Clustered in the Morning
My morning commute, from home to the local train station, largely consists of about 4 miles of driving north along a main road. Unfortunately for me, this main road is used by thousands of other commuters, either heading to the train station, a local employer, or the highway.
On an ideal day, with little or no traffic, I can make it to the train station in 15 minutes, so I would give myself about a 5 minute buffer for parking and walking to the platform. Thus, I’d leave about 20 minutes before the train is due. On a typical weekday morning, I give myself about 30 minutes.
However my actual commute can vary dramatically, with a swing of over 10 minutes, based on a couple of factors. The first is the light where the north-south main road meets an east-west main road. The intersection just does not have the capacity to handle rush hour, and sometimes it can take several cycles of the light to make it though. The second factor is that the dominate north-bound traffic pattern is a cluster of about 30-60 cars. If I get in front of such a cluster when I turn on to the main road, I can make it to the light with fewer cars in front of me. This results in sitting through fewer cycles of the light. If I get stuck behind a cluster, it will literally add minutes of waiting at the light.
A few seconds turns into a few minutes. And the alternate routes are no better.
One of the reasons the intersection is so bad is that it was designed without foresight. Sure, back when the road was put in, far fewer people drove on it. But still some basic common-sense features should have been added. For example, when waiting at the light in a northbound lane, there is no right-hand turn lane. This prevents a number of cars from being able to make a right on red, and these cars add to the congestion for everyone who is going straight. Also, the left-hand turn lane is just a single lane and very shallow. Cars that could take advantage of it are usually stuck behind the cars that are going straight.
In other words, it’s an inefficient mess that a few minor changes could dramatically improve. Make your analogy to software design now.
A way of eliminating these traffic choke points is to widen the road through the intersection, adding one or more deep turn lanes in either direction, and an additional straight lane if possible. This would get many more cars through each cycle of the light, reducing backups and delays, and mitigating the impact of clusters.