Heavy-duty natural gas powered vehicles (NGVs) that meet strict emissions standards are more cost-effective to own, operate and maintain over their lifetime than comparable diesel powered vehicles when the price of crude oil is more than $US31 per barrel, according to a national report prepared by TIAX, a product and technology development firm, for the California Natural Gas Vehicle Partnership.

Oil prices have been well above $31 per barrel for some time.

"The findings of our report are significant," said Mike Jackson, of TIAX.  "Transit, refuse, and short-haul fleet managers should carefully evaluate natural gas and diesel vehicle technologies that meet 2010 emissions standards. For these applications, our study indicates vehicles equipped with stoichiometric natural gas engines and three-way catalysts will have similar owning and operating costs compared to diesel engines equipped with advanced after-treatment technologies, which enable both sets of vehicles, respectively, to meet new emissions standards.

"That said," Jackson added, "at oil prices above $31 per barrel, natural gas technologies are cheaper than the diesel alternatives and may well be the best overall option for fleet managers."

Projections of diesel vehicle costs have "a higher range of variation" than natural gas vehicle costs due to "uncertainty in the diesel engine technology and emission control equipment needed" to meet the performance demands of 2010 heavy-duty applications, according to the report.

Gunnar Lindstrom, chairman of the California Natural Gas Vehicle Partnership, a coalition of public- and private-sector interests that commissioned the report, welcomed its findings. "Diesel engines have had a significant cost advantage over natural gas up to now, but the costs of owning and operating comparable vehicles that meet 2010 emission standards, coupled with the price of petroleum, shifts the advantage to natural gas. What's more, natural gas vehicle manufacturers are now taking orders for vehicles that meet 2010 emission requirements, while uncertainties remain about diesel vehicle costs and technologies.  This is solid justification to increase deployment of natural gas vehicles in California and across the country."

Lindstrom added that natural gas for US transportation is primarily sourced domestically, so increased adoption of NGVs heightens the nation's energy security by decreasing reliance on foreign energy sources.

Todd Campbell, policy and science director for the Coalition for Clean Air and the environmental organisations' representative for the partnership, has been closely involved in California issues related to mobile sources and air pollution. Campbell said: "With anticipated increases in population and vehicles on California's roads, reducing tailpipe emissions is more important than ever.  We're hopeful that this report will encourage more fleet operators to deploy low-emission vehicles powered by natural gas. It's an important step to help assure clean air and a high quality of life."

The report, "Comparative Costs of 2010 Heavy-Duty Diesel and Natural Gas Technologies," estimated the life-cycle costs for heavy-duty diesel and natural gas vehicles that meet the stringent 2010 EPA and California Air Resources Board emission requirements. Refuse haulers, transit buses and short-haul trucks were analysed.

The study is based on a life-cycle cost model that incorporates expected vehicle, fuel, operational and maintenance costs during a vehicle's lifetime, and then varied several factors independently.  Among them were the cost of crude oil per barrel, the choice of diesel exhaust gas after-treatment systems, the price of natural gas versus diesel, the price of liquefied natural gas versus compressed natural gas, engine costs and fuel economy.