It would require the car carry the salt, which isn't light.

If everybody did it, it could oversalt the road.

Best leave it up to the professionals that control how much salt is applied, and have the equipment capable of carrying and properly distributing the load of salt they need.

Most people are too cheap to buy salt for thier own sidewalks. I can't imagine anyone buying enough salt to salt their way to the grocery or work each time it snowed. Also, cars and light trucks are ill equipped for carrying the loads required to be effective.

If your idea is to have the municipality buy it and make it available to the public it won't work because there isn't enough room for everyone's car to be at the maintenance facility (central location where they store the tons of salt that go out each storm) at once. The traffic problems would be tremendous.

Here we average 80 tons of salt per snowfall. The salt is metered by the trucks at 300 pounds per lane mile. The trucks plow as they salt so the salt is more effective as there isn't as much snow to melt then.

That's just a few of the reasons this isn't such a good idea.

Salt dispensing is the wrong answer anyway.

Getting the snow off the road would be better, like with electric roads or a jet-engined melter. Salt destroys cars and doesn't work when the temp's below say 10F, which is when I'm driving to work.

I live in a rural area and routinely drive my rear-drive car on un-salted and even un-ploughed roads.

I also agree with the points by classicsat and Hyenuf

Dispensing salt from your car will help only the guy who is following you. If you're the first guy on the road, you're out of luck.