ST. PAUL — Cities across Minnesota are turning to spraying a saltwater solution on roads to help keep them ice-free, with some saying it’s more environmentally responsible than spreading rock salt.

The Minnesota Department of Transportation has added brine sprayers to its fleet of 840 snowplows. Ramsey County almost tripled its salt-spraying capacity last winter.

“More and more communities are using the liquids,” said Brooke Asleson, who manages programs to encourage salt spraying for the Minnesota Pollution Control Agency.

Asleson said spraying saltwater before a storm cuts the amount of salt on roads and reduces the amount of salt polluting rivers and lakes.

“It’s great win for the environment,” she said.

Almost all the salt put on roads was dumped by snowplows using rear-mounted salt spinners, until recently. The only brine used was stored in saddle tanks on the sides of snowplows and sprayed along with the salt.

Oversized clumps of salt often would bounce on the roads, scattering in the wind, Asleson said. The lack of predictability and control would lead to plow drivers applying too much salt, she said.

Brine-spraying trucks go out 24 to 48 hours before a storm and apply a thin coat of the salt mixture, which acts immediately on snow and ice and creates a barrier to prevent any new precipitation from sticking. The spray can be precisely controlled, Asleson said.

As a snowstorm loomed over the Twin Cities last Friday, truck drivers huddled at Ramsey County’s maintenance building in Arden Hills and pored over weather reports to pick the best strategy.

“You could get just cold, then snow,” said Bob Trick, assistant general supervisor of the county’s maintenance and construction department. “Or you could get rain, then warm, then freezing rain. Or 2 inches of snow and freezing rain.”

Some of the county’s four salt-spraying trucks are converted pickup trucks with 500-gallon tanks in the beds. But in 2017, the county bought two $200,000 spraying trucks, each with almost four times that capacity.

“These improve safety, and the removal of anything we have to plow,” Trick said of the two huge trucks that spray saltwater before storms arrive, so ice never has a chance to form.

Trick and the drivers had to consider whether rain was in the forecast, since rain would wash away the salt; what kind of salt to use, depending on the temperature; and whether to hit just “hot spots” or every road.

On Monday, Trick said the snow removal went smoothly, thanks to the new salt sprayers and the county’s fleet of 48 snowplows.

“It’s a judgment call,” he said. “You play it minute by minute, hour by hour.”