Why is snow so bad for potholes?

WHO, WHAT, WHY?
The Magazine answers...

The freezing weather and snow causes even more potholes to appear in the UK's roads than usual. Why?

It will cost thousands of pounds, but it is a job Buckinghamshire Council says is vital and urgently needs doing.

How potholes are formed

As tarmac ages, it gets more porous. Rainwater penetrates cracks caused by constant traffic use.

When water freezes it expands. More cracks form and the tarmac is pushed outwards like a bubble.

The ice thaws creating voids, or gaps, under the surface. These get larger with each freeze-thaw cycle.

Traffic causes tarmac to collapse and form a pothole which gets larger as more traffic rolls over it.

BACK {current} of {total} NEXT

It is sending out extra teams to repair potholes in the road because more are appearing than normal this year. It's yet more money when so much has already been spent on grit to keep roads clear, but if the repairs aren't done it could cost even more cash in the future when the holes get bigger.

Potholes are not just a problem in Buckinghamshire, local authorities across the country are having to do the same. The repeated freeze-thaw cycle of the current cold spell, its timing and its length are being blamed for making the problem worse this year.

Potholes are formed by water penetrating the asphalt surface of a road through cracks caused by traffic. When temperatures plunge, the water freezes, expands and causes the surface to rupture. When the ice melts, it leaves a void below the surface, which caves in under the stress of vehicles and eventually forms a pothole.

"Snow and ice are the worst weather conditions for exacerbating existing road defects, due to the repetition of the freeze-thaw process," says Geoff French, vice president of the Institute of Civil Engineers.

'Quick fixes'

"A small crack has become a large crack, a large crack has become a small pothole and a small pothole very rapidly becomes a large pothole."

The timing and length of the current freeze - yesterday was reportedly the 24th in a row with snow on the ground and temperatures below zero in Scotland - have also made matters worse. Usually the weather for creating potholes arrives in February and March, when there is more rain. This year's snow means the water has arrived earlier. The length of the cold spell also means the water has had a chance to seep right into the foundations of the roads.

SEND YOUR POTHOLE PICS Email: [e-mail], subject POTHOLE MMS from UK: 61124 Don't forget to include your name and where your picture was taken Terms and conditions

"It would be difficult to predict how much road damage will be caused by the recent weather conditions, however we can expect a significant increase in pot holes," says Mr French.

Buckinghamshire Council is sending out six extra teams in addition to the nine it usual sends out at this time of year. It will cost £3,000 a week for each team.

"They will first of all work on a three-week programme and then probably we will be extending that," says a spokeswoman for Buckinghamshire Council. "We just need to get going on it straight away."

Mr French says long-term, preventative road maintenance is needed to properly address existing defects, rather than short-term "quick fixes".

"Such quick fixes are simply not effective in withstanding the sorts of conditions we have seen over the past few weeks and this is leading to more work and more cost. Maintenance backlogs are not being cleared but are continuing to grow - and will grow even more with the latest round of snow and ice."

'Vital asset'

Based on current local authority budgets it would take an estimated 13 years to clear the backlog of pothole repairs in England and 15 years in Wales, says ICE. Its calculations are based on 2009 figures from the Annual Local Authority Road Maintenance Survey.

"I'm sure local authorities would say this is because insufficient money has been given to them to carry out the preventative, long-term maintenance that is required," says Mr French.

Whoever is to blame, what is clear is that the issue of potholes needs to be tackled at a national level, he adds.

WHO, WHAT, WHY? A regular part of the BBC News Magazine, Who, What, Why? aims to answer some of the questions behind the headlines

"It's become clear in the last few weeks and months that roads are vital to our current way of life, you only need the absence of something to appreciate how much you need it. Roads are being used more and more intensively as time goes on, so roads are a vital asset that need to be treated as such and maintained."

During the cold snap in February last year there was an estimated 40% increase in road damage, according to the AA. It says its insurance branch received more than three times as many claims for pothole damage than the same month the year before.

Local authorities are urging people to report potholes. This can usually be done via council websites. There are also a number of other websites offering advice on dealing with and reporting potholes, including potholes.co.uk and fixmystreet.com.