Electric buses are coming to Pittsburgh. The Port Authority of Allegheny County (PAAC) introduced a handful of battery-electric buses to service in the past year, and has placed orders for additional electric buses to be used on the forthcoming bus rapid transit service between Downtown and Oakland. Around the country, transit agencies are ordering electric buses, and subsidies for electric buses may become significant to federal transportation policy. With all the recent buzz around electric buses, you could be forgiven for thinking electric buses are new technology—but they’ve actually been around for decades. Different to the battery-powered vehicles in the press today, trolleybuses—electric buses which draw power from overhead wires—were once far more prominent, though only survive in a few US cities (Boston, San Francisco, Seattle, Philadelphia, and Dayton). Returning to the trolleybus—aided by some advancements in battery technology—is the best way to electrify the United States’ bus fleet, and Pittsburgh happens to be a great place to start.

Quick aside on trolleybus history: Pittsburgh is actually somewhat unique in never having hosted trolleybuses. Many cities used trolleybuses as a sort of transition between streetcars and diesel buses, but Pittsburgh kept its streetcar network relatively late (into the 1960s) and went straight to diesel buses. However, nearby (but much smaller) western Pennsylvania city Johnstown did have a trolleybus network! (Ok, back to the point).

Trolleybus in Johnstown, PA, 1967.

Enter In-Motion Charging

In Europe, cities and bus manufacturers have been combining trolleybus and battery technology, to produce in-motion charging (IMC), described by transit writer and best practices expert Alon Levy in a really good post on their blog Pedestrian Observations (which was the inspiration for this post). As noted here, in-motion charging works best “when relatively small electrification projects can impact a large swath of bus routes. This, in turn, is most useful when one trunk splits into many branches.” Pittsburgh’s extremely radial, trunk-based bus network could be particularly well-suited to trolleybuses which use IMC: putting up wires on a few major corridors could bring pollution-free bus service to much of the city.

Trolleybuses For Pittsburgh

The most important variable in planning an IMC network is the off-wire range of the vehicles. Longer-range IMC buses on the road right now include Kiepe Electric’s buses in Solingen, Germany, with an off-wire range of 18 km (11 mi). Kiepe is supplying the electrical equipment for Dayton’s new trolleybuses, which have an off-wire range of 24 km (15 mi), according to Dayton’s Regional Transit Authority. For the purposes of this, the hypothetical Pittsburgh IMC bus has an off-wire range of 20 km, which seems optimistic against most IMC systems in operation (which average between 5-15 km off-wire), but is probably do-able given the range of more recent buses.

Prospective Pittsburgh trolleybus infrastructure map. Blue indicates first-priority corridors (explained below); green second-priority corridors. Map linked here.

So where should the city be stringing up trolley wires? Here are the four corridors that I think would be the strongest, and which, together, would bring all-electric bus service to a large swath of the city:

  • Fifth Avenue: Wiring Fifth Avenue between Downtown and Craig Street would be sufficient for the four main Fifth Avenue routes to complete their trips and return off-wire. (The 71A & B take two different routes to Highland Park, an approximately 10 km round-trip; the C & D go to Wilkinsburg, just over 14 km). The 71A and 71C could also pick up wires on Centre Avenue (see below) which would further shorten their off-wire segments.
  • Forbes Avenue: The Forbes Avenue routes branch further east, in Squirrel Hill, so wires should extend to Murray Avenue (also good because getting up said hill would be a not-insignificant battery drain). The 61D to the Waterfront mall—a 12.4 km round-trip—should be fine, and the 61B might just make it to Braddock and back (18.8 km), but the 61A and (especially) C are >20 km round-trips, so are difficult without opportunity chargers (more on this later) at their outer termini.
  • Liberty Avenue & Butler Street: Wiring the Liberty Avenue spine between Downtown and Lawrenceville, around 33rd Street, would provide enough power easily for the 88 (11 km) and maybe for the 86 (19.6 km, though this could have help along Centre Avenue) and 87 (18 km). You’d have to extend wires along Butler up to about 55th Street to bring the 91 just within round-trip range; this is a bit far, but might be worth it because this section is shared with the circumferential 93 and the 87 (which would bring that route within safe all-electric range).
  • Centre Avenue: Between Downtown and East Liberty, Centre Avenue hosts several bus routes, and contains some significant gradients in the Hill District, which make it ideal as a trolleybus corridor. Wiring Centre Avenue as far as Negley or Euclid would provide sufficient power for the 82, and shorter sections of power for many more routes: the 54, 71A/C, 81, 83, and 86 all have segments on Centre Avenue and, with wires on other sections of their routes, could be made fully-electric.

