You’d think that lowering the average speed on a road would make it safer to travel, but sometimes things aren’t that simple!
A team of statisticians from Spain and Poland measured the speed of cars at many places along a highway near Madrid, Spain.They found the average speed of traffic was close to the speed limit of 90 kilometres per hour for most of the day. However, when there were more cars on the road, especially between 6:00pm and 8:00pm, the average speed dropped to around 60 kilometres per hour.
If people are driving slower, then that should mean fewer accidents. It should also mean the accidents that do occur are less serious. But when the researchers checked accident statistics, they found the worst time for serious accidents was around 6:00 pm.
The researchers looked further into the traffic data and found that although the average speed had dropped, variation in the speed of traffic had increased. This means that on some sections of the road traffic was fast, while in other areas it was moving very slowly.
The researchers also noticed that the changes in speed were very sudden. Areas of fast and slow traffic were often only a few kilometres long. Along the length of the highway, traffic was speeding up and slowing down over and over again. With lots of sudden changes in speed, drivers would have to be very careful to avoid accidents.
The researchers have described how they measured the traffic, so the technique can be used on other roads. Once we know why our roads are unsafe, we can start to fix them. Hopefully, sometime soon, rush-hour will be a lot less dangerous.