Thursday, July 16, 2009

Few Roads = Faster Traffic?

Counter-intuitive, huh? Reduce choice, improve efficiency?

Apparently, traffic jams can be eased by closing roads, or making them one-way etc.

Check out this blog. It refers to a study, in which:
The authors give a simple example of how this could play out: Imagine two routes to a destination, a short but narrow bridge and a longer but wider highway. Let’s also imagine that the combined travel times of all the drivers is shortest if half take the bridge and half take the highway. But because each driver is selfishly trying to seek the shortest route for himself, this doesn’t happen. At first, everyone will go for the bridge because it’s shorter. But then, as the bridge becomes backed up, more drivers start taking the highway, until the congestion on the bridge starts to clear up. At that point more drivers go back to the bridge, which then becomes backed up again. Eventually, the traffic flow settles into what’s called the Nash equilibrium (named for the beautifully minded mathematician), in which each route takes the same amount of time. But in this equilibrium the travel time is actually longer than the average time it would take if half of the drivers took each route.

A related topic can be found here. Quoting from the article:
Tom Vanderbilt, in his authoritative book Traffic, describes a simple experiment performed by the Washington Department of Transportation that involved a liter of rice, a plastic funnel, and a glass beaker. When the rice was poured into the beaker all at once, it took 40 seconds for the funnel to empty; the density of jostling grains impeded the flow. However, when the grains were poured in a gradual stream, it took only 27 seconds for the rice to pass through. What seemed slower actually turned out to be 30 percent faster. This helps explain why traffic engineers are so eager to install red lights on highway onramps: By slowing traffic before it enters the concrete funnel, they hope to prevent the road from exceeding its critical density.


Sunny Red said...
This comment has been removed by the author.
Sunny Red said...

Nice one Sachin!

Intelligent transportation systems can easily take care of the first problem. I agree that one way roads increase traffic flow. Downtown system is a good example.

It is always difficult and at the same time important to balance efficient flow and safely; that’s why the signals, medians and all that crap.

July 18, 2009 12:56 PM

Sachin Shanbhag said...

yeah, these traffic flow problems are amazing for somebody who does modeling and simulations