Paving the Road for Zero-Emission Bus Fleets

This summer, the U.S. Department of Transportation's Federal Transit Administration (FTA) awarded $1.66 billion in grants, funded by the Infrastructure Investment and Jobs Act (IIJA), for the purchase more than 1,800 new buses, most of them zero emission. This investment in 150 bus fleets and facilities nationwide helps meet the U.S. government’s goal of net-zero emissions by 2050.

As part of the global mission to address climate change, the transportation sector has emerged as a key lynchpin in reducing greenhouse emissions. The federal Environmental Protection Agency (EPA) has identified the nation’s transportation network as the single largest source of greenhouse emissions in the United States. The California Air Resources Board (CARB) mandated the transition to 100 percent zero-emission bus fleets by 2040. The private sector is helping agencies facilitate this transition to achieve their zero emissions goals.

The Los Angeles Country Metropolitan Transportation Authority (L.A. Metro), which oversees the third largest bus fleet in North America, has initiated one of the most significant efforts to date. L.A. Metro plans to transition its entire bus fleet and bus maintenance facilities from compressed natural gas to zero-emission technology. STV, in joint venture ZEBGO Partners, is providing a range of services to help L.A. Metro achieve these goals, including:

• Assisting in the development of a Zero Emissions Master Plan.
• Evaluating existing infrastructure for integration needs and the recommended placement for in-route bus chargers.
• Analyzing bus route and schedule.
• Analyzing life-cycle cost for all emerging relevant technologies.
• Investigating potential funding opportunities to support this plan.

A similar effort was performed in San Diego with the North County Transit District (NCTD) to provide planning support for a phased implementation to transition from diesel and compressed natural gas buses to battery electric and hydrogen fuel cell vehicles. The implementation includes modifications to NCTD’s facilities, as well as revising the existing bus site layouts and siting potential in-route charging stations across various NCTD bus routes.

Tools of the Trade

New tools are helping agencies with zero-emission and climate change goals to identify potential technologies to advance environmentally friendly improvements to existing bus infrastructure. One of the biggest challenges transit operators may face in the transition to zero-emission buses is aligning achievable vehicle range with the daily sequence of routes that each bus is scheduled to run, what the industry calls a “block.” To address this challenge, STV developed a tool that enables project teams to study bus route operating factors in a dynamic model. The Performance Evaluation of Electric bus Routes (PEER) tool incorporates the topography of the routes, stops, passenger counts and schedules, along with everything physically impacting what a bus does on a given route.

Transit agencies launching zero-emission initiatives want to know how many buses they can replace immediately without impacting the current schedule. For those that can’t be replaced on a one-to-one ratio with battery electric buses (BEBs) currently available in the market, they want to know how many new buses they will need. In the wake of the pandemic, fulfillment of fleet replacement procurements from bus manufacturers can take time and agencies need accurate knowledge about acquisition lead times.

For a block, STV’s PEER model derives projected kilowatt-hour per mile, expected total energy usage and state of charge status while in operation to generate data needed to determine how much of the current schedule is completable with today’s zero emission bus technology. PEER also determines total energy load required to support each phase of the transition toward a 100 percent zero-emissions bus fleet.

Agencies can also work with the private sector with the development of a fleet replacement plan that defines the agency’s conversion to a zero-emission bus fleet over time, following FTA guidelines and accounting for the rate that emerging technology migrates to commercially viable over time.

Sustainable Batteries of the Future

The other moving target that transit operators need to account for to get to zero emissions is adapting to the fact that the green technology is constantly changing and improving.

Agencies should consider analyzing existing routes, traffic conditions, climate, topographical conditions, ridership and energy consumption to determine how existing routes can take advantage of this constantly changing environment, while also evaluating the impact of bus charging interfaces such as plug-in, pantograph and inductive.

Agencies have come to prioritize integrating BEBs into service because these vehicles provide lower operating and maintenance costs, while also meeting the federal, state and local requirements for zero emissions and sustainability.

In 2018, 300 BEBs were used throughout the country. But the FTA’s Low- or No-Emissions Grant program (or Lo-No) recently awarded funding to 52 projects across 41 states that will greatly expand that number. Additionally, continuous advancements in battery technology are expected to introduce more cost-effective choices for operators. The industry could see at least a five percent increase in batteries’ energy density each year for the next decade. For each project, develop a charging infrastructure design and electrical load analysis for a bus facility based on these projected improvements in battery storage energy densities.

