Zero-emission technology: next-generation bus fleets


What will the electric-driven landscape look like in 10 years? With leaders from some of North America leading manufacturers, we explore the advancements, regulations and issues surrounding zero-emission technology.

Tom Webbdirector, business developmentBAE Systems

Macy Neshatisenior vice presidentBYD Heavy Industries

Oscar Pardinasregional sales managerENC

David Warrendirector of sustainable transportationNew Flyer

Mike Finnerndirector, customer serviceProterra

Philipp Looserhead of business unit commercial vehicle
technology, North America
ZF North America

What are the most significant advancements in electric vehicles in the past few years?

Tom Webb: Range, price and competition are the big developments that have occurred in the last few years.  Bus range has increased from below 100 miles per charge a few years back, to over 200 miles per charge today due to improvements in battery technology, packaging and drive-line efficiency. Price has also come down from about $1 million per bus to about $850,000 per bus, largely due to growth in battery production output and increased competition.  Hydrogen fuel cell electric buses are demonstrating longer life of the fuel cell stack (or engine) and costs have also come down.  Fleet customers have more suppliers and electric products to choose from today than they had five years ago.

Macy Neshati: The most significant improvement is in the energy density of the batteries, meaning the same battery weight and size is able to store and provide significantly more energy.  This has allowed BYD to deliver buses with up to 275 miles of range on a single charge.

Oscar Pardinas: The most significant advancements have come in the way of battery chemistry, technology, development and packaging. Batteries are the key to BEB success. Batteries continue to increase in energy density, providing more range, they are physically getting smaller and lighter, allowing for more batteries, and their cost is coming down. The same goes for hydrogen technology. Fuel cells are getting smaller, more powerful and lower in cost.

David Warren: Buses equipped with electric motors and powered by overhead wires were first introduced over 100 years ago. The emergence of the battery-electric bus directly correlates to advancements in Lithium-Ion technology led by portable consumer products; now it is the dominant battery technology used in electric vehicles of all types. Ongoing research and development has yielded significantly higher energy density (amount of energy stored per pound) and cost reductions, which has become the catalyst for sustained commercial growth. As an example, when New Flyer introduced the Xcelsior battery-electric bus in 2014, battery capacity was limited to 300 kWh. Three and half years later, the same Xcelsior can be equipped with up to 480 kWh of batteries, a remarkable 60 percent improvement in range capability.

Mike Finnern: There have been many significant advancements in heavy-duty electric vehicles (EVs) in the last few years.  From a technology standpoint, the development of incredibly high energy-density batteries built specifically for the HD transit market that allow all-day operation on a single charge may be the most important as it allows nearly any transit route to be electrified.  A second major advancement is the development of advanced, integrated diagnostic tools enabling quick and reliable performance monitoring and troubleshooting. 

Just as important as technology advances are the developments in industry knowledge and commitment.  Simply put, agencies such as APTA, EPRI, utility commissions, industry groups and of course transit agencies are rapidly improving their understanding of EV’s and working to solve the deployment equation for their particular system.

What are the most significant advancements in electric componentry in the past few years?

Philipp Looser: Fully-developed electric propulsion components are being integrated into new buses such as central drive motors, as well as electric wheel ends.  ZF can provide both solutions with the CeTrax combined drive motor and integrated planetary reduction and the AVE 130 portal electric drive axle.

Lighter, higher-density energy storage systems are making their way into the market. Electrified accessories, which are more efficient than mechanically driven components are used in power steering, AC compressors and other bus systems.

Then there is the world of connectivity which can provide fleet management apps as well as real time diagnostics and vehicle tracking.     

Please distinguish the different types of zero-emission
drive systems.

Looser: The market is focused on three types of zero emission including inductive / conductive power transmission, battery electric and what many consider to be the real future, the hydrogen fuel cell.

Typically, the propulsion components do not care by which means they receive power, as is the case with the ZF CeTrax as well as the AVE 130.    

For which applications are electric vehicles best suited? How are you working to expand into other applications?

