When acquiring zero-emission buses, think systemwide

The RTD’s holistic approach to battery electric buses

By  Henry Stopplecamp, Assistant General Manager, Capital Programs | Regional Transportation District

With the federal government committed to funding zero-emission buses and many jurisdictions setting ambitious air quality initiatives, transitioning to zero-emission buses has become a priority for transit agencies across the country, Denver’s Regional Transportation District included.

The RTD operates and maintains a fleet of more than 1,000 diesel buses that serve 24,000 square miles of the metro area. We also own a subfleet of 36 battery electric buses that we have been operating on Denver’s 16th Street Mall for several years. Next year, we will expand our fleet with 17 new 40-foot Xcelsior CHARGE NG™ heavy-duty battery electric transit buses. The new technology will advance us toward goals outlined in the Colorado Climate Action Plan and Colorado’s Electric Vehicles Plan, which requires transit fleets to transition to 100% zero-emission vehicles by 2050.

When procuring BEBs, the tendency is to focus on the brand-new buses and their benefits. But the real focus should be on the system – how the new buses will affect routes, operations, power supply and infrastructure. While the newer, long-range, heavy-load battery-powered buses offer a quieter ride, cleaner air, longer range and reduced operational and maintenance costs, their integration will impact the entire system. We are performing a systemwide assessment to best plan for this new technology.

Readying our facilities

Integrating the new technology into the RTD’s 30- and 40-year-old bus facilities is perhaps the most challenging aspect of transitioning to BEBs. Because of Denver’s frigid winter climate, on-route charging isn’t an option, which means our garages need to be reconfigured to allow space for transformers, switchgear, power cabinets and dispensers. We also are looking at replacing lifts and beefing up our inspection pits to accommodate the new vehicles, which are heavier than standard over-the-road coaches.

We are confronted with the challenge of making these modifications without the guidance of building codes for zero-emission vehicles. Undoubtedly, as alternatively powered vehicles become mainstream, those codes will emerge, but for now, we are soliciting the insights of city, state and federal regulators and first responders to define a set of safety protocols and standards.

Parking our new fleet

Our garages house 120 to 220 diesel buses, parked nose to tail with approximately 4 feet between each bus. Housing the new BEBs in the same depot as our diesel buses presents a considerable risk. Thermal runaways, where the bus’s battery system overheats and starts a fire, are more prominent on the newer, long-range, heavy-load batteries. If one BEB overheats and catches fire and all of the BEBs are parked nose to tail like our diesel fleet, we could have a domino effect of bus after bus ablaze. The worst-case scenario is the RTD loses all 220 buses in that garage and has to cut service to the community until we can replace those buses. That risk – combined with the need and expense to retrofit existing garages to accommodate the new BEBs – is why the RTD is considering a stand-alone facility for this and future procurements.

Connecting to the power supply

Charging 17 buses requires a massive amount of energy. Having a BEB facility located at the end of the power supply after other utility customers have pulled down the energy they need is undesirable. If a blackout occurs, as it did with our 16th Street Mall buses, we may walk in the next morning to a fleet only half-charged, illustrating the need for an ample supply of electricity and a backup power source in case of an outage.

Needless to say, engaging the local power company early as a partner in our transition to zero emissions is essential. The supplier needs to know how much power our new BEBs will require and when we need it. And, we need to know they can supply it. We are currently collaborating with the utility company to determine the answers to these questions as well as others, such as the best time of day to charge our buses, demand fees and how they will impact the cost of charging our BEBs.

Rethinking blocks and routes

Our diesel bus blocks range from 400 to 600 miles, but we will not get that range from the new BEBs. Because their battery range is 200 miles on a single charge, we will most likely bring them into the depot mid-day to recharge and then send them back out in the afternoon. That one change to operations requires us to rethink our routes and blocks to maximize battery range and minimize deadhead.

Involving the community

It also requires the BEBs to be stored, charged and maintained in the communities they serve. Moving forward, the RTD plans to solicit significant involvement from the local communities and municipalities to determine the permitting requirements for a new garage. From there, we will work to mitigate concerns by exceeding the requirements for aesthetics, vibration and light pollution. There won’t be a major impact to the community if we do our job right.

Testing the technology

By taking a holistic approach to integrating BEBs, we will mitigate many challenges this new technology presents. Once we have incorporated the BEBs and feel comfortable with their ability to support the community’s needs, we will consider bringing more of the technology onboard. But first, we want to be certain of what an efficient, effective BEB system looks like. Being able to bring sustainable transit options to the Denver area is exciting. Focus should be on readying the system to support them.


Henry Stopplecamp
Assistant General Manager, Capital Programs
Regional Transportation District

Henry Stopplecamp is the assistant general manager of capital programs for the RTD. He is responsible for all of the RTD’s capital and maintenance activities for its systemwide infrastructure. Over the past 22 years, he also has worked on all RTD capital expansion projects from the Southwest Rail Corridor to the FasTracks Program.

Contact him at