I used to think that traffic engineers weren't too bright, based on some of the wacky road configurations I've seen, especially around Boston. Now I'm not so sure. I was thinking about how silly it is for a road to widen near traffic lights - after all, doesn't that just create a merge problem on the far side of the light? However, when I thought about it a different way, I began to see the logic.
Basically, if you think about a traffic light as a valve in a pipe, and the traffic itself as fluid flowing in that pipe, then to maintain a near-constant flux of fluid, it makes sense to widen the pipe near the valve. The reason for this is that traffic moves slower near the light, simply because the light interrupts the stream periodically. To keep cars flowing at a constant rate toward the light, they must be allowed to pool before the light. Then when the light changes, the road must remain wide for a while to accommodate the slow moving blob of cars. As the cars accelerate, gaps in the blob appear, which affords drivers opportunities to merge smoothly.
There are still some traffic patterns I dislike. For instance, why do so many on and off ramps reach their maximum curvature about halfway through the curve, instead of having constant curvature or biasing the maximum curvature towards the end that has the slower traffic? If the goal is to encourage drivers to slow down on ramps, this seems to be a fairly dangerous way to achieve it.
I also find clover leaf patterns at highway intersections to be dangerous. The outflow of some ramps is perilously close to the inflow of other ramps. When two streams of traffic cross like that, there is what I would consider the analog of turbulence in the flows, making for hazardous conditions. I don't know what pattern would be better - perhaps all on ramps should enter from the right, and all off ramps should exit to the left. This would work well if the on and off ramps were sufficiently separated.
Well, I guess I have a negative attitude while driving - I'll blame years of "Drive Defensively" indoctrination. I suppose I'll leave traffic design to the professionals - Lord knows I can barely walk in a straight line, never mind deciding how wide a road should be a given distance from a traffic light.
You can respond to my ranting here.
All rants lead to Rome.