March 4, 2010

Thoughts on optimizing traffic flow at lights

We've all been there. You're at a red light, the light changes to green, and, what feels like eons, pass before the car in front actually starts moving. This effect gets worse the further back in the queue you are. You can see the light is green, but why is nobody moving? You're gripping your steering wheel harder, circulation to your fingers is being cut off and you want to gnaw on your air freshener out of sheer frustration that you're not going to make this set of green lights, from a distance you blankly stare at the 6 cars that made it through the intersection*.

What if the problem isn't people's attention span, but reaction time. Here's what I assume is the train of thought cascading from car to car:

  • The light changes from red to green
  • Car #1 in queue realizes "Awe, snap, it's green" and starts moving
  • Car #2 has already realized it's green, but is waiting for car #1 to move
  • Car #3 knows it's green and is worried why Car #2 hasn't started moving yet and is patiently waiting for Car #2's break lights to dim so he can move
  • Car #4 (probably me) is going through aforementioned effect of sheer insanity of slow moving traffic.
I know I check the crossing lanes' lights for changes when I'm first in line at a light. Either by looking at the pedestrian hand or catching a glimpse of red / yellow hue from the actual light. This way I can ensure I'm rolling by the time I get the green. There are three problems with this, first is I'm taking my eyes off what's going on right in front of me. Second is I'm confident not many check the crossing lanes' lights. Three, the car behind me and behind it probably can't see that hue of the crossing lane's light and while I might be able to move that split second earlier anticipating the change of the light, the car behind me will essentially be the new Car #1 in the above scenario - shifting the effectiveness of my over-attentiveness by only one car.

I would propose a slight change in the way our traffic lights work. Add a red/yellow phase before going to green. Everyone knows lights switch from green to yellow to red when bringing your lane(s) to a stop and switch from red to green to start traffic. This red/yellow phase would be inserted to get traffic moving. While sitting at an intersection the light would be red. It would then switch to having both red and yellow on, before switching completely to green.

Benefits of this system (which is in place in many countries, especially those with mostly manual shift cars) is that everyone in all lanes, and many cars back in the queue, can see that the intersection is about to switch to green and can prepare to move. Cars can start inching forward during this phase and the entire intersection can get moving faster.

One might argue that adding the extra red/yellow phase may slow the intersection down - but considering most intersections in Canada are red in all directions for a full second before switching one direction to green this red/yellow phase is inserted in the second the crossing lane has been switched to red. Others might say there's no need for the extra yellow phase, as manual transmissions are going the way of the dodo in North America. I can only rebuttal with reaction time. It still takes enough time to realize the light has changed to green, and ones foot to move from brake to accelerator.

Perhaps, as always, I'm biased the EU has had four phase lights since I can remember and North American lights still catch me off guard. I always peak at the crossing lanes' lights to ensure I'm rolling by the time my light goes green.

Anyone want to crunch some numbers to figure out how much time / gas could be saved in a life time cutting idle time at traffic lights?

* - I exaggerate, of course, but it sure doesn't feel like many cars get through on green (turning arrows).

Update: Apparently I'm not alone on this. Noel Schutt has a nice post on this, too.

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