Oh, traffic lights. The bane of my career. (Image Sources: Flickr: Vit 'tasuki' Brunner, grendelkhan)
The traffic light's purpose is to regulate the flow of traffic between two intersections. However, their design does not always match up with the actual traffic flow. A major road admittedly needs more time than a minor cross street to let traffic through. But often, traffic lights run on an arbitrary timer that is designed to guess how much time traffic needs to clear out. For a car driver, being stuck behind a light is a hindrance. For those who ride public transit, though, the hindrance can be a nightmare, especially if they need to transfer.
Consider this fiendish situation in traffic lights: In the Bay Area suburb of Walnut Creek, California, there is a traffic light at an off-ramp exit of Interstate 680 North that leads directly into the Walnut Creek BART station, a commuter subway to San Francisco. The road intersects with Ygnacio Valley Boulevard, a major road in the city. When the signal is red for those coming from the exit, it takes up to three minutes for the traffic light to change so vehicles can cross the street. To some people, that is an annoyance. But passengers who use the public transit bus to transfer to a BART train or another bus, this is the worst possible scenario. More often than not, a rider will miss a train or bus because they had to sit at a traffic light for more than a critical two or three minutes, all the while little-to-no traffic is passing through the very road that has the green light. Given how infrequent both BART trains (up to 15 minutes) or public transit buses (up to 30 minutes) run, that can be the difference between being on-time at a job and being fired. Sometimes, that also includes being given a green light time of less than 20 seconds.
Other examples of terrible traffic lights can be made in suburbs and cities across the country, and not just in frustratingly long waits between traffic lights, but also being forced to stop every ten seconds when there is a large number of stops and traffic lights that are ignorant of buses. Such is the case with San Francisco's Muni system, whose high stop density in a dense city, and arbitrary stop lights means that buses run an average of just over 8 miles per hour, the slowest in the nation.
Traffic lights do not have to be like this, though. Emergency vehicles such as ambulances and fire trucks, as well many street level trains, are given the ability to pre-empt, or change, the normal operation of a traffic light so that they are given priority to clear the intersection. With trains, the process is called transit signal priority. Such a process should not be hard or expensive to incorporate into a bus system, since preemption is already in place for emergency vehicles. By incorporating something that basic, problems like the ones mentioned above would not happen, at least as often. Traffic lights would not be the bane of bus riders everywhere if simple investments were made to improve them for buses.