Every day, 25 million children in the U.S. spend an average of an hour and a half on public school buses to get to and from school.School districts and health advocates have recognized the importance of reducing students’ exposure to harmful diesel exhaust emissions. There are now more than 150 school districts operating approximately 5,500 natural gas powered vehicles in their fleets to safely transport students and to help improve the air quality of these students. These school districts are also enjoying reduced fuel and maintenance costs with buses than have proven to be on par with diesel buses in terms of their durability, performance, and safety.
Natural gas school buses provide significant environmental benefits compared to diesel-powered school buses. The most recent analysis, which takes into account the emissions of the upstream production and distribution of natural gas, new natural gas buses produce 13 percent fewer greenhouse gases (GHG) and 16 percent fewer nitrous oxides (NOx) compared to new diesel buses that require maintenance-intensive particulate filters and DEF systems. Natural gas buses achieve these figures using maintenance-free three-way catalyst exhaust systems. When comparing the environmental benefits of natural gas buses to in-use diesel buses, the benefits become even more drastic.
Emission Reductions (%) of New Natural Gas School Buses Compared to In-Use Diesel Buses 2002 2007 GHG 25 25 NOx 92 76 PM10 98 21
Both Thomas Built and Blue Bird provide factory-built Type D natural gas-powered school buses. Both manufacturers use the Cummins Westport 8.9L ISL-G engine, which is available in different HP/torque selections. These buses are available through the standard dealer network. There are also a number of options to retrofit new buses or reposer buses already in use.
Cummins Westport is currently developing the 6.7L ISB-G engine that will expand the availability of medium-duty natural gas school buses. This engine is scheduled to become available in 2015. Bright yellow buses may be the most visible NGVS in school fleets, but school districts also are deploying natural gas powered sedans for their healthcare, social services and other central administrative staff, and pickups and vans for their facilities and maintenance personnel. Some districts are even driving home their message of environmental responsibility with students by using NGVs in their driver training programs.
Making the switch to natural gas vehicles is made easier where a public CNG fueling station is located nearby, as long as the station’s equipment is capable of accommodating the additional load. Another consideration is the proximity of the station to the central bus depot or to the bus routes, and the convenience and cost of driver time spent traveling to and from an offsite fuel site. If use of existing fueling infrastructure is not practical, convenient, or economical, it may be better to build a new station on-site or nearby. School districts have the choice to fuel their CNG vehicles with fast-fill systems, time-fill posts, or a combination of both.
While fast-fill CNG stations provide fueling capability similar to gasoline and diesel dispensing rates, fleets that return to central depots for extended periods—such as overnight or long mid-day breaks in service—may find time-fill fueling systems more attractive. These systems are considered the most efficient and economical because they do not require as much compression capacity as a fast-fill system, and they do not require on-site CNG storage or fast-fill dispensers. In time-fill applications, drivers connect their vehicle to the automated system and walk away. The fueling apparatus automatically shuts off when the vehicle’s fuel cylinders are full. The automated nature of time-fill fueling reduces as much as 15 minutes of labor time per driver per day.
There are a number of OEM options for school districts. For more information and a complete list of EPA and CARB certified vehicles and engines, visit the Vehicle Availability page.
The U.S. Department of Energy’s (DOE) Alternative Fuels Data Center (AFDC) provides an online tool that lists available alternative fuel vehicles from leading OEMs. To view a list of natural gas school buses currently available, visit the Alternative Fuel and Advanced Vehicle Search.