Electric buses used for public transit are often charged in two ways: depot charging and on-route charging. On-route charging can allow for continuous charging of transit vehicles throughout the day but typically requires fast-charging infrastructure (Level 3 Charging) that requires high power.
Applicability, Benefits, and Tradeoffs
On-route charging allows electric buses to operate longer on the road by removing the need to return to a depot for extended times to charge. This may be ideal for routes that need to operate frequently, or buses that drive more miles, and cannot have long interruptions for charging. Another consideration is that on-route charging is generally done at higher power rates (up to 500kW), which is faster, but can lead to expensive utility demand charges and thus higher operating costs. The table below lists common benefits and tradeoffs of EVs and indicates how well this use case achieves these benefits. Green indicates the use case typically achieves the benefit. Yellow indicates the use case sometimes achieves the benefit. Red indicates the use case does not achieve the benefit.
Reduced Traffic Congestion: Public transit buses reduce traffic congestion by providing transportation for multiple community members with one vehicle, rather than if community members each drove personal vehicles.
Increased Equity and Accessibility: Investing in public transit can help remove economic and accessibility barriers to transportation for low-income households, seniors, those with disabilities, students, and other disadvantaged groups that may not have access to reliable personal vehicles. From an equity standpoint, electric busses also ensure that riders and those in proximity are not exposed to the harmful tailpipe emissions from diesel buses. These pollutants have health and environmental impacts that disproportionately affect sensitive populations such as children, pregnant women, seniors, and those with respiratory illnesses or cardiac conditions.
Reduced Emissions: Public transit buses offer significant opportunities for electrification. More than 340 electric buses are currently operating in the United States, with another 1,200 electric transit buses on order. Electrifying transportation creates the opportunity to energize transport with renewable energy, reducing overall emissions from the transportation sector. When community members use public transit, rather than personal vehicles, that can also reduce to total vehicle miles traveled in the community, which can result in significant reductions in pollutants. One study in the Northeast and Mid-Atlantic regions demonstrated that electrifying heavy duty diesel vehicles, such as transit buses, resulted in 33 times greater reduction in nitrogen oxide and 7.5 times greater reduction in particulate matter per mile than electrifying gasoline powered light duty vehicles.
User Economic Benefits: The economic benefits for passengers often depend on the fare charged to public transit passengers and how this fare compares to the income of the community members. In Missoula, the local transportation system does not charge a fare to passengers, ensuring that all community members have access to consistent, reliable transport regardless of their income. Using public transportation, even when a fare is charged, is often less expensive than purchasing, operating, and maintaining a personal vehicle.
Owner Economic Benefits: To help reduce economic costs due to utility demand charges associated with on-route charging, transit agencies can consider deploying several electric buses. Cost-benefit analysis on transit bus charging for potential electric transit buses in Bozeman concluded that Bozeman would need to deploy at least six electric buses to replace six diesel buses in their current fleet using existing routes to mitigate the demand charges from on-route bus charging. This is because the costs are spread across the operating budgets of multiple buses.
Renewable Energy Co-Location: On-route charging uses fast-charging infrastructure, which demands a large amount of power. If the bus is on-route during the day, it may still prove challenging for a solar array to provide sufficient power, even if the array is very large. Pairing the solar PV array with energy storage can help overcome these issues.