t think they ever will. Us Americans have a lot of difficulty accepting the fact that bad decisions are our fault. Why do you think everything has to have a warning label anymore?

    2.  I saw a graph the other day which showed accident rates vs age.  The young drivers had high accident rates, declining until about age 25, where the rate leveled off and stayed level until about age 70, where it started to increase again.  Graduated drivers licensing helps, but other factors such as the feeling of entitlement that some people have (“I’m special; I can do whatever I want to”) are probably even bigger causes of high fatality rates. 

      There is a correlation between student GPA and accident rates; if you want your child to be a safe driver, make him/her do his homework.  Also, the correlation between speed and accident rates is deceptive; the real accident generator is aggressive driving, which for some strange reason also involves high speeds.

  19. Three most dangerous things on the highway:

    – Car weaving in and out of traffic across all lanes at high speed (or wanting to be at high speed). These often come in pairs.
    – Stick up ass going 64 MPH in the fast lane because ‘That’s the speed limit’, so the entire lane is trying to get around him/her at 75-80 MPH. Can be even worse one over since then everyone’s breaking left /and/ right.
    – Obviously totally distracted.

    Only the last isn’t a speed limit problem.

    And honestly the first two wouldn’t matter if everyone would just agree that slow traffic keeps right – hang out left as long as you’re fast or faster, but get over if someone even faster comes up behind you. Most people drive about the ‘right’ speed for the road anyhow.

    1. The speed limit applies to all lanes on the highway. The rule about slower traffic keeping right applies to vehicles that are doing significantly less than the limit. If you think it’s legal to drive faster than the posted limit because you’re in the left lane, you’re WRONG. Grow up.

      1. That’s exactly the kind of stick up ass I’m talking about. Everyone on the road is doing somewhere from 70 to 75, except for the people in the right lane (which is fine, it’s expected). It’s six lanes (each side), sloooow curves, no surprises, we’re going with the traffic flow – which is (un?)surprisingly good at finding the actual safe speed. It would, in fact, be much less safe to be going slower than the flow.

        So then you park in the left lane at 65 and are the biggest hazard in the entire commute because you think you’re morally superior for obeying the sign /and/ obstructing the passing lane.

      2. I’ve been honestly thinking about what you said, because the unexamined life isn’t worth living etc.

        These are other laws I’ve violated in my life because I haven’t GROWN UP yet:
          – I perform sodomy
          – I perform oral sex (where this is not covered by oral sex in your state)
          – I’m guilty of miscegnation (technically not, because I use contraception and have never gotten a non-white lady pregnant).
          –  I collect rain to use to water my plants (yes, this has been illegal).
          –  I  collect the excess water from my showers to water my plants (yes, this is illegal).
          – I have smoked pot to unwind with my friends, though usually it’s the totally legal and okay alcohol.
          – I have downloaded  media which is not available DRM-free for purchase.

        Forgive me, these are my sins. Hopefully some day I will be as GROWN UP as you and obey every law because it’s a law.

    2. I’m guessing you’re one of those fine upstanding citizens who, when I pass the vehicle in front of me that’s going 5-10 mph under on the right, decides to speed up and try to park your car in my back seat despite following me at speed limit for 30 miles, because hey, driving speed limit in the left lane is WRONG.

  20. Perhaps this is covered in the article, but ‘safety’ shouldn’t be the only issue considered here. I remember reading somewhere (where is the citation?) that slower speed limits can sometimes increase highway throughput, because they increase the efficiency/decrease the disruption of people merging on and off the road.

    Edit: Here’s a Slate article on what I said about slower being more efficient. I hadn’t remembered it correctly. It had nothing to do with speed limits per se, but “speed harmonization” — making everyone go the same speed by slowing down the faster drivers.

    1. Also, in Washington anyway, you can get ticketed for impeding traffic if you’re doing 65 in a 50 mph zone and traffic starts stacking up behind you.  The WSP usually saves that ticket for the real rectal orfices.

    1. The first 5 miles on surface streets are the most dangerous because of that acclimatization you mention.

  21. Let’s keep in mind that this is only useful for freeways.  Other streets, which are shared with pedestrians and cyclists, are undeniably safer for all when speed limits are set (and enforced) low.

  22. If half of people exceed the speed limit on a regular basis (very conservative estimate), and 1/3 of accidents involved excessive speed, then isn’t speeding safer? 

  23. FWIW, I *highly* recommend Tom Vanderbilt’s Traffic: Why We Drive the Way We Do.  I’ve been working my way through it in the last few weeks, and it’s a great examination of US roads and how we use them.  He’s be an excellent BB guest, I’m thinking.

