Don’t panic. Give the car a little gas to let it rid itself of some engine heat. Turn on the heater, which will draw heat from the engine. If the gauge is firmly in the danger zone, pull to the side of the road and let the motor cool. Most cars shouldn’t overheat–so have the cooling system checked. The problem could be anything from a clogged radiator core to low engine coolant to an inoperable radiator fan.