Alexander Dennis Enviro500 (3 Door): Singapore prototype in the UK

In 2019, British bus manufacturer Alexander Dennis secured a contract to construct 50 double-deck buses for the Singapore market. These buses were specifically designed with three doors and two staircases and are referred to as the Alexander Dennis Enviro500 (3 Door). They were put into passenger service starting in 2021.

In addition to the 50 buses deployed in Singapore, Alexander Dennis constructed a prototype unit, known as K509, prior to initiating mass production of the 50 buses. This prototype was manufactured at ADL’s facility in Zhuhai, China, and later transported back to the United Kingdom for additional testing and homologation purposes, where it currently resides.


Further reading: Alexander Dennis Enviro500 (3 Door)

On 25 April 2019, a Land Transport Authority (LTA) contract was awarded to Alexander Dennis for 50 three-door double-deck buses, at a sum of roughly ~S$34 million.

Tender specifications for the three-door double-deck bus call for one entrance and two exit doors and the rearmost exit door must be behind the rear axle. In addition, the bus has two staircases and is built with a low-floor design. Buses are also limited to a maximum length of 12.5 metres and had to be Euro VI-compliant.

These specifications prompted a redesign of the existing Enviro500 3-axle bus. Notably, a new powertrain layout was incorporated to enable the creation of a full-low-floor right-hand-drive bus, marking a first for ADL.

Prototype bus K509

Prior to building the 50 Enviro500 buses for Singapore, a pre-production unit (Chassis Number: SFD323CR1LCZ40038) was built by Alexander Dennis at its manufacturing facility in Zhuhai, China. This prototype bus was shipped to the United Kingdom for additional testing and homologation (i.e. type approval prior to registration).

The bus was photographed in the UK in a Facebook post on 17 September 2021, travelling along the M6 motorway (near Stafford). A year later, on 15 June 2022, an Alexander Dennis press release announcing the official opening of its new facility in Farnborough contained a photo of the prototype bus.

On 17-18 June 2023, the bus was exhibited at the Dennis Vehicle Extravaganza event organised by the Dennis Society, held at the Rural Life Living Museum in Tilford, Surrey. Photos in this article are credited to glitchFan2428.

The ADL Enviro500 prototype bus carries the internal designation K509, as mentioned in ADL’s accompanying write-up. This vehicle is specifically identified as a “Test & Development Prototype of the Enviro500.”

ADL had previously delivered 3-door Enviro500 units in left-hand-drive (LHD) specification to Transports publics de la région lausannoise (TL) and PostAuto in Switzerland; and to Berliner Verkehrsbetriebe (BVG) in Berlin, Germany. The 3-door right-hand-drive (RHD) specification for Singapore is a first for ADL.

Design and Exterior

In line with LTA specifications, the bus incorporates a fully airconditioned, 3-door twin staircase body design which allows for increased passenger comfort and smoother passenger flow during boarding and alighting. The bus also bears LTA’s standard Lush Green base livery, but without the SGBUS decals and secondary white/grey trim colours.

No significant differences are observed between the prototype and the production units in Singapore, a minor one being the presence of side-facing CCTV cameras on both rear sides of the prototype, which have been replaced by blindspot monitoring cameras on production units supplied by TNT Surveillance.

On the technical side, the bus is equipped with a Euro VI-compliant Mercedes-Benz OM936 LA engine rated at 260 kW, paired with a Voith four-speed automatic gearbox. The transverse-mounted engine helps to reduce the length of the rear overhang, and the rearmost axle is now the drive axle, not the middle axle as with other ADL Enviro500 buses.

In addition, active steering functionality was also implemented on the middle axle which reduces tire wear and improves low-speed manoeuvrability. The pivoted middle axle is evident in photos of the static display bus above.


The interior layout and fittings in the prototype bus are also identical to the production units. As a test and development prototype, some of these exposed components around the bus would otherwise be not present, or concealed behind body panels.

Step-free access is offered across the entire lower deck. Seats were supplied by Vogel Industrie, and door systems by Ventura. Two wheelchair bays are offered per LTA specifications.

Two staircases are fitted, with the front staircase located behind the driver’s cab, and the second staircase located at the rear. The rear staircase leads directly to the third door, greatly increasing the convenience for alighting passengers by allowing quick egress from the upper deck.

LTA-mandated subsystems are also installed, such as electronic display signs, passenger information displays, Advanced Driver Assistance Systems, and automatic passenger counters. However, locally-installed subsystems such as the Trapeze fleet management system and automated fare collection equipment are not present on the prototype.

Featured Video

Video by Youtuber glitchFan2428:

Manufacturing in Zhuhai

All of Singapore’s 3-door ADL Enviro500 buses are built in Zhuhai (China), by a collaboration between Alexander Dennis Limited and Zhuhai Guangtong. Established in 2011, the bodywork manufacturing and assembly partnership expanded to include chassis manufacturing in 2019, thus unifying most manufacturing and assembly work in Zhuhai.

Three-Door Buses compared

Main Article: 3-Door Buses compared: ADL Enviro500 and MAN A95 | Land Transport Guru

The procurement of two distinct models of 3-door double-deck buses by LTA allows for a comparison between the ADL Enviro500 and the MAN A95 (Euro VI). These buses employ significantly different approaches in achieving the 3-door bus design.

The design of the ADL Enviro500 stands out as superior due to its full-low-floor aisle and step-free access to the third door. In contrast, the 3-door MAN A95 features reduced headroom and steps leading to the third door, resulting from the decision not to redesign the drivetrain layout.

ADL Enviro500 3-door Prototype: Technical Specifications
Engine Mercedes-Benz OM 936 LA, 7698cc
Power/torque rating of 260 kW (354 hp) @ 1800 rpm / 1400 Nm @ 1200–1600 rpm
Emission Standard Euro VI-compliant
BlueTec® SCR diesel technology (with EGR), common-rail fuel injection system. Requires diesel exhaust fluids such as AdBlue.
Transmission Voith DIWA 864.6 gearbox, four-speed automatic
Bodywork Enviro500 3D2S Bodywork
Built and assembled in Zhuhai, China.
EDS LECIP Electronic Display Sign
Orange LED Matrix; Mounted on Front, Left side and Rear
PIDS LECIP OBC-VISION Passenger Information Display System
LED text displays, LCD display screens, interior speakers & exterior speaker
Driver Assistance TNT Surveillance T-Guard
– Forward collision warning system (T-FA Front Alert Camera)
Anti-Fatigue system (T-DA Driver Alert Camera)
Additional Features · TNT Surveillance T-APC automatic passenger counting system
· USB charging ports
· Ventura doors
· Denso air-conditioning
· Vogel Industrie System 750/3 seats

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