With the four corridors above, much of Pittsburgh’s East End would have fully-electric, pollution-free bus service. You may (rightly) point out that this proposed list is very East End-biased—this is really where the trunk/branch structure is strongest. In other areas of the city, the trunks are shorter and the branches longer, less desirable for IMC: this includes Carson Street in the West End and South Side, and North Avenue in the Central Northside.

There are other corridors that would work. Wiring Second Avenue as far as the Pittsburgh Technology Center could make the 57, 58, and (maybe) 56 fully-electric; Murray Avenue hosts frequent service and is hilly so may be worth it. Short but busy sections of route where buses’ boarding times are long, such as Penn Avenue in East Liberty, can also work for IMC.

The busways are the most glaring omission above—the reason they were left out above is because they are a real mixed bag of branch lengths, but enough branches could work with opportunity chargers at termini. If these were available, the busways would, of course, be very attractive routes for electrification—there are already several busway branches, such as the P17, P71, and G31, which are within the 20 km off-wire range. The other omission is the South Hills routes: these share a trunk (the Mount Washington Tunnel), but that is already wired for light rail, and trolleybus and light rail wires are not electrically compatible (trolleybuses need a separate return wire, rail vehicles do this through the running rails and therefore do not).

Opportunity Charging

Opportunity charging refers to the ability of vehicles to recharge briefly while they sit in one place, either at certain bus stops or at a terminal. The required infrastructure is a short section of wire which buses can connect to while standing, as employed in Solingen, Germany, and being considered in Gdynia, Poland. Placing opportunity chargers at terminals effectively doubles the off-wire distance that vehicles can travel, as they would only need enough battery power to make it to the terminal, rather than to the terminal and back to the wires. Opportunity chargers would allow, for example, the 61A & B to run to their terminals in Braddock (11.8 and 9.4km from Squirrel Hill, respectively), and the 61C to its terminal in McKeesport (15.9km). This would also open up several East Busway branches—including the P67 (a 9.7 km branch), P7 (14.7 km), and P68 (19.7 km)—to IMC operation, as well as the remaining West Busway branches, the G3 (16.9 km), and (maybe) the 28X (22.2 km).

Why We Should Want Trolleybuses

Surely—you may be thinking—battery-powered buses could do this just as easily? And if they can’t now, at the rate technology progresses, in a few years’ time they might—so won’t all these wires will have been wasteful? Nope! There are several key, fundamental advantages of trolleybuses over batteries.

IMC buses recharge their batteries while in service. This is a major difference with exclusively battery-powered vehicles, which need to stop and recharge with sufficient power to complete their next trip. This can take place at terminals, but only where terminal layovers are long enough to fully recharge; otherwise, battery buses have to be removed from service for some amount of time in order to recharge. The lack of ability for battery buses to recharge in service also means their batteries—a significant portion of the cost of an electric bus—need to be larger than those of an IMC vehicle. Battery-only vehicles are also less resilient: the range of battery-electric buses has been shown to suffer in cold weather and on steep hills—two things Pittsburgh is infamous for having in large amounts.

Most importantly, trolleybuses are extremely well-proven technology. Cities around the world have operated trolleybuses for over a century, and there are numerous long-standing precedents from which Pittsburgh (or any other city) can draw best practices on trolleybus operation. Philadelphia’s pilot of battery-electric buses has come to a halt, while its 98-year-old trolleybus network soldiers on. Dayton has operated trolleybuses since 1933 and, as mentioned above, has recently invested millions in its continued operation. And these are just the two examples nearest to Pittsburgh—looking internationally can provide further guidance on trolleybus operations, especially with the addition of in-motion and opportunity charging.

