Motorists are being advised to check road conditions before setting off as heavy, thundery showers are due across southern England this weekend.
The Met Office has warned of heavy showers in Devon and Cornwall with possible torrential downpours extending to Dorset, Hampshire and Somerset.
There is also a risk of further showers in parts of the South East overnight.
Showery rain with perhaps some thunder is forecast for Saturday in southern England, the Highways Agency said.
A spokesman from the agency said: "Rain and spray can reduce visibility and when the road is wet it can take up to twice as long to stop so it makes sense to slow down when it's raining.
"If your vehicle loses its grip take your foot off the accelerator to slow down.
"Don't brake or steer suddenly because you will have no control of the steering or brakes.
"Surface water may affect motorways and major A-roads so we advise drivers to move slowly through any standing water and test their brakes once they're through before continuing to drive." The agency has also advised that drivers carry extra clothing and an emergency pack, which includes food, water, a raincoat and a torch.
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BBC NEWS | England | Drivers warned over bad weather