From a great height, you might think that cars look like ants, but sadly commuters have yet to master insects' sophisticated traffic management. By forcing ants into increasingly crowded environments scientists have studied how they avoid congestion, potentially helping improve human traffic as well.

The way ants move in formation is so recognizable it is immortalized in children’s songs, yet we know surprisingly little about how they manage it. Dr Laure-Anne Poissonnier of Toulouse University decided to change that with an experiment that tempted ants across a bridge to see how well they navigated the scrum, reporting her findings in eLife. 

Possoinier placed food across a bridge from Argentine ant (Linepithema humile) colonies with between 400 and 25,600 members. The width of the bridge was altered to create 170 combinations testing the ants' response to changing circumstances.

The results demonstrate that despite, or perhaps because of, their tiny brains ants are much better than us at moving in crowds. Traffic flow was maintained when 80 percent of the bridge was occupied. Previous experiments have shown humans, whether on foot on in cars, tend to lose speed at 40 percent occupancy or above.

“At low densities, there is a clear linear relationship between ant density and the flow, while at large density, the flow remains constant and no congestion occurs,” Dr Poissonnier and colleagues wrote in the study.

Given the multi-billion-dollar cost of traffic congestion to large cities, the ants' hints would only need to provide a few percent benefits to be immensely valuable.

Poissonnier found ants adjust their speed of motion depending on density. Moreover, as space gets cramped they increasingly avoid interactions. Although these encounters transmit information, they hold up traffic behind the interacting ants.

One reason human traffic can get so bad is that each constituent has individual goals, which may not align with the common good. Attempts to adjust human behavior, for example through congestion charges, are often fiercely resisted even in the face of overwhelming evidence of their benefits. As Poissonier notes, ants’ goal is collective.

The researchers note ants are one of the few animals besides ourselves that engage in two-way traffic. Other animals, such as fish or bison, move on mass, but they do so in one direction at a time, avoiding the need to divide available space to prevent head-on collisions.

Ant species may have evolved different traffic management solutions to suit their lifestyles. Previous studies have usually been done at lower densities than Poissonnier investigated, but nevertheless revealed leaf-cutter and fire ants lower their speed as density rises, while wood and mass raiding ants manage to maintain constant speeds within the ranges studied.

It is possible self-driving cars may one day be programmed to act collectively, smoothing traffic flow. Having several ant approaches to draw on could facilitate this.