Re-Embracing The Trolleybus

If we want to develop or expand trolleybus and IMC networks, we have to encourage them. Right now, the Federal Transit Authority (FTA) subsidizes purchases of battery-electric (as well as fuel cell and hybrid) buses through its Low or No Emission Vehicle Program. But this program doesn’t cover the infrastructure costs of hanging new trolleybus wires. As “fixed guideway” projects, agencies building new trolleybus wires need to apply for FTA Capital Investment Grants instead, placing them in competition with rail transit projects. This should be changed. The Clean Transit For America Act, which increases funding to the Low or No Emission Vehicle Program, should change the guidelines of the program to include trolleybus/IMC vehicles, as well as the cost of wiring. This is an important policy change not only on the off-chance that a city like Pittsburgh decides to develop a new trolleybus network—but because the strategy for bus electrification in existing trolleybus cities should be extending wires, not scrapping them for batteries, as Boston seems worryingly to be considering.

PAAC’s first battery-electric buses, courtesy of the Pittsburgh Post-Gazette

IMC can create a “best of both worlds” electric bus, mitigating the logistical issues with battery-electric buses while keeping their off-wire flexibility—and electrifying a lot of bus service without the cost of wiring every bus route in their entirety. The point of this post was not to say that battery-electric technology is bad; after all, it is advancements in battery tech that allow IMC to work, and which will allow it to improve in the coming years. But electrification of buses is imperative for the climate and for public health. There’s no time to wait for battery technology to advance to the point where it is able to carry an entire city’s bus fleet, at reasonable cost and with acceptable reliability. If we want large-scale bus electrification soon, it is time to re-embrace the trolleybus.

Join the Conversation


  1. I agree that using trolley wires power the buses, either for traction or for charging, is more viable for a heavy duty bus system than using a battery and only charge while in the terminal or in the depot. However, I want to say in motion charging is not always a good idea for bus routes that runs a long distance off wire, especially on hills. The much smaller batteries on IMC vehicles are simply not that capable, and their performance might degrade quicker than a battery bus. If we have to do a long (20km) off-wire trip every time, a battery system for a much longer distance is needed (considering the weather factor and battery life).

    Solingen is a good example of using battery hybrid on trolleybuses, but the new cars only entered the service in 2018, so I can’t find more information on the long term battery performance and cost. But in other systems where IMC is already in use for a longer time, the buses did not perform as expected. A example was trolleybus system in Hangzhou, they began to use IMC vehicles since 2013, when a section of existing catenary for route 151 / 155 was removed. The section has a length of 2.4 km one-way, despite because of rerouting, the section of unelectrified gap for route 155 increased to 6 km one-way. (The buses still run and layover at both end of the route and the terminal with catenary.) Later the trolleybuses have been used on route 153 (with a 8 km off wire section, including the layover;) and route 188 (wih a 5 km off wire section one-way).

    The first issue with the system is battery life. Despite claiming that the vehicles are capable of doing 80 km off-wire with HVAC on, the vehicle battery performance degraded quickly through 5 years. In 2018, the initial fleet, purchased in 2013, had to be retired early because their batterys are unusable anymore. (A battery replacement was not considered due to unknown reasons. However the replacement cost for lithium batterys are still high.) The second batch of trolleys, purchased in 2015, also has serious battery issues. It has been reported that on some vehicles, the battery can only be discharged to 55% before running out of power, and charging is also slowed so much that the drivers have to shut down equipments at terminal to facilitate charging. In addition, route 153, which requires the longest off wire section, had suffered from unreliable battery issues began in winter 2016 (using new 2015 built trolleybuses), when the charging became too slow for the trolleybus to make the off wire section. Route 153 and 188 later returned to diesel / CNG services.

    Another with the system is the unwired section between depot and catenary system. There are two depots on the system, one located on-wire with a capacity of 35 trolleybuses. The second one is located 7 km off-wire with no catenary system, so the buses cannot be charged in the depot. It has long been reported that in order to make the 7 km trip back to depot and return on wire, drivers have to do additional charging on wire before returning to the depot. Recently the second bus depot has been “re-developed”, so the buses have been moved to a newly constructed EV only depot located 12 km off-wire, which means a minimum of 24 km off-wire distance is required. It has been said that most trolleybus cannot travel that far off wire, and therefore trolleybuses located in the destroyed depot are going to be mothballed, only 6 years after initial purchase.

    Attempts have been made to improve the utilization of these 2015 built trolleybuses, but with long off-wire sections, they are not successful. After trolleybuses left route 153 / 188, the bus operator attempted to run the remaining trolleybuses on 160 (requiring a 7 km off-wire section, including layover) and 1005M (have 5 seperate off-wire sections, each about 1 – 3 km long). However, route 160 has the same issue a long off-wire section, while the small off-wire sections on 1005M causes consistent battery charging / discharging cycles (and drivers simply hate re-wire 5 times on a round trip, so sometimes they may skip some wired sections, causing more battery consumption and hurt the battery life). Trolleybuses on route 160 and 1005M have been replaced by battery buses recently.

    Therefore, I still believe trolleybuses have to utilize the catenary system as long as the road condition permits. The Gillig BRTs used in Dayton, as well as XT40/60s used in SF / Seattle, exclusively uses their batteries for short distance maneuver in case of emergency. These short distance batteries, despite being rated for > 20 km, might struggle on periodic off-wire section much shorter than their ratings. A consistent charging / discharging cycle during daily operations would also consume the battery life, even faster than a battery powered bus. The drivers might also overuse the off-wire capabilities for trolleybuses, which further facilites the consumption of battery life, in addition to risking draining their batteries on the off-wire section.

    For the high-density corridors in Pittsburgh, it makes perfect sence to install the catenary systems towards their terminal, rather than only electrify some shared sections between roads. In fact, the ridership on these routes are already sufficient to support a trolleybus system. 61A / B has a combined weekday ridership of 8.5k, with 61C / D has a combined weekday ridership of 11k. 71A / B / C / D all have a ridership count about 4.5k to 5.5k. Route 91 and 88 are more dense than the branching 61 and 71s.

    In addition, the cost for trolley wire installations might not be significantly reduced if the buses must charge in motion on their every trip. This requires additional capacity on the power transmission / rectify equipments on the section. Extending the catenary system is unlikely to add more requirements to the power transmission / rectify equipments, considering the battery charging demand is reduced. Additionally, most of the roads on trolleybus corridors will have utility poles in place, saving the need to build new trolley poles. The additional cost will mostly be the additional catenary wires installed, which only makes up a small proportion of the construction cost for a trolleybus system.

    On the east side of Pittsburgh, most of the buses use East Liberty garage. It is about 5 km from the proposed Strip District / Lawrenceville corridor, about 3 km from Murray / Forbes intersection, about 8 km from 61A / B terminal at Braddock, and further for 56 / 57 / 58 / 61C / 61D. This distance is simply not acceptable for depot operations, especially considering it is unlikely for PAT to restructure the East Liberty garage to install trolley wires (the buses can be charged by a plug-in cable, but the capacity is very limited). Therefore installing additional trolley wires to allow buses to travel on-wire to and from East Liberty depot is also important, especially considering it is unlikely the garage will be electrified. This is another reason to install wires on the Penn Avenue, serving the full length of 88 and 71C.

    IMC is a good idea for lightly used branch routes, but using too much off-wire sections on heavily used trunk routes would generate significant operational risk and additional cost related to battery life and reliability. For heavy duty bus lines, I think they should be electrified fully, from terminal to terminal, except very small sections where the infrastructure disallows the installation of catenary system (like low bridges).

    Liked by 1 person

    1. By the way, the South Hill tunnel might still be used for trolleybuses, if the bus height permits. Like the Market Street in SF uses a shared catenary system for trolleys and trolleybuses, the South Hill transit tunnel can also be electrified by simply constructing a dedicated return wire on the side of the existing wire (but the voltage must be compatible. The T’s 650V electrification is not usual for trolleybuses). The only technical requirement is leaving the return wire far enough so the pantograph won’t be able to touch two wires together.

      Liked by 1 person

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