Cities “Pave the Way” for Transportation ElectrificationPosted to Electric Power Research Institute (EPRI)
image credit: Three electric bus chargers at a park-and-ride in Bellevue, just east of Seattle. Photo courtesy of Danny Ilioiu.
- Aug 26, 2020 9:36 pm GMTAug 26, 2020 7:06 pm GMT
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A transformation is underway in New York City’s transportation system, though many people may not have noticed. Since 2018, a pilot fleet of ten battery-powered electric buses has been transporting passengers along routes such as 42nd Street. The quiet, zero-emission vehicles are part of a plan to convert the city’s 5,800 buses to electric.
The collaborative project between EPRI and the New York City Transit Authority aims to inform a phased electrification strategy, with 15 buses delivered in 2020 and another 45 currently in the process of being purchased. In January, EPRI reported on lessons learned and experiences in the project.
“We analyzed on-route charging and charging at depots after shifts, considering control strategies, electrical service impacts, and local grid impacts,” said Mark Kosowski, an expert on commercial and industrial transportation at EPRI.
New York is not alone. According to an EPRI study published in August 2019, more than 150 electric transit bus pilots or programs are underway in the United States. Examples include Louisville, Kentucky, Seattle, Boston, and Chicago. Each municipality is customizing its pilot to fit its own needs.
“Different agencies are looking for different outcomes from their pilot programs,” said Danny Ilioiu, who manages transit fleet electrification at King County Metro, which serves Seattle, Washington.
Some agencies are comparing the mileage of different technologies, some are examining various configurations of routes and charging facilities, and some seek to reduce air pollution in historically underserved areas.
“We’re deploying electric buses in south King County earlier than in other parts of the county. The south has historically been a fairly industrial area,” said Ilioiu. “This is where people with the lowest incomes live, and they’re the most affected by air pollution. It makes sense to start our transition to clean energy there.”
Marc Manning, who directs vehicle engineering and acquisition for Los Angeles County Metropolitan Transportation Authority, is working on a plan to convert the city’s entire bus network to zeroemission vehicles by 2030. The city’s pilot program will use some 600-kilowatt chargers that have the largest voltage range among commercially available products in the United States. Different sized batteries are charged at different voltages, so a charger with a large range can provide versatility for municipal transit agencies.
Municipal projects to deploy new electric buses, terminals, and charging infrastructure can be complex, requiring consideration of numerous requirements along with involvement of various agencies and organizations. These include architectural requirements of public design commissions; building codes; federal, state, and local street design requirements; National Electric Code requirements; and local utility requirements.
“When cities are planning these projects, they need to engage with their local utilities to determine whether electricity is available for new infrastructure,” said Kosowski. “If existing grid capacity is not sufficient, cities need to coordinate with the utility on grid upgrades.”
“I expect transit buses to be one of the first sectors to be fully electrified,” said Manning. “I think buses will help pave the way for other industries, like heavy-duty trucks.”
The Big Apple
The New York project tested two brands of buses with different charging requirements. Five New Flyer buses with 150 kilowatt-hour batteries ran the 42nd Street route across midtown Manhattan. The other five buses from Proterra use 440 kilowatt-hour batteries and ran routes between Manhattan, Queens, and Brooklyn.
“One important question we were trying to answer was, where do we want depot charging and where do we want on-route charging? Are there characteristics of routes that make one preferable? We also wanted to figure out whether larger or smaller batteries were preferable,” said Kosowski.
Before running the buses, the team spent more than six months building depot and on-route charging infrastructure. Construction of three on-route chargers on curbs in Manhattan and Brooklyn required coordination with many city departments. There were engineering challenges. For example, the surface of a steep street section on the East Side of Manhattan had a convex shape—lower near the curbs and higher in the middle of the street. The team had to repave the area so that the bus could make contact with the on-route charger.
The on-route chargers for the New Flyer buses range from 280 to 350 kilowatts depending on the capacity of the local grid circuits. The New Flyer buses used on-route chargers as well as two 60-kilowatt chargers at a bus depot on Manhattan’s West Side. Because the New Flyer buses charge at 800 volts and the Proterra buses at 400 volts, their routes had different brands and sizes of chargers.
The on-route chargers on 42nd Street look like giant modern desklamps. Buses stop underneath, and two long flat conductors are lowered onto the roof of the bus. The ten-minute charge is enough to drive the bus 10 to 12 miles, averaging 3 miles per hour. The bus operator charges several times a day while taking breaks or loading passengers. This charging system uses the new SAE J3105-1 recommended practice for EV charging systems with infrastructure mounted cross-rail connections.
