In-motion charging (IMC) electric bus, also known as a battery trolleybus or trolleybus with extended autonomous run, is an electrically powered public transport vehicle that draws power from an overhead contact network (catenary) via trolley poles while simultaneously charging an on-board traction battery. This technology allows the vehicle to operate continuously: drawing power and charging while under the overhead wires, and operating as a battery electric bus on sections of the route lacking this infrastructure.

This concept is an evolution of the traditional trolleybus, developing from vehicles with small auxiliary power units for emergency use to modern systems where vehicles can cover significant distances autonomously, often between .

IMC systems are being actively implemented by major metropolises (e.g., Beijing, Saint Petersburg, Mexico City) and in transport networks across developed countries (e.g. Switzerland, Germany, The Netherlands). Modern In-Motion Charging systems can offer significant cost advantages over fully battery-electric bus networks.

Studies indicate that upgrading existing trolleybus infrastructure to IMC can reduce capital costs for rolling stock by approximately 50% and lower operational expenses by around 20% over a 15-year lifecycle compared to new battery-electric bus fleets. When building an IMC system from scratch with partial overhead lines, capital expenditures can still be lower than a fully battery-based system, due to reduced battery capacity requirements, a smaller fleet size and eliminated downtime during charging.

Terminology The term In-Motion Charging (IMC) was introduced as a branding concept by Erik Lenz of Vossloh Kiepe (now Kiepe Electric) in 2014 during the trolley:motion conference in Hamburg. The terminology was intended to improve the public perception of trolleybuses by highlighting their key advantage over static-charging electric buses: the ability to recharge batteries while transporting passengers, eliminating stationary charging times.

In Germany, the term BOB (Batterie-Oberleitungs-Bus, Battery-Overhead-Bus) is also used by some operators, such as in Solingen. In Arnhem (Netherlands), the concept is often referred to as Trolley 2.0.

In Russia and CIS countries, these vehicles are often referred to as a Trolleybus with Extended Autonomous Run (, abbreviated as TUAH) or an Electrobus with dynamic charging.

History Gas or diesel powered dual mode buses

The concept of a trolleybus operating away from overhead wires dates back to the early 20th century. While the word trolleybus originates from 1882, when Werner von Siemens presented an early electrically powered vehicle, the idea of off-wire capability evolved to allow flexibility.

In the United States, the Public Service Company of New Jersey, in conjunction with the Yellow Coach Manufacturing Company, developed "All Service Vehicles" (ASVs) between 1935 and 1948. These were early trackless trolleys capable of operating as gas-electric buses when off-wire.

Before the maturation of high-capacity lithium batteries (which enable modern In-Motion Charging), term dual-mode bus was used for off-wire vehicles utilizing overhead wires for electric power and a separate, full-sized diesel engine for surface travel. Notable examples included: Seattle: King County Metro used special-order articulated Breda buses in the Downtown Seattle Transit Tunnel from 1990 to 2005. These vehicles operated as trolleybuses underground to eliminate diesel emissions in the tunnel, and switched to diesel engines for surface street operations. Boston: The Massachusetts Bay Transportation Authority (MBTA) used dual-mode buses on the Silver Line (Waterfront) route from 2004 until 2023. Similar to Seattle, the electric mode was utilized to manage air quality within the system's tunnels. They were eventually replaced by diesel hybrids and battery-electric buses.

From the 1980s onward, systems began purchasing trolleybuses equipped with auxiliary power units (APUs) — small diesel engines or batteries — to allow them to bypass route blockages or travel short distances without overhead lines, with notable adopters including Muni in San Francisco, TransLink in Vancouver, and Beijing. Examples include the approximately 300 vehicles in San Francisco and the trolleybuses used on the 2005-opened system in Rome, Italy,Webb, Mary (ed.) (2009). Jane's Urban Transport Systems 2009-2010, p. 195. Coulsdon (UK): Jane's Information Group. . which can run short distances on battery power before needing recharging, with Rome’s vehicles using batteries only on the final 500 metres of an 11.5-km route. Such vehicles are generally not considered dual-mode buses, but are also the precursors of IMC.

Shift to IMC With the development of battery technology (specifically Li-ion) in recent years, the focus shifted from diesel auxiliary units to purely electric autonomy. In Shanghai, experiments began in 2006 with "capacitor energy storage" electric buses that charged at stops. By the 2010s, the "TROLLEY project" in Central Europe was established to promote sustainable trolleybus strategies, leading to the widespread adoption of In-Motion Charging to extend routes without installing additional overhead wires. In 2018, Solaris Bus & Coach unveiled the "Trollino 24", a double-articulated 24-meter IMC bus designed for high-capacity routes, setting a benchmark for future BRT-style electric transit.

Technology

IMC trolleybuses are equipped with a high-capacity traction battery adapted to the route's specific requirements. The vehicle typically operates with a mix of wire connection and battery power (e.g., 60% of the time on the wire and 40% on battery).

