Diesel engine out, electric powertrain in: 18 double-decker sightseeing buses belonging to Willms Touristik have recently been converted from diesel to electric. The modernised buses have been operating in Cologne and other German cities since the spring of 2025. All vehicles are powered by a powerful 145 kW electric motor coupled to an Allison T280R fully automatic transmission. Investing in an entirely new fleet of electric buses would not have been financially viable for the medium-sized company. As a result, Willms tendered for a funding program from the German Federal Ministry for Digital and Transport and was awarded the contract to convert its fleet of double-decker buses from diesel to electric. During the retrofit, the existing double-decker buses, which were manufactured between 1988 and 2019, were converted from diesel to a highly efficient electric drive.

Cologne, Germany, August 2025 – Instead of diesel engines, the bright red ‘CityTour’ convertible double-decker buses from Willms Touristik now operate almost silently through the narrow streets of Cologne city center, thanks to their new electric drives. Moreover, with the Continuous Power Technology™ from the Allison transmissions they set off as smoothly and jolt-free as if running on rails. Thanks to a multi-million Euro grant from the German Federal Ministry for Digital and Transport, Willms was able to convert its city tour bus fleet to electric drive. As part of the ‘Retrofit electric mobility in urban public transport' funding program, 18 MAN double-deckers were converted from diesel to electric drive. The conversion was carried out by Banke ApS, a Danish specialist company, in close cooperation with the Allison authorized distributor DGS Diesel- und Getriebeservice GmbH from Mainz, Germany.

The converted buses comprised six different models on MAN chassis. They range from 37-year-old MAN SD202s (built between 1988 and 1990) to modern Euro 6 buses from 2016 to 2019.

First of all, the vehicles were completely stripped down: The entire diesel powertrain including the combustion engine, exhaust system, fuel tanks and conventional transmission were removed. Following a rigorous inspection of the chassis, the new electrical components were installed. The heart of the drive is a DANA TM4 SUMO HP electric motor delivering 145 kW and 625 Nm in continuous operation. Power is transmitted by the fully automatic six-speed T280R transmission from Allison Transmission. Six lithium iron phosphate battery packs with a total storage capacity of 240 kWh enable a range of around 200 kilometers (approx. 124 miles), which is sufficient for the daily city sightseeing tours.

Since the city tours use buses with an open top deck, the batteries could not be placed on the roof as in conventional buses. Instead, each vehicle has six battery packs fitted in the rear as well as in the passenger compartment. Depending on the bus model, this eliminates between two and six passenger seats.

Conversion to Electric: The Right Decision

Bus operator Sascha Willms is highly satisfied with his 'new' electric buses. He is particularly impressed by the driving comfort provided by the Allison transmissions: "The acceleration is smooth, the maneuverability is excellent and there are no jolts when shifting gears. I also anticipate that beyond the fully hydraulic transmission, the electric drive will eliminate wear and tear and high maintenance costs for the components.

It was particularly important for Willms Touristik to use a drive system that offers a high level of robustness, particularly in view of the demanding conditions endured by a sightseeing bus. "We deliberately decided against a gearless direct drive and instead selected a drive system that has already proven itself in municipal vehicles, such as refuse collection vehicles." The central engine design that has now been implemented in combination with the six-speed Allison fully automatic transmission completely fulfills these requirements.

Karsten Flamming, executive assistant at Willms, notes: "In addition, the fully automatic transmission ensures a greater range and fewer charging stops. Without a transmission, the electric motor would run at a constant high speed and consume significantly more electricity. The Allison transmission shifts automatically so that the engine runs at lower speeds, hence allowing us to be more energy-efficient while driving."

Although converting existing buses is significantly cheaper than purchasing new vehicles, Willms would not have been able to convert its double-decker fleet to electric drive without the funding of the German Federal Ministry for Digital and Transport. "It was only thanks to this funding program that our company was able to convert so many buses to electric drive in such a short space of time. 80 per cent of the conversion costs are covered by the Federal Ministry for Digital and Transport. We at Willms Touristik are bearing the remaining cost of around 2.2 million euros - including setting up the charging infrastructure, driver training and further training for our workshop staff. That may sound like a large sum, but we didn't have to buy any new buses and instead we now have a modernized fleet that will be running for many years to come."

"Considering that diesel buses will probably be forbidden from driving in German city centers in a few years' time, this project is not only an important step towards CO₂-free mobility, but also crucial for the future viability and profitability of our company," explains Sascha Wilms.

He generally considers the conversion from diesel to electric buses to be a sensible alternative to purchasing new buses. "In general, sightseeing buses are in service two to three times as long as conventional city buses. Ergo, even our 'oldtimer' buses built in 1988 and 1990 still have many years of service ahead of them. Replacing them with new vehicles would not have been economically sensible, especially as the investment in a retrofit is significantly cheaper."

The conversion isn't merely economical, it also makes ecological sense by reducing local pollutant emissions and saving resources because no new vehicles need to be built.

Energy costs for electric buses are around 45% lower than for diesel buses. Especially when travelling on highways, energy consumption is low at only about 0.75 kWh per kilometer. Willms calculates an average energy consumption of 1.1 kWh per kilometer. This is around 0.33 euros per kilometer in electricity costs compared to around 0.60 euros per kilometer, previously, with diesel.

More Comfort and Improved Air Quality

The new electric buses run much more quietly and with less vibration than their diesel-powered predecessors. The noise level has been reduced by up to 10 decibels. As there is no annoying engine hum, passengers can hear the explanations through their headphones much better.

The drivers particularly appreciate the simplified operation: one pedal for the accelerator, one for the brake - the fully automatic Allison transmission shifts automatically and ensures a smooth start-up, constant acceleration and full control, even in dense city traffic.

Given that the electric buses no longer emit any pollutants, they boost air quality in the city center. This is particularly noticeable in Cologne's numerous tunnels. Passengers and residents benefit from the significantly reduced noise and pollution levels. "In the past, my drivers were often asked why the smelly diesel vehicles were still being used in the city center," reports Willms, "I'm glad that's over now. The drivers are very happy with the vehicles. The easy, quick start-up and smooth ride have made operating the vehicles much more pleasant and stress-free."

More Efficiency and Performance with Fully Automatic Transmission

The driving characteristics of the converted double-decker buses differ significantly from those of conventional, diesel-powered buses with manual or automated gearboxes. Passengers, especially on the upper deck, benefit from the fact that the jerky gear changes that can occur with other transmission technologies are eliminated. This is made possible by Allison's Continuous Power Technology. The technology smoothly multiplies high engine torque, delivering more power to the vehicle's wheels. This allows for full-power shifts and enables improved acceleration.

The Allison T280R transmission was originally developed for diesel buses. Experts at Banke ApS and DGS have adapted it specifically for use in electric buses in order to make optimum use of the electric motor and further increase the efficiency of the overall system.

Project planning and technical support for electric vehicles in Germany is managed by Allison’s authorized distributor DGS Diesel- und Getriebeservice GmbH in Mainz.

Christian Bock, Area Sales Manager at Allison Transmission, explains: "This drive solution is ideal for inner-city traffic as it contributes significantly to climate protection. The versatility of Allison transmissions is once again evident here. They not only work with diesel engines, but also with alternative fuels and alternative drive systems. Our fully automatic transmissions are perfectly suited for vehicles with natural gas, hydrogen or electric drives."

With this project, Allison is underlining its leading role in the field of sustainable mobility solutions. The wide range of propulsion technologies can be seamlessly combined with alternative fuels and modern drive systems.