A free recorded webinar sponsored by the Propane Education & Research Council provided the perspectives of two student transporters on the the effects of propane school buses in their fleets.
Michael Taylor, PERC's director of autogas business development, revealed that propane was the most preferred alternative fuel in the world, with 27 million vehicles in use worldwide and 220,000 in the U.S.
Four school bus manufacturers — Blue Bird, Collins Bus, IC Bus and Thomas Built Bus — offer propane options. Taylor added that 830 school districts in 48 states are seeing savings of up to $22 million per year by using propane to fuel transportation efforts.
“Propane affords significant benefits over diesel and gas with respect to fuel costs, maintenance and greenhouse gases,” Taylor declared. He pointed out that propane is reliable even in cold conditions, warms up rapidly and provides consistent heat throughout the bus.
“And there is funding available for it,” he added. Money will be allocated to propane through the Volkswagen Mitigation Trust Fund, which provides more than $2.7 billion for reducing NOx emissions. Propane is one of the fuels states will specify as allowable projects under the program.
Taylor gave the example of Texas, which could reduce NOx by 7.5 million pounds per year if it replaced its almost 22,000 diesel school buses older than model-year 2007 with propane buses.
Calculating Cost Per Mile
The Clear Creek Independent School District fleet in near Houston is comprised of diesel, propane, gasoline and CNG buses. Diesel makes up the majority of the fleet and propane accounts for about 18 percent, said Fleet Manager Ken Winters.
He shared during the live webinar on March 30 that grant funds paid for infrastructure and 50 percent of the purchase price of each propane bus, and that the fuel tax credit has been helpful. “But if we just had to buy the bus outright, yes, we would still purchase propane if we had to pay 100 percent of it,” he stated.
Winters said that the district’s latest diesel buses were purchased last year, and they average only about 5.7 miles per gallon, which surpasses the mpg of propane. But Diesel Exhaust Fluid (DEF) is a cost many fleets don't consider, at least initially, he said. Winters said DEF adds six to nine cents to Clear Creek ISD's per-gallon cost of diesel.
Brian Swestka is director of transportation for Iowa's Howard-Winneshiek Community School District, a rural district with the third largest service area in the state. About 80 percent of the district’s school bus routes operate on gravel roads at some point during their routes, so “schools are getting real creative to save money,” he added.
He said the district's propane buses “are performing flawlessly in the rural environment.” The seven propane buses get four to five miles per gallon while the district's 16 diesel buses get five to eight miles per gallon.
He also advised the audience to divide fuel cost by miles driven to identify the cost per mile, which he said is a more useful measurement than cost per gallon of fuel or mpg. In Swestka’s fleet, diesel buses cost 80 cents per mile to operate, compared to 19 cents per mile for propane buses.
Swestka then presented the example of two identical 2017 model-year school buses in his district. The propane school bus operates is on a stop-and-go route and does not get as good mileage per gallon as the diesel bus, he commented. But the propane bus costs 30 cents per mile to operate while the diesel bus costs 40 cents per mile. “It adds up pretty quick,” he added.
Considering the Total Cost of Ownership
Winters identified a major problem with diesel engines, namely that they require a minimum average speed of 19 miles per hour for optimal regeneration of the engine to clear soot from the Diesel Particulate Filter (DPF). He added that this speed is one that most school bus route, especially in urban or suburban areas, often do not reach. Issues with low speeds and low engine RPM then lead to particulate matter and soot buildup, which in turn leads to costly engine problems. The engine can even overheat so much that the school bus just shuts down.
DPFs and Diesel Oxidation Catalysts (DOC), turbos, actuators, exhaust temperature and pressure sensors, exhaust gas recirculation systems, and intercoolers are all diesel engine components that are not necessary in propane buses, he explained. Measuring and treating exhaust can run costs into the tens of thousands of dollars.
When these additional repairs are added to fuel costs, the total cost of ownership for diesel buses continues to mount. “Diesel right now is just killing our parts budget,” Winters said.
Swestka agreed: “Repairs need to be made and you can’t cut corners on safety."
An added expense is paying drivers to take buses on long drives at higher speeds to trigger engine regeneration. Also, for Winters’ operation, replacing a propane engine costs half as much as replacing a diesel bus.
Taylor, meanwhile, cautioned that districts must consider more than just visible costs related to initial purchase, insurance, state inspections, fuel, warranty and maintenance. There are hidden costs like repairs, downtime, environmental impact, disposal and labor.
“Compare the hidden costs and you will find propane provides the lowest total cost of ownership,” Taylor said.
User Experiences With Propane
Winters said that propane provides a better user experience for both transportation employees and community members. He said that the smell of diesel gas is more noticeable in the bus yard after using the comparatively odorless propane, and that concerned citizens still complain about black clouds of exhaust from the older diesel buses but never about the propane buses.
He identified longer trips or field trips as an area where diesel buses have an advantage since there are just more diesel fueling stations in the country, and said that he outfitted some of his propane buses with 96-gallon tanks to help with that.
The familiarity of technicians and drivers with diesel is a barrier to propane adoption, Winters said, but he added that training helps overcome such resistance to change. For example, drivers had to be trained to “feather” the throttle on propane buses to increase mpg because they were used to “mashing” the throttle on diesel buses.
Federal Assistance and Standards
Swestka shared that, during fiscal year 2016-2017, his propane cost was 51 cents per gallon, compared to $1.79 per gallon for diesel.
Federal tax credits good for 36 cents per gallon of alternative fuel and 30 percent of alternative fueling infrastructure are no longer in effect as of the end of last year, but Taylor said that lobbying for such benefits continues.
This year, propane was also added to the California Air Resources Board (CARB) heavy-duty onboard diagnostics (HD-OBD) regulation, which previously only applied to diesel and gasoline engines. CARB recently certified ROUSH CleanTech’s propane autogas school bus drivetrain as meeting that standard.
However, exhaust emissions standards going into effect in 2024 will heavily impact diesel, said Taylor. CARB is stringent but EPA is getting just as strict, he added.
“We see propane autogas becoming more competitive,” Taylor said. “The decisions you make today, you’re going to live with for a long time. Do your due diligence. Compare the fuels. Low bid today may mean high costs tomorrow.
- Visit www.propaneschoolbuses.com for more information and resources from the Propane Education and Research Council.
- See the 2018 STN Buyer’s Guide for information on available engines and powertrain options for school buses.
- Register for this year’s STN EXPO, where a panel discussion will focus on the topic of alternative fuels in school bus fleets.
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