  24. What I find fascinating in this discussion is what’s missing: fuel economy. Air resistance is proportional to the cube of speed, so fuel economy should decline as the car goes faster.  Increased fuel economy was the justification for the old 55 mph speed limit.  According to Wikipedia, there may not have been much actual fuel savings in the 65 –> 55 mph change,  but actual data from a variety of vehicles shows pretty drastic decreases in mpg in the range between 65 and 85 mph.
    (Scroll down to see the graph.)

    1. There was that entertaining segment on Top Gear wherein someone drove a Toyota Prius as fast as it could go around a track while Jeremy Clarkson kept pace in (I believe) a BMW M3.  He said it was one of the most boring races he’d ever done.  Anyway, turned out the BMW got significantly better gas mileage at that speed than the Prius did, because the Prius is not designed for optimum fuel economy with one’s foot to the floor.

      1. Clarkson HATES the Prius, so I’m not surprised that he would set up a rigged test. At normal highway speeds (even up to 65 or 70 MPH) on level ground, a Prius will generally switch to electric mode and boost its average MPG significantly. Once Google comes out with the autopilot upgrade for the Prius, I’d expect mileage to improve some more as our robot friends should be much better at drafting than humans.

    2.  I believe that’s V^2, not V^3.  Parasitic drag (wing roots for example) exhibits the cube function.

  25. There is a similar debate here in Michigan. From what I gathered, driving in the 90th percentile for speed is the safest, and driving much slower than the natural pace of traffic is much more dangerous than speeding. The Michigan State Police raise the speed limits for freeways going through major cities (from 55mph to 70mph)  on a case by case basis once enough research is done. The full Mlive article is here .

    Also think of the economic impact of driving faster. Less time in the car means more time for making or spending money. Goods can be shipped faster, thus increasing the productivity and efficiency in a firm’s logistic operations (i.e. if trucks can go 5 mph faster we will save X amount of time, and can schedule X additional routes per year).

  26. we just need fully self driving cars, they’ll be able to handle much higher speeds than humans, much more safely

    1. I was wondering about that.  Once the day comes when we’re all zipped up in our self-driving Googlemobiles, which will merge automatically onto the speeding freeway matrix and keep optimum following distances, I’m sure travel will be both safer and quicker than it is now (eventually).  But will it actually be faster?

      In other words, if all cars automatically maintain a mutually agreed-upon speed and following distance, and communicate their intended lane changes and exits, etc., to each other, will they tend to travel significantly faster than average traffic does now?  Or will the cars travel more-or-less the same speed they do now, and simply get you there quicker by improving efficiency and economy of movement, and thus optimizing the volume of traffic handled?

      1. Are we talking about shaving 10, 15, 20 minutes off a commute to work?  An hour or two off an all day drive to Grandma’s house? ‘ Significantly faster’ would be subjective at first, and then eventually irrelevant.

        I’m going to give that question a tenative ‘yes’, if we take human behavior out from behind the wheel, where driving now often appears to be No. 3 or 4, on the driver’s list of multi-tasked priorities, then the driver becomes a passenger only, while car has but one task.

          1. Agreed, the commute would perhaps be more satisfying for the former driver. 

            Donald’s question is about whether the drive would be ‘significantly’ faster, a point of satisfaction in itself.  I think the drive will be faster by taking out the me-centered, inattentive, stop-start of human behavior behind the wheel, when we leave the driving to the car. 

          2. I should have been more verbose, but I’ve been working to unset that flag of late.

            I feel that it would be effectively faster because while a two hour trip might still take two hours, it wouldn’t subtract nearly as much time from my day.

          3. My own imprecision of language is to blame.  Though up until recently the thought of handing over my control of my vehicle to automation filled me with crawling horror, I think I’ve largely made my peace with it.  (It’s this same fallacious feeling that we’re safer when we don’t give up control which leads to thirty thousand fatal automobile accidents in the U.S. per year compared to one or two hundred plane crashes worldwide.)

            I’ve no doubt that once the kinks are worked out (and the viscera hosed off the blacktop), drivers will be able to enjoy a restful commute similar in safety and reliability to mass transit, albeit with greater comfort and privacy.  And I also have no doubt that commutes will be shorter in duration due to more efficient handling of traffic.

            But my question was about physical velocity.  An automated traffic-handling system should be able to handle merging traffic like interlocking teeth in two gears, and since all vehicles should be able to react to each other’s presence and motions with far greater speed and precision than human senses could handle, the vehicles could travel much closer together at higher speeds.

