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I was thinking the exact same thing. If you have traffic flowing at 40 mph in 2 lanes with 2 car lengths gaps (3 total car lengths per vehicle), and you constrict it down to one lane, you have to either zipper together with only 0.5 car length gaps (1.5 total car lengths per vehicle) and remain that tightly spaced for the whole duration of the constriction, or speed up to 80 mph for the duration of the constriction and keep the 2 car length spaces, or some intermediate combination of speeding up and reducing spacing.

Anything else results in a higher rate of vehicles entering the constriction than leaving it, and will necessarily cause continually increasing traffic density.

The techniques in this article might help in moderate traffic jams if applied only during the approach to the congestion, not once inside it, but the real solution to a serious traffic jam is for the people to exit the congested area as quickly as possible.

I've witnessed traffic jams forming, and it seems to happen when traffic reaches a certain density. If there's a lane closed for construction, or simply an entrance ramp merging into the expressway, it's often enough to trigger it.

If people watched their rear view mirrors and tried to maintain an equal gap ahead and behind them, it might help because then upstream pressure CAN force the traffic downstream. As traffic gets heavy, you decrease the distance to the car ahead of you, and that car then decreases the distance to the car ahead, compressing the traffic fluid and increasing pressure. If everyone responded to "tailgaters" by speeding up as much as they could (within reasonable safety limits), then eventually this forward moving pressure wave would reach the front of the congested area, and the cars at the front with no constrictions would speed up to relieve pressure.

The difficulty with this is that everyone needs to be willing to drive fast in tight formation, and alert enough not to cause an accident while doing so. Also, people toward the front need to be willing to risk speeding tickets if necessary to relieve the pressure behind them.

I'm not a fluid dynamicist, but it seems like the normal "one-directional" pressure response of traffic would make it behave a bit differently from ordinary fluids, and encouraging drivers to engage in space-balancing the gaps ahead and behind them would allow a bi-directional pressure response and make it behave more like an ordinary fluid.

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