It may be applied ahead of time when traffic is light and before rush hours hit. In contrast, a rock salt product needs to dissolve and become a brine solution before it starts to melt any ice or snow. Sand may require repeated applications due to windy conditions or being blown off the road by traffic. This means Maintenance Crews must stop doing other scheduled work in order to reapply it. In most areas after the winter season, sand has to be collected and hauled away for disposal or re-cycling, all of which adds to the cost.
Air quality is another part of the story.
Airborne dust is a health risk and there are limits to the amount of dust allowed in the air we breath. Some communities don't meet Federal Clean Air Act standards. Since sanding materials may help contribute to the problem when they get crushed and become airborne from traffic, using liquid de-icer is one accepted method to improve the safety of winter roads while limiting such airborne dust. In the Spokane metropolitan area, in heavy snow conditions, the Department still needs to use a certain amount of sand for its anti-skid properties. This sand, over time, is pulverized into dust along the roadways and becomes airborne.