Webb: The market is offering electric vehicles for almost every bus application today including paratransit, coach and articulated buses.  However not all products are well-suited to every application, drive cycle and climate.  In general, battery-electric solutions are best-suited to mild climates with favorable duty cycles (i.e. short range, peak trip and relatively flat terrain).  Battery-electric buses require supplemental heat to operate in cold climates and very large batteries (e.g. 500kWhr or more) or in route opportunity charging to operate all day.  BAE Systems offers both overnight depot and in route opportunity charge options.  We also offer hydrogen electric propulsion that can generally handle long-range routes, hills and cold temperatures. We are actively working to qualify and bring to market better battery and hydrogen solutions to handle the wide demands found in public transit. 

Neshati: While we would argue that all vehicle applications are best-suited for electrification, BYD believes the most sensible conditions are those with: (1) a defined duty cycle so the vehicles can be designed accordingly with limited waste; (2) frequent starts and stops as electric vehicles have regenerative braking and will therefore be much more efficient in these conditions; and (3) high idle times as electric vehicles do not have any waste during these times, whereas internal combustion engines do. 

Beyond buses, we find these conditions are met in many heavy-duty trucking applications, such as goods delivery, port operations, and refuse removal. BYD produces trucks designed for these uses.

Pardinas: In transit, the biggest concern is range. The application of electric propulsion buses is directly related to the route profile. There are several profiles that come up for a BEB:

• A circulator. This is a route that circles around the same route. The route is well within the range of the batteries. The route has a dwell point where the driver stops every cycle. At this point, an opportunity (on route) charger can be used to recharge the batteries and run all day without returning to the yard.

• A deadhead or “tripper” route. This route has a one-way or round-trip distance that is consistent with battery capability. Depending on distance constraints, the bus could be charged overnight at the depot perform the route and then come back to the yard or remote charging location for a recharge and operate the afternoon rush.

• A route within the range of the batteries. This is the most obvious and desired choice. Here the route matches up with the range of the bus and the vehicle can perform all day without the need for a recharge.

The great advantage of a hydrogen fuel cell bus is that most of these types of services can be met today using hydrogen fuel cell buses.

Warren: Range remains the greatest challenge for a battery electric bus in today’s market. As a matter of science, lithium-ion batteries remain significantly heavier than the amount of energy that can be stored in CNG or diesel. In a worst-case operating environment, the constraints on the electric bus design have limits on the range without re-charging to ensure full passenger loading (seated and standees). Electric buses are best-suited for routes which are either: A) Service blocks that are less than 175 miles, B) Conducive to on-route high-power recharging throughout the day, or C) For buses that have that the ability to return to the depot to recharge up to 2-3 hours during the day.

Finnern: Any vehicle currently powered by fossil fuels is ripe for EV conversion. Proterra continues to push forward in developing battery technology for use in heavy-duty vehicles.  While we have been focused exclusively on the bus fleet market, specifically public transit and adjacent commercial operations, such as airports, universities and corporate shuttles, we believe that our technology has application in the broader heavy-duty vehicle market.

Why is a modular approach important to an electric drive system?

Looser: Modular componentry provides the OEM with flexibility to integrate in ways that are best and easiest for their bus chassis. Weight distribution can be optimized and maintenance of the components can be considered in the installation design.

Modular systems also can allow for commonality between vehicle types for example using the ZF AVE 130 as the drive axle in a 40-foot bus and in an articulated bus either as the center axle (puller) or rear axle (pusher).

How are zero-emission vehicles affecting ridership for the agencies purchasing them?

Webb: Zero-emission vehicles have strong appeal to riders, the public and politicians because they are perceived to be clean, quiet, and sustainable.  It has yet to be shown whether zero-emission vehicles will boost ridership, but many agencies investing in electric buses are betting that ridership will grow. Today, some battery-electric buses may limit passenger-carrying capacity if they carry too much battery weight.  This trade-off will improve in time as battery energy density improves.  Hydrogen fuel cell electric buses do not limit passenger- carrying capacity.

Neshati: Electric buses are having a positive impact on ridership.  Riders often tell BYD’s transit agency customers how they appreciate the fact that our buses are virtually silent, that the ride is smooth, and that they appreciate the fact that they are fully zero-emission. Customers tell us that riders report passing on a diesel bus to wait for an electric one!

Pardinas: Agencies that have bought electric vehicles have undertaken major advertising campaigns targeted at ridership. They tend to be self-promotion for their clean efforts. Some positive feedback that agencies have received from BEB riders is: the environmental, “green” factor; electric buses are quiet so you can carry a conversation easier; and the buses do not have the diesel/fuel smell.

