Further measures to conserve salt supplies are likely to be brought in later this week as more snow is forecast for the UK.
Motorists are continuing to face tough conditions as authorities cut down on gritting as supplies deplete.
The Highways Agency and local authorities have cut salt use on roads by some 25%.
Tom Foulkes, director general of the Institution of Civil Engineers, said: "National salt supplies are now running dangerously low.
"In future, we must have much better contingency plans in place to ensure our roads are not rendered unusable when snow hits."
And the wintry weather looks set to continue for the next few days before a slight thaw sets in as the mercury begins to rise later in the week.
Billy Payne, a forecaster with MeteoGroup, the weather division of the Press Association, said milder air pushing into the UK from the Atlantic would cause more heavy snow today and tomorrow as it bumps into the colder air over the country.
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