The future of yellow school buses is green

School buses are the safest way to transport children to and from school.  However, pollution from diesel vehicles has health implications for everyone, especially children.

By reducing bus exhaust emissions, we can make sure that school buses are also a very clean way for children to get to school as well as provide clean-air benefits to communities throughout the state. 

By 2008, over 3,000 candidate school buses in our four-county area will be retrofit with diesel oxidation catalysts, diesel particulate filters and/or crankcase filter systems and will be using ultra-low sulfur diesel and/or biodiesel fuel.

Since 2003, Washington state’s schoolchildren have been the beneficiaries of one of the largest statewide, state-funded, voluntary school bus retrofit program in the country.  It provides enough funding over five years to retrofit three-quarters – 7,500 of 9,000 – of the state’s school buses.

The Puget Sound Clean Air Agency’s award-winning Diesel Solutions program laid the foundation for this state program.  So far over 1,800 school buses from 49 school systems in our agency’s four counties – King, Kitsap, Pierce and Snohomish – have been retrofitted.  And hundreds more will be retrofit in at least 58 Puget Sound-area public and private school districts before this program wraps up in 2008.   By fall 2006, all of these retrofitted buses are also using ultra-low sulfur diesel fuel, making them 50 to 90 percent cleaner, depending on which type of emission-control device has been installed.

In addition to the buses cleaned up under this statewide program, more than 75 school buses in three of our school districts – Everett, North Kitsap and Chief Leschi – were retrofitted prior to the start of the state-funded program using EPA funds. 

Most of the school buses have been retrofitted with oxidation catalysts, which can reduce fine particle emissions by 30 percent and toxic emissions by up to 50 percent.  Combined with the use of ultra-low sulfur diesel, now the standard on-road diesel fuel available nationwide this fall 2006, emissions are reduced by 50 to 70 percent.

Some of the buses around the region have been retrofitted with particulate filters, which can only be installed on newer buses.  They also require the use of ultra-low sulfur diesel fuel, so they could only be installed at districts who elected to switch to the cleaner fuel ahead of the federally mandated change.  The filters combined with the cleaner diesel fuel reduce emissions of fine particles, toxic hydrocarbons and carbon monoxide by up to 90 percent.

Retrofitting can also include the installation of a crankcase filter system on candidate buses to reduce the emissions that escape from the engine block into the bus.

However not all buses in a fleet are candidates for a retrofit, due to age, incompatible technology and other factors.  Because of the million-mile lifespan of diesel engines, these workhorses tend to stay on the road – and in our communities – for years.  Typically, when one owner upgrades to a new bus or truck, the equipment is sold to the next owner, and then to another, for perhaps 20 or 30 years.  And while the engine may still run, the technology is so old it can’t be retrofitted to operate more cleanly.  In these cases, we work with the school districts to target these buses for retirement to a scrap yard and replacement with a cleaner-operating bus. Some older vehicles can also be re-powered with a new, cleaner-running engine that is compatible with exhaust retrofit technologies.