Ramp metering magic

Here is a recent article giving some history on the invention of ramp meters, used on highways to mitigate congestion. I discuss this subject in Numbers Rule Your World (link).

There is an interesting stochastic phenomenon underlying highway congestion. Ramp meters help by regulating the inflow of vehicles onto the highway, and prolonging the period of time by which the highway runs at full capacity. The key insight is that when the highway breaches its capacity, it does not run at maximum throughput - it runs at less-than-maximum throughput.

In the book, I also discuss the fascinating large-scale experiment in Minnesota some years ago that generated nice statistics to support the theory of ramp metering.