Truckers are ordering new equipment in record numbers, but are not turning to natural gas fueled heavy-duty trucks as fast as had been projected two years ago, according to a new report from ACT Research.

The rapidly declining cost of diesel is making the return on investment for adoption of natural gas less lucrative, according to ACT's “Natural Gas Quarterly." Original projections were that 2015 would see a 5% penetration of natural-gas-powered heavy duty trucks, but based on 2014 actual results and the sharp drop in oil prices starting in the fourth quarter of 2014, the report calls that optimistic.

“With the price differential between diesel and natural gas narrowing, the ROI to convert from diesel to natural gas is moving in the wrong direction: payback periods are lengthening,” said Ken Vieth, ACT senior partner and general manager.

ACT has developed a natural gas equipment payback index as a quick reference tool for fleets evaluating a switch from diesel to natural gas.