Thursday, January 10, 2008

Traffic jam mystery?

Economist's View pointed to this from EurekAlert:
Mathematicians ... have solved the mystery of traffic jams by developing a model to show how major delays occur on our roads, with no apparent cause. Many traffic jams leave drivers baffled as they finally reach the end of a tail-back to find no visible cause for their delay. Now, a team of mathematicians from the Universities of Exeter, Bristol and Budapest, have found the answer and published their findings...
Their model revealed that slowing down below a critical speed when reacting to such an event, a driver would force the car behind to slow down further and the next car back to reduce its speed further still. The result of this is that several miles back, cars would finally grind to a halt, with drivers oblivious to the reason for their delay. ... The jam moves backwards through the traffic creating a so-called ‘backward travelling wave’, which drivers may encounter many miles upstream, several minutes after it was triggered....
The research team now plans to develop a model for cars equipped with new electronic devices, which could cut down on over-braking as a result of slow reactions.

My feeling was that this was no great mystery and has been shown before. This point of view seems to be validated by some comments on EV. My attention was on the proposal for a remedy: Does the proposal pass some cost benefit analysis?
1. How frequently do these random slow downs occur? On any given stretch of 1000 miles how often does this happen?
2. Like others I tend to think that the problem occurs mainly on some exits and entrance ramps and feel that money would be better spent making merge on exit or entrance a little safer and easier.
3. I also think that the traffic simulation models which are used for highway construction have failed in the following sense: Highway construction that was based on the time when the speed limit was 55 mph is no longer optimal now that speeds are 65 mph. It's a lot harder to merge into and out of short merge lanes in when cars are traveling a lot faster.

No comments: