Rush-hour drivers shun shortest routes - but should they?

Queuing traffic

Rush-hour traffic jams are a daily bind for many commuters, but are drivers making them worse by trying to avoid them?

A study of four major world cities has found drivers in peak-time traffic often avoid taking the shortest route to their destination.

Drivers may think the most direct route will be too congested or have too many intersections or traffic lights to be the quickest.

While this might hold true most of the time, analysis of rush-hour traffic patterns in Anaheim, USA; Winnipeg, Canada; Isfahan, Iran; and Barcelona, Spain found the shortest routes are generally less congested than the alternative routes drivers take – and may even be faster.

Counterintuitive pattern

Professor Ernesto Estrada, who conducted the study at the Department of Mathematics and Statistics of the University of Strathclyde, with colleagues from Isfahan University of Technology in Iran, said: “We found that rush-hour traffic in major cities across the world follows a strange and counterintuitive pattern.

“Instead of drivers navigating the city by using the shortest paths to their destination, they travel in a diffusive way. Our study suggests drivers perceive the shortest routes as ‘too central to be empty’ and avoid taking them altogether.

“It may be true the quickest route to a destination is not via the shortest path, but when everyone decides this and takes alternative routes making them more congested than the shortest route, does that still hold true?

“Because drivers mainly rely on cognitive maps they have previously created to navigate the city, they end up using the same routes to get to their destination. The result is the creation of what we call ‘communicability’ routes that become more congested than the shortest path and possibly we will have to wait more due to congestion than to traffic lights, signals and intersections.”

The study, published in the journal Nature Human Behaviour, provides insights into how information flows along complex networks and could help city planners tackle traffic congestion.

In their paper the scientists theorised which routes a larger proportion of drivers would take at rush hour. They then validated their findings with empirical data about the traffic at rush-hour in the four cities.

They found, for example, that in Anaheim there is 35% more traffic through the ‘communicability’ routes than through the shortest paths connecting thousands of origin-destination pairs in the city.

Professor Estrada said: “The study of vehicular traffic flow in cities offers a unique opportunity to test theoretical models about network flows using experimental data.

These findings are very important for managing traffic in cities and proposing measures that alleviate congestion at busy times.

“It may also have implications far beyond the aims of this study, and may influence the way in which we understand network flow in general, for example in the brain where most of the processes are diffusive because it is made of 70 per cent water.

“But many scientists studying brain networks still consider that information flows through the shortest paths connecting different brain regions.

“We are now working on generalising these findings for a better understanding of complex networks in general.”