With the cold spell expected to last throughout this week, council gritters will now use a mix of road salt and grit on all roads outside Lerwick.
The SIC says lower levels of traffic means road salt is not being crushed and spread by passing traffic to activate it as it normally would.
It says using a mix of road salt and grit has a better chance of giving better traction, even with little passing traffic.
Grit is expected to be swept up from roads in springtime when the worst of the cold weather has passed.
With more vehicles on the roads in Lerwick, the council will continue to use salt on roads in the town for the time being.
Roads manager Dave Coupe said: “Forecasts suggest that we are in for another cold week ahead, with road surfaces across Shetland to continue to be well below freezing overnight.
“The ground is so cold that road salt will have only a limited effect.
“We’ve decided to use a salt and grit mix in most places, to help give better traction for vehicles in these cold conditions.
“Drivers should be aware of this and we’d ask them to drive with caution and reduce speeds to minimise the risk of stone chips from passing vehicles.”