            So I just wonder if we’ll end up with streams of bumper-to-bumper traffic hurtling along at 120 mph (or more, on longer stretches of uninterrupted highway), or if we’ll see average speeds much closer to, say, 60 mph on a busy urban freeway, albeit a steady 60 that feels like driving downtown at 2:30 am on a Monday morning.

            At a certain point, a given freeway’s capacity will be overmatched by the traffic, no matter how automated, but before that point we can hope for flying cars, sterner population control, or zombie apocalypse.

            Or Rapture, I guess.

          4. Some people, myself included, get motion sickness much too easily to be productive as a passenger in a car, bus or train. I suppose eating and other tasks that can be done while looking out the window or sleeping might be possible for some such people, but I don’t see time in transit as universally reusable.

      2.  Efficiency is what makes the trip shorter.
        Even if the automatic cars travel at the same MPH as human-driven cars, they should be faster in terms of elapsed time over distance. Ideally they should not ever experience traffic jams. ‘Traffic waves’ would certainly become a thing of the past. Traffic lights would be obsolete, automatic cars would be able to negotiate intersections car-by-car in real time. All these things should shorten trips considerably, the last reducing some trip times by about a third in urban conditions.

      3.  Even if trips take longer in an automatic car, it is effectively shorter because you can do other activities while your attention isn’t taken up with driving.

  27. Since everyone’s assuming increasing safety is a primary goal, I feel compelled to point out that if we were all dead and buried we could no longer be hurt, and would be eternally safe from all forms of suffering and harm.

    In reality nobody wants perfect safety, though, since you’d have to be dead to achieve it.  So really it’s a matter of determining what level of danger you are willing to tolerate.

    I’m toying with the idea that as people become more terrorized, perhaps they get less willing to live dangerously, and more willing to use state-sponsored violence as a means of forcing others to submit to restrictions on free expression in the name of ensuring their own safety.

    Hmmm, my prose is still too prolix.

    St. Louis!

    By profession, I am a civil engineer who has been designing urban interchanges for almost 10 years.  “Road Conditions” is a simple description of what engineers like myself spend years in school learning the physics behind what people spend entire careers creating.  Yes, weather.  Yes, other drivers.  Yes, traffic density and congestion.  But “Road Conditions” also includes design and construction, which is based on available historical statistics and data (85th percentile tire side-friction factor for instance.) that is ever-changing, and economics as well.  The results usually end up with design policies that have large factors of safety (which is why buzzing around a corner 15mph above the advisory speed in dry weather isn’t usually an issue these days).  The factor of safety for a road in 1977 is different than the factor of safety for the same road today because of the change in the average user.

    So, yeah, a one-size fits all speed limit doesn’t work from a weather and traffic standpoint, but it also doesn’t hold true for the infrastructure itself over time.

  29. Some things to keep in mind about that 85 mph zone in (ok, near) Austin:

    1. A large percentage of Austin’s populace is on allergy medication a good part of the year.
    2. There is a persistent cloud of cannabis smoke hovering over the central part of the city.

    Given these two factors, it is extremely common to find drivers poking along at 50 mph in the left lane of the freeway.  Thus, with the introduction of this 85 mph zone, it’s  as though they’ve given snorkeling equipment to someone in the Sahara.

  30. If idiots want to get out there and kill themselves on the roads that I don’t use, fine.  Less traffic on the roads I use, and we certainly don’t have a shortage of speed freaks.   Natural selection in action.

  31. Referencing the very beginning of this thread:

           Data is …. a character in Star Trek TNG

    I’m just saying …

  32. I don’t want to be on that road with the people I know will be there, thinking its okay to drive 85 mph while talking on the phone or texting, which will allow the first irregularity in the surface or unforseen move by another driver to turn their Suburban into a 2 ton unguided missile.  SUVs don’t handle well at 65, much less 85, and no one is getting good mileage at that speed…

  33. Maybe Google’s self-driving cars will fix this.  I’ll bet they can be programmed for road conditions.

    1. More importantly, if the car automatically obeys the speed limit, raising revenue through traffic enforcement is no longer possible.

    2. For some reason, this reminded me that in Oman, the cars are required to have an alarm (like the door chime) that sounds whenever the car exceeds 120 kph.  My boss drove a car from Dubai to Muscat – gunned it – and said the alarm did that the entire ride.

  34. Large portions of Interstates 10 and 20 in west Texas are already 85MPH (slightly west of Midland/Odessa to just east of El Paso) and have been for years. It is very nice if you have a car built for the autobahn.

    I recall reading that the majority of accidents are caused by the lowest and fastest 20% of the traffic, with near universal agreement that the biggest single contributor to accidents is speed differential (which is why different speed limits for trucks and cars is a Bad Idea).

