Between 2017 and 2019, the Land of Enchantment Clean Cities Coalition (LOECC) compared the fuel economy and cost-per-mile of four-identically sized and powered mid-sized transit buses operating on three alternative fuels – natural gas (CNG), propane/autogas (LPG) and ethanol (E-85).
The three alternative fuels were compared for economy and performance to a “baseline” unleaded-gasoline bus. The analysis equated the vehicles using 38,500 miles per year and average fuel costs (with and without incentives) as well as maintenance and life-cycle costs. The four buses had identical engines and chassis and similar service duty-cycles.
Note: Alternative fuels are defined in the Energy Policy Act as natural gas, propane, ethanol, hydrogen and electricity. LOECC knows of no other such side-by-side transit fleet comparison reported in the U.S. The four-vehicle fuel and performance data include the cost of fuel, gallons consumed, miles driven, engine/fuel system maintenance, original vehicle cost and grant/incentive discounts for alternative fuels and vehicles.
Two of the fuels were gaseous, CNG and LPG, which are equated to gallons on an energy basis using gasoline equivalence and emissions as baselines.
Propane is sold by the gallon but gaseous when vented. The propane gallon contains roughly 25% to 30% less energy than a gasoline gallon, which is compensated for in the analysis.
Natural gas is compressed to a high pressure and dispensed and tracked in units of gasoline gallon equivalence (GGE).
Ethanol (E85) is a liquid fuel but contains approximately 25% to 30% less energy per gallon compared to a gasoline gallon, so one gallon of E85 takes you roughly 3/4 of the distance compared to a gallon of gasoline.
The data collected from North Central Regional Transit District (NCRTD) were reported to the U.S. Department of Energy (DOE) over two-consecutive years for annual alternative fuel data review (2018 and 2019).
All fuel and engine comparisons were verified for accuracy using the following sources:
1) Ford 6.8-liter engine and fuel specifications
2) U.S, Environmental Protection Agency (EPA) fuel/emissions certifications
3) DOE fuel and emissions research
4) Clean Cities national fleet studies
The vehicles were also analyzed for the greenhouse gas (GHG) emissions, using Argonne National Laboratory’s AFLEET calculator that compares gasoline, propane, natural gas, as well as diesel and electric vehicles on a life-cycle greenhouse gas emissions.
The article includes information related to alternative-fuel dispensing-equipment options and a federal tax rebate that is available to public entities on a gallon- dispensed basis, as well as vehicle rebates (>$5,000) and fuel discounts from vendors.
With and without incentives, propane autogas had the lowest cost-per-mile and emissions among the four vehicles analyzed over a two-year period as well as on an estimated life-cycle cost analysis. Liquid-injection propane fuel systems are easy to maintain and extremely safe with millions of miles of accident-free bus service as proof. Further, propane is the most used rural domestic fuel with the widest distribution network of any alternative fuel in North America, making it an ideal fuel for New Mexico mid-sized transit fleets.