Not sure how much heat is directly contributed by cars. But regarding the original comment, having dirt or vegetation will be less heat absorbing than even white or gray asphalt. Also it helps with runoff amongst other things.
Even if cars directly aren't contributing all that much, the amount of empty parking spaces likely make their direct surroundings less hospitable than whatever the natural vegetation would contribute.
Even if cars directly aren't contributing all that much, the amount of empty parking spaces likely make their direct surroundings less hospitable than whatever the natural vegetation would contribute.