(The Conversation) – Each weekday, more than half of the K-12 students in the U.S. – over 25 million pupils – ride a school bus. Until very recently, nearly all of these 500,000 buses ran on diesel fuel.

Nationwide, diesel-powered school buses produce more than 5 million tons of carbon dioxide emissions. They also generate air pollutants that are harmful to children’s health – especially fine particulates. Studies show that exposure to diesel tailpipe emissions worsens respiratory conditions, decreases lung function and can lead to increased hospital admissions and emergency room visits.

Shifting to cleaner buses is especially important for low-income students. Across the U.S., 60% of low-income students ride the school bus, compared with 45% of other students. School buses often idle their engines while they are loading or unloading, which exposes children directly to exhaust fumes.

I study issues at the intersection of infrastructure, policy and place, including sustainability and equity in transportation. While electrifying school bus fleets requires big investments, I believe the evidence makes clear that it will more than pay off over the long term in health and economic benefits, and I am encouraged to see public and private investments moving in that direction.

Early movers

Decisions about switching from diesel to electric school buses typically lie with cities and school districts, although state governments are getting involved. As of March 2022, 415 school districts or contracted fleet operators had committed to deploy 12,275 electric school buses in a wide range of settings, from large cities to rural counties, across 38 states and lands of two Native American tribes.

California, a longtime leader in clean vehicle policy, acquired its first electric school buses in 2014. Now the state is spending nearly US$70 million to replace more than 200 diesel buses with electric versions to advance its climate and air-quality goals.

Another notable case is Montgomery County, the largest school district in Maryland, which is replacing 326 diesel buses with electric buses by 2025 and building five charging depots. The district serves a diverse population of 160,000 students in 210 schools.

In Virginia, the utility company Dominion Energy announced in 2019 that it would provide 50 electric buses for 16 school districts across the state as one of its initiatives to reduce pollution and promote sustainability. Dominion is paying for infrastructure costs and absorbing the cost difference between a diesel and an electric bus.The town of Chesapeake, Va., takes delivery of its first electric school buses, funded by the utility Dominion Energy.

The biggest obstacles: Funding and space

As Dominion’s gesture suggests, converting bus fleets isn’t an easy step for many school districts. An electric school bus can cost up to $400,000, two to three times the price of a diesel bus.

But electric buses have lower operating costs, so they save districts an estimated $4,000 to $11,000 per bus per year compared with diesel versions. That can make the costs of electric buses comparable over their lifetimes.

Electric bus motors have about 20 parts, compared with 2,000 in a diesel engine, and require far fewer maintenance steps such as regular fluid changes. And because many of their mechanical systems, such as braking and steering, are similar to those in diesel buses, electric buses are relatively easy to service, especially in districts where both bus types operate.

Charging stations also require money and space, especially in areas where bus routes are long and battery range is a constraint. Most buses now on the market have ranges of about 100 to 120 miles (160-190 kilometers) on a single charge.

In a 2013 study, analysts at the National Renewable Energy Laboratory reviewed school bus drive cycles in Colorado, New York and Washington and found that the average school bus was typically in operation for 5.26 hours per day. Driving distance averaged about 32 miles, (50 kilometers), with some buses traveling over 127 miles (200 kilomaters) daily.

School districts need places to charge buses easily and efficiently, especially between morning and afternoon routes. Building this infrastructure, especially as diesel buses continue to operate concurrently with growing electric fleets, can pose a challenge in school districts where space is limited.

Buses as power sources

At the same time, charging infrastructure can make school bus fueling and management more efficient. Today’s managed charging infrastructure allows districts to plug in a bus whenever it is parked at the depot but have the bus charge only when needed. Chargers can be programmed to function at times of day when energy demand is lowest and power is less expensive.

Manufacturers are introducing buses equipped with bidirectional charging capability that can send stored electricity back to the grid when they are not in service. During summer months, when many school buses are not in use and power usage often peaks, utilities soon may be able to call on school districts to make charged buses available to help ease demand load. These buses can also be used as mobile generators during power outages and emergencies.

In a 2022 study, researchers at the University of North Carolina analyzed how the state’s utilities could use school buses with vehicle-to-grid charging to manage peak power demand while taking the buses’ schedules into account. They estimated that a fleet of 14,000 buses could provide about 2.6 gigawatt-hours of electricity to the grid on an average winter weekend day in North Carolina, reducing utilities’ dependence on natural gas and avoiding up to 1,130 tons of carbon dioxide emissions per day.

Cleaner air is likely to pay off in improved student performance. In a 2019 study, researchers found that retrofitting 2,656 diesel buses in Georgia – adding new components to reduce the buses’ emissions – was associated with positive effects on students’ respiratory health, and that districts with retrofitted diesel buses experienced test score gains in English and math. Since even modernized diesel vehicles still generate air pollutants, shifting to electric buses would likely produce even larger increases.

Spreading the benefits

Federal and state agencies are moving to speed up the transition to electric school buses. The American Rescue Plan, enacted in 2021 to provide economic relief during the COVID-19 pandemic, included $7 million in rebates for school districts in underserved communities, Tribal schools and private fleets serving schools that purchase electric buses.

In March 2022 the Environmental Protection Agency awarded funding for 23 electric school bus replacement programs and associated charging infrastructure in 11 states. And New York state’s fiscal 2023 budget includes a nation-leading requirement that all new school bus purchases must be electric starting in July 2027, and that all school buses in service must be zero-emission by 2035. The budget allocates $500 million in potential state funding for school bus electrification as part of a larger environmental bond act, which will be on the ballot in November 2022.

Riding the iconic yellow school bus is a formative experience for millions of kids across the U.S. If more districts make the shift away from diesel, I believe it will become a greener and healthier trip and a step toward the zero-emissions future our nation’s children deserve.