Website that Freightliner has put up comparing the cost of fuel to operate a tractor on diesel vs. natural gas.
The Freightliner Cascadia 113 Day Cab tractor runs on the cleanest technology available: natural gas. Natural gas vehicles help fleets go green and add green to the bottom line. While the cost of diesel continues to rise, the cost of natural gas remains steady and significantly cheaper. Use the calculator below to find out how much money you can save by choosing Freightliner's natural gas lineup.Looks like based on their assumptions, the payback period of the additional cost to purchase the natural gas version of a comparable tractor like they have in their example is less than one year based on 50k miles driven.
Then the transportation company can start to reap over $20k annual fuel savings per vehicle (50k miles driven) over current diesel, while using natural gas the price of which is often regulated via local utility laws vs. the "free market" price of diesel.
This should catch on if the price of diesel continues to remain as high as it has and continue to erode US petroleum consumption.