When developing a master fleet zero-emission implementation plan, agencies should account for “forward and backward compatibility” – using charging stations that are compatible with older technology, current standards and the more compact and efficient models expected in the future.

Advancements in Fuel Cell Technology

Fuel Cell Electric Buses (FCEB) are another zero-emissions solution that transit agencies across the United States are implementing. Hyundai and Toyota have both initiated construction of fuel cell production facilities here in the United States. This provides a more robust local supply chain and increasingly competitive pricing.

Fuel cell buses continue to advance in design with the latest configurations being the battery dominant fuel cell bus, where the fuel cell is sized to recharge batteries on board the bus. This approach is often compared to talking on a mobile phone with the charger connected: the batteries do not die as quickly, since the battery is being recharged as the phone is used. The same happens with the battery dominant fuel cell bus design, giving the bus greater range than BEBs. Some FCEBs are now capable of achieving more than 300 miles in daily operating range.

Powering the Future: Micro-Grids and Resilience

With the expansion of solar, wind and energy storage options, the adoption of microgrid technology to support BEB deployments is becoming more viable. Energy sources available to integrate into an on-site power generation/emergency backup microgrid include solar photovoltaic, wind turbines, on-site battery storage, fuel cells, conventional turbines, micro-turbines and geo-thermal energy sources. Integration of on-site generated power not only offers the local bus agency the potential for reduced operating costs and improved resilience, but it also can have significant effects (both positive and negative) on the local utility electrical providers’ service and rates and the ability of transit providers to continue using their buses as emergency support vehicles.

In order to determine the benefit of the installation of a microgrid, either connected to a grid or autonomous, a number of key factors require evaluation. A primary objective is to identify the operational risk factors transit agencies may face and what mitigation measure might be able to address service interruption risks, so bus operations and infrastructure modifications will be more resilient to disruption from outside events. Another objective is to provide supplemental power during high-demand periods, such as extreme weather, when interconnected with the grid. These power-generating and storing technologies are used to reduce the demand from the grid so that the transit agency can avoid demand charges or time-of-use charges that may be imposed by their grid power utility. Demand charges are an increased cost for energy assessed on the transit agency when the transit agency demands higher energy levels to charge buses at peak load times for durations as short as 15 minutes. They can be very costly and make a big impact on fuel costs for the agency. By using an alternative power supply such as those listed here, the agency can reduce its short-term demand on the utility by deploying these various micro-grid technologies.

Affecting Change at a Higher Level

Beyond project work, an important way to make a positive impact is through industry stewardship. We both currently serve as industry advisors to the Society of Automotive Engineers (SAE), a globally active association that since 1904, has been responsible for developing standards and best practices. SAE has proven to be instrumental in cases for the U.S. National Highway Traffic Safety Administration and its recommendations.

Last year, the organization developed a universal charging standard for overhead pantograph charging that established a common vehicle interface design. SAE set the standard for this vehicle interface so that operators aren’t beholden to a single manufacturer or require adapters to charge their fleets.

The work being done now in California will continue to spread to other parts of the United States. And as the nation continues to integrate zero-emissions technologies, organizations like SAE are already looking ahead. SAE may next look to set a standard for high power inductive (wireless) charging.

Michael E. Broe is a senior engineering operations manager at STV with more than 40 years of experience in vehicle operations and maintenance. He previously worked for New York City Transit (NYCT) Department of Buses as deputy general manager of the Manhattan Division and general manager of the Brooklyn Division, and worked as Boston’s operations manager for Greyhound Bus Lines. He is a major contributor to the PEER modeling program.

David W. Casper, P.E., is a senior vehicle engineer and program manager at STVwith experience directing activities related to the design, manufacturing and introduction of more than 2,000 vehicles into service. He has expertise in bus vehicle technology and the planning and procurement of energy-efficient and environmentally responsible buses, including clean diesel, hybrid, zero emission trolley bus and ZEB fleets. His background also includes extensive overhaul/modernization programs for commuter rail, rapid transit and light rail vehicles. He is also one of the developers of the PEER modelling program.