Question

why steam engine is not used in any vehicles.

Answer 1

because if they were used then after every mile we have to put coal in the engine which is not possible ........

hope it helps

Answer 2

Steam engines use coal as their fuel which causes pollution. Also incomplete combustion of coal produces carbon monoxide which is a poisonous gas. Indiscriminate use of coal will reduce the quantity of coal for future generations.
Hence we should use engines which run on electricity or petrol.