    1. Indeed.  That stretch is almost exclusively two lanes each direction; I’ve made that drive more than once.  It’s nice to set the cruise control to 90 and eat up the miles.  Unfortunately, that entire stretch is plagued with locals going 50mph and tractor-trailer rigs straining to get up to speed for miles (it’s mostly uphill when you’re westbound, even though it doesn’t look it) and often passing each other in the attempt.  Few things are as fun as knocking your speed down from 90 while you wait for one semi traveling 45mph in the left lane to pass another semi doing 43mph in the right lane.

  35. Over the last 50 years, the fatality rate on State highways in Texas (130 is a STATE highway) have ranged between 5 to 7 per 100 million vehicle miles (txdot). Conservatively, this means 280 deaths per 100 million vehicles using a 40 mile stretch.    

    (Maybe this is mixing apples and oranges, but I’m trying to be conservative and there are more fatalities on interstates.)  Let’s assume that a 15 mph increase (like the 15mph increase effectuated by the 1995 repeal on interstates) will increase fatalities by 9 percent on the 40 mile stretch (from the article)  That’s 25.2 more deaths per 100 million vehicles using the 40 mile stretch as a result of the speed increase, IF Hwy 130 was the most dangerous stretch in Texas (it isn’t) and if it was also an Interstate Hwy (it isn’t).  

    Wikipedia tells me the average U.S. lifespan is 78.2 years.  Each vehicle saves about .1 hours from a speed limit increase of 70mph to 85 mph over the road’s 40 mile stretch.  So the speed increase, by contrast, would SAVE about 15 lives in lifetime hours per 100 million vehicles using the 40-mile toll road.  

    And make no mistake, boredom is lethal.  

    Much ado about nothing, I think.  

  36. A few things:
    First off, why come, despite clicking the “remember me” button EVERY TIME I log in, it never does?

    They tried the variable speed limit thing around here, at about the 7 o’clock position of the DC beltway.  It didn’t work.  Nobody paid any attention to it.  Cops pulled a bunch of people over but in the end they pulled the very expensive signs down and replaced them with normal ones.

    I’m a US citizen. Born and raised.  Recently I was fortunate enough to travel to Europe. 
    I was amazed at how different the driving experience was over there. 
    -First, everyone seemed to be better drivers.  People still had lapses of judgement, hell we got run off the road by someone passing a huge farm truck, but by and large everyone had their shit together.
    -Speed limits are set much more reasonably.  It’s 50kph in villages and towns, sometimes 30 in very  crowded areas. But it goes up to 80-100 as soon as you leave the village. 
    Imagine the most fun twisty narrow country road you can think of… now imagine that the speed limit is 50-65mph.  I KNOW, RIGHT? 
    On the highway it’s 130kph, or about 85mph. 
    Honestly, I didn’t want to go any faster, and I’m a chronic speeder here in the US. 
    I don’t know what the crash data says for Austria, but I sure didn’t see any accidents, and very few damaged cars in the 11+ days I spent there.

    Next subject, the data.  Ok, so 20% of crashes involve excessive speed?  That means 80% don’t.  What are the causes there?  Texting, failure to follow signs, DUI, etc?   How about we spend 80% of our time and money on those problems.

    Personally, I think our driver’s ed system is terrible.  The idea that one can get a driver’s license in a Geo Metro and then be qualified to drive a huge SUV is patently ridiculous.  There should be tiers for licenses depending on what kind of car you own.  If you want to own a large truck or a fast car, you have to prove you can handle it.  This would bolster the car rental business and lead to companies renting cars that I’d maybe want to drive on occasion. 

  37. I believe it was in Vanderbilt’s previously mentioned book Traffic that I read how speed can become a “factor” in accident stats:  someone runs a stop sign going 50 in a 40, and T-bones another car.  Since the car was speeding, speeding goes into an accident report and eventually into the statistics, even though the true cause of the accident was not the speed of the offending car.  Arrrrrrgh.

    In the world of trauma nursing, speed surely does have something to do with injuries present.  We speak of “mechanism of injury,” and part of that is noting the approximate speeds of the vehicles involved.  This gives the  seasoned practitioner  a grasp of injury potential, and raises our index of suspicion if the involved speeds are high.  However, things like being hit from the side, not wearing your seatbelt, and rolling your car over, are also very highly related to injuries suffered.  We also add in “prolonged extrication time,” as this can tremendously correlate to suffered injuries.  There are many checkboxes on our forms, and they really matter. 

    One neat example is auto-pedestrian collisions.  As the speed of the vehicle raises above 20mph, death of the pedestrian becomes increasingly likely.

    All this crazy data actually gets tracked in level1 trauma centers, and fed into trauma research and best practice guidelines for patient care. 

