When everyone take the fastest route

This is a clever paper. I didn’t know this. I mean, it seems obvious once you hear it, but I didn’t know it.

Reading this reminded me of something I heard someone say, maybe Liv Boeree or someone like that, on a podcast. She said something to the effect that individual rationality can lead to collective irrationality. Individuals optimizing for things that are good for them can often lead to collective insanity.

Or put another way, you can have a system where nobody is doing anything stupid. Everybody is doing what they think is sensible, but collectively it leads to a stupid outcome.

What I’m referring to here are ideas like externalities and the tragedy of the commons. At an individual level, an action might be perfectly rational, but once enough people behave the same way, the outcome for the overall system can be worse.

Anyway, I didn’t know that GPS systems like Google Maps and Waze essentially optimize at the level of the individual driver. They try to get you from point A to point B through what they think is the optimal route. But when you aggregate all these individually optimal decisions, you can end up sending a lot of traffic onto the same optimal routes, which then creates congestion and gridlock.

Air-traffic networks, by contrast, use network-aware routing, where routing decisions take the health and efficiency of the overall network into account.

What Google did is really clever. They took about 100 congested road segments across 10 U.S. cities, and then changed the route recommendations for about 2% of the trips in those regions. So instead of recommending the same route that Google Maps would typically suggest, which would have meant sending more drivers onto the same congested roads, it nudged a small fraction of them towards relatively underused roads with lower traffic, while keeping their travel times as close as possible to the fastest route.

In effect, traffic was taken away from a small number of already choked arteries and dispersed across a much larger number of roads that had more spare capacity.

And that tiny intervention was enough to produce statistically meaningful improvements: higher speeds on the targeted roads, slightly lower travel times across affected trips, and estimated reductions in carbon emissions.

Very interesting paper.

Hat tip to Yohan: