AMES, Iowa - Two hybrid school buses that have hauled students around two Iowa school districts the past two years burned significantly less fuel than diesel comparison buses, but charging problems also kept the hybrid buses' electric motors out of commission for long periods of time, according to a recent report by Iowa State University transportation researchers.
The study found that a plug-in, hybrid-electric school bus operated by the Nevada Community School District achieved fuel economy 30 percent better than a comparison diesel bus that ran similar routes. A second hybrid bus operated by the Sigourney Community School District achieved fuel economy that was 36 percent higher than a comparison bus.
The buses, however, are the first generation of hybrid school buses and the Iowa road tests uncovered some maintenance issues. Both buses had problems with the charging system and that prevented the batteries from taking a charge. When that happens, the buses' electric motors don't operate and the V-8 diesel engines take over. So both buses worked routes for long periods without an operating hybrid system.
Shauna Hallmark, an Iowa State associate professor of civil, construction and environmental engineering and a transportation engineer for Iowa State's Institute for Transportation, said the fuel economy results look promising for hybrid school buses.
Hybrid technology is growing more common in cars and city transit buses. But it hasn't been widely available in school buses. And so Advanced Energy, a nonprofit corporation based in Raleigh, N.C., led an effort to bring the country's first 19 hybrid school buses to school districts in 11 states, including Iowa. The buses were built by IC Corp. and equipped with an Enova Systems Inc. hybrid-electric drive train.
Researchers at Iowa State's Institute for Transportation worked with Advanced Energy for more than two years to bring two of the hybrid school buses to Iowa. Researchers secured grants that paid for most of the $217,000 cost of each bus. The districts each paid about $70,000, the cost of a conventional bus. The project is also supported by grants of $220,000 from the Iowa Energy Center based at Iowa State; $120,000 from the New York State Energy Research and Development Authority and $83,000 from the Iowa Department of Natural Resources and the School Administrators of Iowa. The grant money also pays for a three-year study of the buses' performance.
Conducting the study are Hallmark; Robert Sperry, the Institute for Transportation's local roads safety liaison; and Abhisek Mudgal, an Iowa State graduate student in civil, construction and environmental engineering. They'll continue to study the fuel economy of the hybrid buses through May. They'll also conduct emission tests in the spring.
Improving the efficiency of school buses could have a real impact on school budgets and student health. Hallmark said school districts across the United States transport 24 million children over four billion miles every year. The country's 450,000 school buses burn 1.1 billion gallons of fuel annually and emit thousands of tons of pollutants.
But Richard "Scottie" Scott, the director of buildings and grounds and head of transportation for the Nevada Community School District in central Iowa, said the hybrid bus his district has been running isn't the cleaner, greener answer yet.
"It's had some problems," he said. "Overall, the concept is all right. But fuel mileage isn't what we hoped it would be. And there have been problems with the battery and connections. The hybrid wouldn't charge and wouldn't work."
Dan Taghon, the director of transportation for the Sigourney Community School District in southeast Iowa and the driver of the district's hybrid bus, said the bus worked well for the first 18 months. He figured mileage was about 10 miles per gallon, compared to the 12 miles per gallon that was expected, and the 6 to 7 miles per gallon of a standard diesel bus.
But, as the weather turned cold last fall, Taghon said the bus began having problems taking a charge. He said the manufacturer tried to fix the electrical system last month, but the problems are back.
"The cold weather must affect it," he said. "We just seem to have more issues in the cold."
Scott, Taghon and Hallmark said other issues that need to be resolved include developing a battery system that sustains a charge over longer routes, heating the bus interior when the electric motor rather than the heat-producing diesel is used in the winter and reducing tire wear caused by the extra weight of the hybrid system.
But, Scott said, "It's a start. Hopefully manufacturers can keep perfecting it and get it better."