Ok! This is my worst idea. I always thought transportation itself could be made less expensive by making use of gravity to make stuff move down on their own. For example, imagine you have a path 2 kms long and a truck that has to travel that. Now imagine a special "UPLIFTER" machine (basically a big electrically powered, mechanical floor) at the beginning of that path which, when the truck is on it, lifts it up to say 200 mts high and then leaves it on a slope to slide through that 2 km path without spending any energy/fuel, just leaving everything to gravity. My idea was that it would cost lesser to lift a vehicle to 200 meters height than the cost of amount of fuel needed for the vehicle to travel that distance. Now imagine all the two-way highways have such 'uplifter's at 2 km stretch which continuously uplift the vehicles to a height which would then come down travelling on the slope till the next uplifter.!! I know I know, forgive me.