Energy-Saving Raised Intersection Approach Lanes

Everyone enjoys roads, they provide valuable play areas for the world's children and put 10m of Asphalt between the idiots at No. 24 and me. However, when people are driving about on roads, they sometimes feel the need to be on a different, often perpendicular, road. This has forced the ugly compromise that is the intersection, with cars stopping and starting all over the place in a mesmeric orgy of wasted kinetic energy.

Now, should the road slowly rise on approach to the intersection... cars would be forced to trade kinetic energy for potential energy. The structure in question would be on the entry-to-the-intersection side of the road and similar to a long gentle speed bump, maximum height about 10cm. So, if the cars were slowing to a stop, then a portion of the kinetic energy would be converted to potential energy. Assuming the car is to resume movement, this potential energy will be regained as the car descends the small downhill section. If the car passes through the intersection without stopping, then the kinetic energy will be lost and regained pretty seamlessly.

Some considerations: the rise and fall cannot be too sudden... otherwise the benefit will be lost, heating the car's suspension.

Side benefit: when stationary at the intersection, you will be 10cm higher than normal. This is a useful aid to visibility.

Numbers: The kinetic energy of a 2000kg car at about 5mph is about 5kJ.

Raising that same car 10cm uses about 2/5ths of that. Meaning that about 2kJ is saved per car per (stopping)intersection.

There's about 1.3x10*8 J in a gallon of petrol. which is probably used at about 25% efficiency. Which means 1 gallon is saved for every 16250 car-junctions. Of course it won't work for more than say... the first 2-3 cars in a queue. So don't get all carried away with thoughts of energy independence.