You can model this as an increase in the supply curve. Price goes down, quantity demanded increases.
The New Yorker has a nice essay on what they call The Efficiency Dilemma:
The problem with efficiency gains is that we inevitably reinvest them in additional consumption. Paving roads reduces rolling friction, thereby boosting miles per gallon, but it also makes distant destinations seem closer, thereby enabling people to live in sprawling, energy-gobbling subdivisions far from where they work and shop.HT: Hoyt