What causes a pothole?

What causes a pothole to develop? Learn here.

Potholes are formed by four different stages:

1. As tarmac ages it weathers becoming more porous and allowing water to enter the material. Over time traffic loads also cause cracks which can fill up with water.
2. During winter weather this water freezes and it expands as it turns to ice, pushing the tarmac upwards and outwards.
3. When the ice thaws and turns back into water it creates gaps or hollow voids in the surface of the road where the ice used to be. These gaps get bigger with each freeze-thaw cycle making the road weaker
4. When traffic travels over the tarmac it causes these voids to cave in, causing the formation of a pothole

Salting roads can make this cycle take place at a faster rate, because salt is designed to keep moisture on the road surface from freezing.

Road traffic also makes damage worse as more tyres roll over an affected section of road. This is why on some of our busiest roads a pothole can almost seem to appear overnight.

The recent freezing weather combined with last year's heavy winter and the floods of 2007 have really taken their toll on Gloucestershire's 3,300 miles of road.

Last year we repaired 38,000 potholes compared to 25,000 the previous year and we expect the number to be much, much higher for 2010.

To see how many potholes we have fixed since the start of Operation Road Rescue go to the Pothole progress tracker .