Plug-in and Ride: The Promise and Potential Challenges of Electric Buses

By Tracy Zafian, UMTC Research Fellow

The use of electric buses and other zero emission vehicles (ZEVs) holds great promise to help reduce vehicle emissions and promote a clearer, less polluting transportation sector.

Transit bus systems offer a great venue for deploying and testing the latest ZEV technologies. An estimated 40 U.S. transit systems now include electric-power buses as part of their fleet. To date, bus systems in California have been the greatest adopters of electric buses. The Santa Barbara Metropolitan Transit District began using electric buses in 2003 and currently has 14 in operation. Stanford University Transit presently has a fleet of 23 electric buses, which it launched in 2014. Foothill Transit in Northern California started using electric buses in 2010 and now has 30 in use. Foothill Transit has pledged to change all its buses over to electric power by 2030. Foothill Transit estimates that already, its annual electric buses eliminate the same amount of emissions as 2,424 gasoline-powered cars. A number of other California transit agencies have smaller fleets of electric buses.

Two UMTC Research Affiliates recently developed a comprehensive review of past and current electric bus deployments nationally. This research was led by Professor Eleni Christofa in Civil and Environmental Engineering and Professor Krystal Pollitt in Environmental Health Sciences. The review included discussions of the three main types of electric-power buses currently in use, and of different facets and impacts of transit agencies’ change to electric buses, including areas of challenge.

The primary type of electric bus in use today is the battery electric (BE) bus, and more than 20 U.S. transit agencies have incorporated BE buses into their operations, including the Worcester Regional Transit Authority (WRTA) and the Pioneer Valley Transit Authority (PVTA). BE buses contain an onboard electric battery, which provides all their power. These batteries are typically re-charged through plug-in stations; BE buses also capture and then use energy from regenerative braking. BE buses have no direct vehicle emissions, but there may be atmospheric pollutants associated with the generation of electricity used for charging their onboard batteries. One potential challenge with BE buses is the short driving range (30 to 130 miles) before needing to be recharged, and the impact of the need for recharging on route scheduling. These buses will typically be recharged at bus stop charging stations during their routes for quick charges (5 to 15 minutes). Some transit agencies also utilize slower charging stations at a central location such as a bus garage, for when BE buses are out of service. Even with the quick charges, it is important that bus schedules be adjusted to reflect the charging time.

BE buses are more expensive to purchase than traditional diesel-engine buses ($750,000 per bus compared to $435,000 per bus, respectively); however, they have a longer expected lifespan than diesel buses. BE buses also save fuel and maintenance costs. Proterra has stated that overall, the lifecycle costs of BE and diesel buses are similar. The PVTA estimates that each of its BE buses will save the agency $448,000 combined in fuel and maintenance costs. The PVTA also calculated that each of its BE buses will eliminate 244,000 pounds of carbon dioxide emissions compared to their diesel bus counterparts.

The second main type of zero-emissions buses are those powered by hydrogen fuel cell batteries. Fuel cell battery electric (FCBE) buses store hydrogen onboard in storage tanks and the hydrogen is then supplied to the fuel cells to generate electricity to power the vehicles. There are no emissions, as water is the only by-product for FCBEs. There are presently seven U.S. transit agencies operating FCBE buses; the electric bus at the Massachusetts Bay Transportation Authority (MBTA) uses FCBE technology.

With a typical purchase price of $1.2 million, an FCBE bus is much more expensive to purchase than a conventional diesel bus ($435,000) or a compressed natural gas bus ($500,000). FCBE buses also require special training for bus operators on using the technology and special hydrogen storing and fueling facilities; these are typically located at bus depots to allow vehicles to be refueled at day’s end. On the plus side, the fuel economy for FCBE buses has been reported to be double that for compressed natural gas or diesel buses.

The third main type of zero emission buses are fuel cell hybrid (FCH) plug-in buses which use a combination of both onboard batteries and hydrogen fuel cells. To date, only 7 U.S. transit agencies have used FCH buses, mainly in short-term demonstration projects. Transit agencies that have tried FCH buses have consistently reported significant downtime for the buses, due to issues with the batteries, the fuel cell systems, and the hybrid integrator, and to challenges in diagnosing specific problems.

Currently, BE buses seem to hold the most promise for wider deployment and use.



Bridgewater State University becomes a “LivingLab”

By Uma Shama and Lawrence Harman, Bridgewater State University

This summer, Bridgewater State University (BSU) has become a “LivingLab” with the BSU GeoGraphics Lab using campus parking lots to research Small Unmanned Aircraft System Remote Sensing Platforms for transportation.

Lab co-directors and UMTC Research Affiliates Dr. Uma Shama and Mr. Lawrence Harman are using aircraft systems produced by the company DJI to develop image archives of near-empty parking lots on campus with the research goal of using those archives as a baseline for analysis of BSU’s smart parking initiatives.  The aircraft systems (sUAS and software) are low-cost, but they are still able to create high-resolution 2D and 3D web mapping data that emphasizes transportation flows within the LivingLab area.

The research is also working to create Imagery Collection Techniques that comply with the flight rules established in 2016 by the Federal Aviation Administration.  These rules include restrictions on operating unmanned aircraft over people or private property.

Potential applications of the research outside of Bridgewater State, include real-time monitoring and time-series analysis for evaluating mobility investments made by MassDOT, municipalities, and the Massachusetts Bay Transportation Authority.

Partnerships have been a key part of the project’s success.  Collaboration between the BSU Facilities Management and Planning Department, the BSU Police Department, the BSU Aviation Science Department, and the Veterans and Military Affairs Office have been established.  Partnerships have also extended to regional planning and regional transit agencies.

This “LivingLab” initiative builds on a decade of remote sensing research that seeks to apply spatial information technologies to mobility management issues and will help to improve public services locally, regionally, and globally.