From Practical Engineering:
Traffic management in dense urban areas is an extremely complex problem with a host of conflicting goals and challenges. One of the most fundamental of those challenges happens at an intersection, where multiple streams of traffic – including vehicles, bikes and pedestrians – need to safely, and with any luck, efficiently, cross each others' paths. However we accommodate it now or in future, traffic will continue to be one of the biggest challenges in our urban areas and traffic signals will continue to be one of its solutions.