Warren: New Flyer is extremely pleased with ridership response to our recent electric bus deliveries in several major cities, including Chicago, Washington DC, Seattle and San Francisco. Transit riders praise the Xcelsior’s highly stylized, comfortable and quiet design. From urban residents to commuters, riders are sharing their positive experiences with New Flyer electric buses using social media and active participation in transit planning. Rider response has directly resulted in re-orders of New Flyer zero-emissions buses to meet growing service needs. Outside of major cities, New Flyer is involved with the deployment of electric buses in rural and disadvantaged communities, where riders rely on transit service and the associated clean-air benefits.

Finnern: Transit agencies have done significant public outreach to raise awareness of zero-emission vehicles. Cases in point, two Proterra customers have devoted substantial resources to educate their communities about the benefits of zero-emission battery-electric transit buses. Complementary to this, has been extensive work done by the National Renewable Energy Laboratory, American Lung Association, the Sierra Club and the Union of Concerned Scientists. This work has paid off with momentum surrounding the public’s support for agencies’ effort to convert fleets to 100 percent electric.  For example, when agencies host public hearings to consider EV transit, the public resoundingly offers a positive, “yes.”  Plus, over the past year, it’s easy to point to successfully passed ballot initiatives that have included clean transportation elements — demonstrating again that the public is on board with zero-emission transit.  And, anecdotally, drivers and riders, particularly those with respiratory health issues and with children and aging parents, have expressed their preference for battery-electric vehicles over fossil fuel buses.

Does the position of an electric drive system affect performance? If so, how?

Looser: The position of the drive system affects the efficiency depending on the position of the electric motor. The fewer teeth engaged between the motor and wheel, the less power loss and noise emission. Design and manufacturing of gears is still a key competence of electric drive system suppliers which influences the efficiency of a system considerably. Furthermore, the position of the drive system can impact the ride quality since it affects the center of gravity of the vehicle. In the axle, integrated electric motors support lightweight designs, low center of gravity and more available space for passengers or other components.

What’s the most important piece of advice you’d give to an agency looking to incorporate (or transition to) all-electric vehicles into a 100-percent diesel-fueled fleet?

Webb: Do your homework, assume change, and build lasting partnerships.  It is vitally important that agencies educate themselves on the technology, market, performance, costs and duty cycle suitability.  They need to take the time to study, evaluate and deliberate before commencing down the electric pathway.  The benefits are there but only if they manage the transition wisely.  They should assume more change and disruption will occur in both technology (better batteries) and industry (new entrants).  Finally take the time to build partnerships with internal departments and external fuel, infrastructure and technology partners.  You need each other to be successful for the long term.   

Neshati: You won’t regret it! BYD customers are transitioning to electric buses for a host of reasons and many are surprised by the benefits that they didn’t expect.  Most are transitioning due to the reduced emissions, but they’re happily surprised that the fuel and maintenance savings provide a lower overall total cost of ownership, that their drivers enjoy learning and driving the very latest technology, and that riders are excited about the buses.

Pardinas: Plan, plan and plan again. Everything changes when you transition from diesel or CNG to electric. First is the cost of the equipment. You can consider a nearly 2-to-1 cost factor as electric buses are in the $800,000 range. Then there is infrastructure. How much power do you have available at your depot? In a small (5 bus) operation, charging 5 x 400Kw buses, it is not such a big deal – 2 Mega Watts of energy. When you are talking about 100 buses, that number becomes 40000Kw or 40 Mega Watts, which will almost always require the addition of a power installation just to charge the buses. Charging management technology as well as peak power avoidance become a concern. For those opting for HFC buses, there is the availability of hydrogen and the cost of the fueling infrastructure. You will also need to determine how to park your buses in the yard to accommodate charging, as well as consider fueling methods, in addition to mechanics – less diesel and more electricians, and their ability to service a new platform. You’ll also need to teach drivers how to drive all over again to maximize battery life and regenerative charging. All are part of the BEB operation.

Warren: Due to infrastructure required to operate and maintain battery electric fleets, total fleet replacement with battery-electric is not feasible today for most urban, metropolitan, and municipal cities. A blended approach utilizing multiple propulsions is ideal.

