Google’s Arterial Traffic Data Makes Us More Efficient, Or Does It?
To make planning your next trip across the city a little smoother, Google Maps has implemented live traffic information for arterial roads. The service uses GPS enabled smart phones with the Google Maps application to crowdsource its data. With many devices telling HQ how fast they are traveling, a fairly accurate picture of where congestion is or isn’t can be presented. The ability to view traffic history also makes it easier to predict future conditions.
Tools like this make life easier, but there are concerns that if large numbers of drivers all try to optimize their route at once, even more traffic can ensue. The mathematical formula of Braess’s Paradox has shown that adding capacity to a network in which all the moving entities rationally seek the most efficient route can sometimes reduce the network’s overall efficiency.
The Christian Science Monitor reports:
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.
Note that this still happens even if – indeed, especially if – all the drivers have perfect information about what all the other drivers are doing, such as with a GPS that gives real-time traffic updates.