Gritters have been dispatched onto UK roads as the country heads into a cold snap.

Here the PA news agency answers seven key questions about the vehicles:

– What are gritters?

Vehicles that spread rock salt.

– What does the salt do?

When it is spread before road surfaces drop below zero degrees Celsius it minimises the chances of frost or ice forming.

– How about snow?

Salt does not stop snow from settling on road surfaces, but it makes it easier for the snow to be removed.

– How many gritters exist

National Highways – which manages motorways and major A-roads in England – has 535 gritters based at 128 depots.

The Local Government Association said councils in England – which manage local roads – have an average of eight gritters and three pieces of related equipment such as snow blowers, tractors and quad bikes.

– How much salt is there?

The Local Government Association said councils in England have stockpiled a total of 1.4 million tonnes of salt.

National Highways has more than 280,000 tonnes of salt stored in barns at the start of each winter.

– Is that enough?

It depends on how bad the conditions are over the winter, but there are currently enough supplies for all gritters.

– Has the cost of salt increased?

English councils said the price of gritting salt has risen by an average of 2% in the past 12 months.

Five authorities reported increases of more than 10%.