Completely disagree with suggestion to use H4 on paved road. H4 shoukd NEVER be used on a paved surface, uphill or flat, especially not at high speed. It will result in increased steering effort making it impossible to evade an accident. Vehicle will not be able to fully turn and tend to go in a straight line.
Secondly at speeds above 30km/h and especially at highway speeds on a ROAD, H4 can cause permanent mechanical damage to the transfer case which can itself lead to an accident.
H4 should only be used on mud, sand, gravel, or other loose surfaces. It is safe to use at any speed as long as the surface is loose. To use 4x4 on a sealed surface, you need a "full time 4WD" vehicle which has a center differential along with the transfer case.
In short 4x4 is best avoided unless your vehicle is STUCK! Unnecessary use will increase chances of DEATH in an accident!
This information is also printed on the owners manual and warning stickers at drivers window and sunvisor.