Charging: Charging occurs while the vehicle is in motion under existing overhead wires. Current transfer can reach power levels of up to 500 kW (e.g., the IMC500 system). Range: Modern units can travel significant distances off-wire, often in excess of . Advantages: Unlike stationary charging electric buses (Opportunity Charging or Overnight Charging), IMC does not require long charging stops at terminals or the construction of dedicated charging stations in public spaces. It allows for the electrification of bus routes by extending existing trolleybus lines.

Comparison with other electric buses Feature Overnight Charging (ONC) Opportunity Charging (OC) In-Motion Charging (IMC) Charging Method Slow charging at the depot (overnight) Ultra-fast charging at specific stops Charging in motion if under overhead wires Infrastructure Requires high-power grid connections at depots Requires charging stations at stops/terminals Uses existing trolleybus network; no new chargers needed for extensions Downtime 4–10 hours (in depot) 5–25 minutes (at stops) None (charges while driving) Battery Size Large/Heavy (reduces passenger capacity) Moderate Moderate/Small Heating Often requires diesel heater in winter Electrical (limited) Electrical (powered by overhead wire) Grid Impact High peak load at night High spikes during fast charging Distributed load throughout the day

Some operational issues have been noted in systems such as Saint Petersburg and , where overheating of the contact wire can occur due to high charging currents if the vehicle is moving too slowly or is stationary while charging.

Automatic wiring and dewiring

A key feature of modern IMC systems is the ability to switch between overhead wire mode and battery mode without the driver leaving the cab. While older systems required manual manipulation of the trolley poles (using ropes), modern vehicles utilize automatic current collectors.

Dewiring: The driver can retract the trolley poles at any point, usually while the vehicle is in motion. Pneumatic or hydraulic systems pull the poles down to a locked position on the roof. Wiring: To reconnect to the grid, the vehicle typically stops or slows down at a specific location equipped with guiding funnels (also known as "catch pans", "wiredrops", or Einfädeltrichter in German). The driver activates the system, and the poles automatically rise; the funnels guide the collector shoes onto the contact wires.

Examples of this infrastructure in operation include: Solingen: Automatic wiring takes place at specific stops such as Burg Seilbahn and the Aufderhöhe bus station, where charging funnels were installed to support the extension of the network without continuous wiring. Zürich: Vehicles on routes like line 83 use threading funnels to reconnect to the network after running on battery power through complex intersections like Albisriederplatz. Naples: The system utilizes devices known locally as tegolini (little tiles) to guide the poles onto the bifilar wires after the automatic lifting mechanism is engaged. Other cities where such devices are used include Saint Petersburg, Prague and others.

Implementation strategies and operational models There are two fundamentally different approaches to the implementation of IMC, depending on whether the city has a trolleybus overhead contact network.

Existing overhead wire networks

Route extension This is the most common entry point for IMC technology. Transit operators utilize existing overhead wire networks to charge the vehicle, then lower the poles to extend service into new neighborhoods, suburbs, or developments where installing wires is difficult or too expensive. This model allows for the organic growth of the network using existing infrastructure.

Arnhem: As part of the "Trolley 2.0" initiative, the Dutch city utilized IMC to extend its reach regionally without building new infrastructure outside the urban core. On Line 352 connecting Arnhem to Wageningen, buses run under overhead wires for the first section to charge their batteries, then disconnect to cover the remaining intercity distance to the Wageningen bus station on battery power. : In 2023, Route 4 was launched using IMC technology to serve a new micro-district. The buses charge while driving under the old city network and switch to battery power to cover the non-electrified loop in the new residential area, saving significant infrastructure costs. Gdynia: The operator used IMC to extend line 31 to the Ergo Arena and line 29 to the Fikakowo district, areas previously unreachable by electric transit due to a lack of wiring.

Diesel replacement In this model, operators identify diesel bus routes that overlap significantly with existing trolleybus wires. By switching these lines to IMC vehicles, the bus can run under the wires for the shared portion of the journey (charging the battery) and run autonomously for the unique, non-wired section of the route. This eliminates diesel emissions without requiring new infrastructure.

Beijing: Between 2015 and 2016, several Bus Rapid Transit (BRT) lines were converted from diesel to dual-source trolleybuses. The vehicles charge while running in the dedicated BRT lanes and use batteries to navigate complex intersections or depot movements. Esslingen am Neckar: The city integrated bus lines 113 and 118 into the electric network. Buses use the existing catenary in the city center and switch to battery power to serve the districts of Berkheim and Zollberg. Minsk: The city has adopted a systematic policy of replacing diesel bus routes with IMC trolleybuses to utilize its extensive existing infrastructure. For example, in 2021, bus routes 56 and 90 were converted to trolleybus operation using vehicles with extended autonomous range, and in 2022, trolleybus route 22 was extended to replace bus routes 38 and 123.С 1 марта в Минске изменяются некоторые маршруты городского транспорта. blizko.by, «Близкие Новости»