According to ACT Research, U.S. and Canadian natural gas Class 8 truck retail sales improved modestly in February.

ACT attributes the improvement to a high number of natural gas vehicle repeat sales, despite the continuing low cost of diesel prices, which is making the return on investment for adopting of natural gas less lucrative for fleets not yet invested in natural gas-fueled vehicles.

“With the fuel price differential continuing to narrow, the ROI to convert from diesel to natural gas is moving in the wrong direction: payback periods are lengthening,” said Ken Vieth, ACT’s senior partner and general manager. “This doesn’t mean the adoption of NG fuel has stopped or that there are no new developments supporting a future uptick in NG truck orders.

Vieth said that despite a 3% month-over-month uptick in February, year-to-date volumes are 14% below 2015’s level and year-over-year sales are down 25%.

“NG infrastructure continues to be built, albeit at targeted locations, and existing NG equipment users remain committed to its long-term viability and emission benefits,” said Vieth.

ACT Research expects modest, single-digit growth for the adoption of natural gas as a transportation fuel in the U.S. the next few years, barring legislative changes.