    Denver, CO
    the Fiat RN 

  38. The problem with an 85 mph speed limit is that most people will go 95.  People always go about 10 miles an hour over the posted limit. If I drive 55 in areas that are posted at 55, everyone passes me like I’m standing still.

    1.  We should note as well that if the maximum probably-safe speed for the average driver and vehicle is N, the police will post N-10, since they have to leave a margin for the below-average drivers and vehicles.  Most drivers will then assume that the speed limit has been adjusted downward, and adjust it upward for themselves, since they will regard themselves as above-average.

      However, I enjoy driving the posted speed limit, however risky that may be, because it annoys people so much. 

  39. What is the allowed tolerance for speedos in the USA?

    In the UK its -10%/+0%, so two people can be doing 70mph on the speedo, but one is really doing 63mph.  I do wonder why we cannot fix something this simple.

  40. And then there’s the fuel economy argument … I read yesterday that each 5 mph over 60 mph reduces fuel economy by 7-8%.

  41. Spent some time in Germany recently, and the autobahns there have variable speed limits. There’s also a far greater disparity in traffic speeds than on your typical American freeway, so you have to be alert at all times, lest you either a) run into a truck doing 50 kph, or b) get run over by an Audi doing 180. This required awareness -and good brakes- might account for their accident rates not being astronomical.

    Off the autobahn,  driving the posted speed limits will guarantee the accumulation of impatient locals behind you. 

    1. Well, add this to the fact that the German system concerning driving (this is mostly true for all of Europe in some extent) is different as well.

      For example, in the US you could as well get your license in a cereal box and be done with it.. in Germany, you actually take theoretical lessons (14 at the time I got mine) and about 30 driving lessons including high speed driving, emergency braking, handling of emergency situations etc..) which costs you about $2.000 for a simple car license. Licenses for bikes are even categorized by CC, so you need to have a much more extensive license to be allowed to drive bigger bikes.

      Also, every! car in Germany is forcibly put into a stringent checkup by mechanics (called TÜV in Germany) every 2 years checking the safety, condition of tires, functionality of all parts safety-related (lights, etc).. and if they don’t deem your car fit for the road anymore because your tires are out or your brakes don’t work that well anymore..they just prohibit your car from hitting the road AT ALL until it is fixed.

      I personally drive a Ford Mondeo (Fusion in the US) with 2000CC/145HP Engine and my regular highway speed is about 120mph – still I felt more secure driving in Germany to when I was doing 65 in the US, because there the drivers just didn’t look out so much for what everyone else was doing than in Germany – as the OP said, never beats the adrenaline if you do 80mph on the passing lane and a Porche from behind is coming flying in at 180mph..

  42.  Agreed! I remember a few years ago a young driver killed himself by running into the edge of a concrete barrier and his mother started a campaign to improve the safety of these, for example by placing barrels full of sand in front of them. This would slow the vehicle sufficiently that it would no longer impact the barrier with fatal force.

    It occurred to me at the time that it would be much simpler if people would just not run into those barriers edge-on! In fact, why not just remove the barriers entirely? They are entirely unnecessary if people merely pay attention and stay on the road.

    Unfortunately human beings are simply not very good at paying attention for sustained periods of time. Automating driving will solve that problem, along with many others.

  43. I drove 20,000 miles per year in Montana when our speed limit was, “Careful and Prudent” (no numerical speed limit.) The biggest danger was when people were driving vastly different speeds. I could be driving 80 mph, pull into the left lane to pass and then have someone come up behind me doing 100 mph. 

    Interestingly, Montanan’s at that time averaged driving only 78 mph on interstate highways. 

  44. The problem with driving is this: we have positioned ourselves in the exact same place in our cars that our eyes occupy in our bodies. As long as we occupy that spot we will identify with our cars. So being told to slow down is as offensive as being told to walk differently. And everybody assumes they’re paying 100% attention when that’s hardly the case. 

    We all need to take a break from the hot seat before we can have a cogent conversation about cars and other modes of transportation. 

  45. Reminder:  The national 55MPH limit was put in place when we were worrying about being blackmailed by OPEC, in an effort to conserve fuel.

    These days, people are barely giving lip service to fuel efficiency, even during a major recession when the money saved could make a significant difference.

    Yeah, I know, there’s almost nothing in Texas worth slowing down to look at or stopping to visit. But I’m still not convinced that this would make sense if we hadn’t bred several generations attuned to instant gratification. And I’m not exempting my own.

    1. If I have to save fuel, I’d certainly rather drive a small car to my destination in 8 hours than spend 14 hours in a Hummer.

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