The Proterra buses had larger batteries than the New Flyer models and were usually charged overnight with one of six 50-kilowatt chargers at the Queens depot. The team built an on-route 500-kilowatt charging system for the Proterra buses in Brooklyn, working with local utility Consolidated Edison to install a transformer needed to connect the system to the grid.
The Brooklyn charging system required coordinating with city agencies to comply with building codes and public and street design requirements. For example, the New York City Transit Authority spent about $500,000 to design and build enclosures for the charging equipment, and the agency integrated street furniture (benches) into the enclosures.
The team tracked driving times and routes and calculated a travel effectiveness metric. This is obtained by dividing the total travel distance by the total time, which includes all driving and charging from the bus’s first charge to the end of its shift. They found that on-route charging with small batteries has a travel effectiveness comparable to that of depot charging with large batteries.
The Emerald City
As part of its initiative to convert a fleet of 1,400 diesel-electric hybrid buses to all-electric buses, King County Metro in 2019 assembled a pilot fleet of 10 New Flyer, Proterra, and BYD buses. Two of the New Flyer buses initially did not meet all the agency’s needs due to the battery location.
“We didn’t like the fact that New Flyer buses have batteries inside the passenger seating area,” said Ilioiu. “So we worked with New Flyer to identify a battery technology that could be installed on the roof of the bus.”
King County Metro wanted buses with a driving range of 140 miles so that it could replace its diesel-electric hybrid buses with battery electric models without having to change its routes. Most routes don’t exceed that distance, but some routes are up to 300 miles.
“When we started this effort, we tried to answer a question that often comes up in the industry, which is, can I replace a diesel bus with an electric bus one for one?” said Ilioiu. “That appears to be the case with 70% of our routes. And the other 30% could potentially be satisfied by new battery or charging technology coming out in the next 10 to 15 years.”
The test fleet includes 40-foot buses and 60-foot articulated buses (vehicles with two or more sections connected by pivoting joints), which are operated as demand requires. The agency is arranging chargers in the transit centers such that either type of bus will fit.
King Country Metro also has 174 electric trolley buses that run on a wired grid. The agency might add more trolleys because they are better than the battery electric buses at climbing hills. Expanding the wired grid may also be cheaper than building charging stations in some parts of the network.
Ilioiu said that other transit agencies with electrification plans should keep in mind that while the drivetrain of electric buses may have lower maintenance needs than the drivetrain of diesel buses, the maintenance requirements of other bus systems (such as doors) are comparable across electric and diesel.
“It’s important to partner with the local utility on transit electrification,” said Ilioiu. “They have expertise in high-voltage systems. They have plans for grid upgrades and replacements and can coordinate with you on those projects. If they’re already planning an upgrade that can work with your new chargers, you might not have to foot the whole upgrade bill.”
The City of Angels
Since 2017, the Los Angeles County Metropolitan Transportation Authority (LA Metro) has been converting its natural gas–powered Orange and Silver Lines to electric buses with on-route charging. Out of an $88 million budget to convert the Orange Line to electric with 5 BYD and 40 New Flyer buses, the agency spent $14 million to deploy the necessary charging infrastructure.
LA Metro started by equipping the Orange Line’s North Hollywood Station with four 450-kilowatt chargers for on-route charging. The agency also will install up to 10 150-kilowatt depot chargers at its Division 8 maintenance yard.
In the time it has taken to fund and build the North Hollywood depot chargers, technology has advanced enough that LA Metro can now install 600-kilowatt depot chargers (with a larger voltage range) on the Orange Line’s Canoga and Chatsworth stations. The 450-kilowatt chargers work with the New Flyer buses, and the larger chargers can charge both New Flyer and BYD buses.
According to Manning, LA Metro decided to electrify the rapid transit Orange and Silver Lines first because the projects would have the least operational impact and the fewest technical hurdles. Although the Orange Line has to stop for cross-traffic, it has its own dedicated lanes, and buses stop about every mile along its 18-mile route. The Silver Line often uses high-occupancy toll lanes. Other LA Metro lines have a greater tendency to interfere with car traffic, and bus stops often create a line of vehicles behind them.
Converting the fleet will likely require adding grid capacity and navigating space constraints when constructing new infrastructure. As LA Metro switches from natural gas to electricity, it will need to negotiate with utilities on charging rates, said Manning.
City pilot program managers across the U.S. frequently share experiences and lessons learned, helping them navigate unexpected challenges. “One thing you have to expect with electric bus pilots is that there are going to be some unknowns,” said King County Metro’s Ilioiu.