Traffic jams with plenty of road space.

Traffic jams are sometimes caused by too many people trying to drive on road that's too small. However some traffic jams happen even when their is plenty of road space. This post explores why this happens with today's cars and how these traffic jams will be fixed with fast self driving cars.

To demonstrate the concepts  I'll use a simple web based traffic model. You can play with this model to see what else causes traffic jams. 

First, the simulation shows traffic on a circular road. At first the cars drive without issue, but after some time you can see speed perturbations (acceleration & deceleration) form because each driver can slow down faster then they can speed up. Eventually a jam forms where cars are nearly stopped which causes the cars behind them to stop. 

How can we fix this? There is plenty of room on the road.

You can completely eliminate these types of traffic jams simply by increasing the max acceleration rate of the vehicles to match their comfortable deceleration rate. This essentially helps pull cars out of traffic jams so that they don't slow down the cars behind them.

This is really hard in practice on public highways because no sane regulator will advocate for people to drive faster to reduce traffic jams, even if on paper it will be safer. Also, some vehicles like trucks simply can't accelerate fast enough to avoid causing traffic jams. There's no hope to solve this problem on public roads where there is a wide range of vehicle performance.

However, on roads where the specifications of all cars can be defined (like the simulation) these traffic trams could be engineered away by only allowing cars to accelerate as quickly as they decelerate. Who knows how much energy this would save, but its a lot. This is one of many reason why I'm advocating to create a purely self driving right of way on tracks BART tracks.