Why do I see a lot of fire trucks and ambulances with chains hanging at the bottom and dragging the roads?

Question

Why do I see a lot of fire trucks and ambulances with chains hanging at the bottom and dragging the roads?

Answer 1

They are chains for snow/ice conditions.

The chains are air-actuated; A wheel is mounted horizontally and rubs against the sidewall of the tire causing it to spin.

Small lengths of chain are attached around the wheel and hang down, so when the wheel spins it swings the chains out and they go underneath the tire, giving it more traction.

You will see grounding chains or metal braided straps that drag on the ground on fuel tankers... Those are for actual grounding of static electrcity.

Answer 2

That's to equalize the static charge that can build up on the vehicle.  The static isn't dangerous to people, but it could fry sensitive lifesaving equipment aboard the vehicle under the wrong conditions.