For the first century of the automobile's use, passengers were always people or pets. However, in the past decades, automobiles have begun to carry a new "passenger": a voice-based computer agent used to give directions, warn of problems (e.g., "your oil is low"), control entertainment (e.g., "you are now listening to KQED"), and make suggestions (e.g., "the closest Starbucks is 2.3 miles away"). As a social scientist who studies human-technology interaction, I've guided my design of and research on these "virtual passengers" by studying real passengers. By leveraging those attributes that make passengers likeable and non-distracting, one can then make GPS systems, voice-activated controls, and other voices in the car more desirable and effective. For example, we've found that people adjust their way of speaking to match the situation in the car: when the driving is dangerous passengers unconsciously shorten and simplify their sentences. There are now GPS systems that do the same. Similarly, when BMW found that German drivers wouldn't take directions from a female voice and had to have a product recall, they found a voice that better matched their brand: a male "co-pilot."
One of the most important issues to address in car interfaces is how to deal with upset drivers, as negative feelings are among the primary causes of accidents on the highways. Unfortunately, there is little known about effective strategies that passengers can use when dealing with an upset driver. In particular, should a passenger — real or virtual — in a car with an upset driver sound happy and upbeat or depressed and morose?