Deploying electric buses beyond a pilot fleet of 15-25 buses requires a phased approach to manage operational risks, allow for technology advancements to solve range limitations, and permit agencies to incorporate learned best practices from transit peers. For this reason, the transition to a zero-emission transit fleet will be an evolution, rather than a revolution. New Flyer’s Xcelsior platform, shared between all six types of available propulsion systems, supports a controlled migration to an eFleet by leveraging commonality for training and maintenance, while circumventing chaos with unique equipment and special processes.

Finnern: If you are interested in moving away from fossil fuels, the best advice is to spend the time now to develop a long-term plan that considers full electrification.  Overall project success and costs can be greatly reduced if you can plan now for a full-electric fleet, even if you intend to only start with a small deployment. 

What will the electric-driven transit landscape ‘look’ like in five years? 10 years?

Webb: There will be more electric buses operating in our cities, but we will still have a blend of offerings on the road from full-electric buses, electric accessories on conventional-powertrains, and hybrid-electric powertrains. Battery technology will continue to improve over time and corresponding costs will continue to come down. There will be new and improved charging schemes and better protocols and standards.  New companies and technology suppliers will enter the market, competition will increase, and we may see some consolidation as well. 

Neshati: Within five to 10 years, BYD foresees all new purchases of transit vehicles will be all-electric.  There are a number of established companies that offer electric buses at a price that isn’t much higher than conventional buses, and within 5-10 years we expect price parity.  Taking into account savings on fuel and maintenance, the cost of electric buses will then be significantly lower than conventional buses. At that point, there should be no reason not to transition to an electric fleet.

Pardinas: Five years may be too short to make a big impact. Batteries are increasing in energy density at an estimated industry rate of 5 percent per year and decreasing in costs at about the same rate. If we consider an industry transit route standard of 350 miles per day and an average requirement of 2Kw / mile, a true equal to a diesel bus would need 700Kw + another 10 percent reserve, of battery storage. Today, 700Kw at the weight of current battery packs would consume the majority of the GVWR of the bus. Batteries need to be lighter and increase in energy density in order to achieve this.  Perhaps a leapfrog technology in the battery space can accomplish the task.

It is also possible that manufacturing technologies like composites or other hybrid construction will help lighten the weight of these vehicles and increase efficiency.

In 10 years, I think that the mainstream auto industry will have driven the technology forward to the point that it is cheaper to design manufacture and operate electric vehicles than fossil fuels. Solar technology is also advancing and the idea of having free “energy storage” off of the grid, will reduce operation costs significantly.

Warren: It is difficult to accurately predict what the electric-driven landscape will look like, however, it is a safe bet to say the introduction of battery-electric buses to bus fleets will become increasingly prevalent during this timeframe. It is also anticipated that research, development, and innovation over the coming five and 10 years will see further sophistication in battery and electric propulsion. While savings are conditional on a number of factors, including temperature, passenger loads, topography, weight of bus, driver habits, and HVAC usage, on average a battery-electric Xcelsior bus can provide up to $400,000 in fuel savings and up to $125,000 in maintenance savings per bus over a 12-year life span.

Finnern: Over the next five years, there will be a tremendous push to convert existing fossil fuel-burning fleets to zero-emission vehicles.  Already, agencies and municipalities across the U.S. have made a commitment to cleaner, quieter, healthier transit.  These include:



Antelope Valley Transit Authority


San Joaquin Regional Transit District


Foothill Transit


Los Angeles Department of Transportation



The City of Portland is committed to 100 percent renewables, including in transportation



Seneca is the first community in the U.S. with an all-electric fleet



The City of Park City pledges to be carbon neutral by 2032



King County Metro

With this domino effect happening at such a swift pace, it’s our belief that the time will come, in the next 10 years, where no U.S. transit agency will be purchasing a diesel bus.

And what about electric componentry in the next five to 10 years?

Looser: The electric drive components will not change much other than gains in efficiency and power-to-weight ratio.  Of course, batteries will continue to gain higher energy density.

We expect that charging systems will also develop further and more charging stations will become available.

There will be many improvements in the longer term, of course driven by market demand and competition between suppliers.  Recent announcements by cities and large transit authorities to have zero- emission fleets within the next 10 to 20 years proves the direction the market is headed and the technology will be driven. 

Energy storage in terms of higher developed battery technology will have to be realized as not only buses, but other commercial vehicles- not to mention automobiles becoming electrified.  And, of course, there is high expectation for the hydrogen fuel cell to be used more extensively within the next 10 years.