Alexander Dennis Enviro500 (3 Door)

Alexander Dennis Enviro500 (3 Door)
Manufacturer Alexander Dennis Limited (ADL)
Bodywork Enviro500 3D2S
Years in operation 2021–
Operators SBS Transit
SMRT Buses
Tower Transit
Technical Data
Length 12.5 metre
Engine Mercedes-Benz OM 936 LA
Transmission Voith DIWA 864.6
Accessibility Low Floor & Wheelchair-accessible
Emission Standard Euro VI (EGR+SCR)

The Alexander Dennis Enviro500 3-Door is a double-deck bus model procured by the Land Transport Authority in April 2019. 50 units were purchased, specially configured with three doors and two staircases for smoother boarding and alighting. These are also the first 3-door Enviro500 buses to be designed for the right-hand-drive market.

ADL delivered 50 of these buses to Singapore’s Land Transport Authority under Contract PT342 (Procurement of 3-Door Euro 6 Double Deck Diesel Buses), awarded for ~S$34 million. Another 50 buses, the MAN A95 (Euro 6) – 3-Door, were delivered by ST Engineering. Both bus types were initially expected to enter revenue service in 2020, but were delayed to 2021.

Buses made their revenue service debut on 26 October 2021, operating on Bus Services 190 & 974. They join an operational fleet of 216 ADL Enviro500 (Euro V) public buses in Singapore.

Prior to the introduction of these buses, a one-off Alexander Dennis Enviro500 (3-Door) Concept Bus was commissioned by the LTA as a static display. It was first exhibited to the public in March 2016, and later received an upgraded new air-conditioning system in 2018 for use as a permanent display, with minor modifications to the bus cabin.

Design Features

The bus features a full-flat floor design along with three passenger doors and two staircases, allowing commuters to move through the vehicle quickly and safely. It will also use the latest aluminium composite body technology and a host of new safety and energy-saving features.

The rearmost axle is used as the drive axle, which differs from the standard Enviro500 offering where the middle axle is the drive axle. Significant redesign work was likely involved in relocating the engine and drivetrain components to the right, accommodating the right-hand-drive, full-low-floor layout.

Alexander Dennis Enviro500 (Euro 6) – 3-Door Batch

Buses were progressively delivered to Singapore starting in May 2021, with the first unit registered in September 2021. The 50 buses are registered as SG6333M – SG6382X.

The first unit(s) registered to the various Public Transport Operators were:

  • SMRT Buses – SG6349T (21 Sep 2021)
  • SBS Transit – SG6338A (21 Sep 2021)
  • Tower Transit – SG6341P (2 Dec 2021)
Basic Technical Specifications
Length x Width x Height: 12500 mm x 2550 mm x 4300 mm
2.5m front and 3.23m rear overhang
5.22m and 1.55m wheelbases
Weights 26,000kg GVW / 15,590kg UW
2.03m Lower Deck / 1.81m Upper Deck
ZF RL75A front axle / ZF RL82A steered tag axle / ZF AV133 drive axle
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
Both chassis and bodywork built and assembled in Zhuhai, China. Shipped completely-built-up (CBU) to Singapore.
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)
– Side collision warning system (Side Alert Cameras)
Anti-Fatigue system (T-DA Driver Alert Camera)
– T-SEEDS telematics system
Additional Features · TNT Surveillance T-APC automatic passenger counting system
· USB charging ports
· Stroller restraint system
· Ventura doors
· Denso air-conditioning
· Vogel Industrie System 750/3 seats
Licensed Capacity Seating (Upper deck): 51 | Seating (Lower deck): 18 | Standing: 63 | Total: 132
Not including 2 foldable seats, 2 wheelchair bays

Buses made their debut on 26 October 2021, operating on Bus Services 190 & 974.


Contract PT342 (Procurement of 3-Door Euro 6 Double Deck Diesel Buses) was published by the Land Transport Authority (LTA) on 15 May 2018, and awarded on 25 April 2019. Alexander Dennis and ST Engineering Land Systems would deliver 50 buses each, namely the ADL Enviro500 and the MAN A95 (Euro 6).

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. These buses are also Euro 6 (or Euro VI)-compliant, representing the latest in emission standards which came into effect on 1 January 2018 for all new diesel vehicles registered in Singapore.

Existing LTA requirements for new buses include two wheelchair bays; a Passenger Information Display System (PIDS) comprising LED text displays, LCD display screens and interior speakers; Advanced Driver Assistance System and Anti-Fatigue system; high-definition CCTV cameras; and automatic passenger counters at entrance and exit doors of the bus.

Transition to clean energy bus fleet

The 100 three-door double-deck buses under Contract PT342 are the last pure-diesel buses to be procured for the Singapore public bus industry.

Authorities announced during the Committee of Supply Debate 2019 that Singapore would commit to a 100% clean energy bus fleet by 2040. This commitment was further reaffirmed in the Committee of Supply Debate 2020 held in March, where it was announced that only electric or hybrid buses would henceforth be procured in line with this clean energy goal.

Design Features & Challenges

Prior to this tender, European bus manufacturers typically made fully-low-floor chassis targeted at their domestic left-hand-drive (LHD)-dominant market. As a result, drivetrain components are offset to the left of the chassis to accommodate a full-low-floor design and an optional third door at the rear. Given that the tender called for a right-hand-drive (RHD), full-low-floor diesel bus with a third door at the rear overhang, bus manufacturers faced the challenge of modifying existing designs to fulfil this (relatively) small batch of buses in the most economical way.

Alexander Dennis Limited (ADL) had relocated the engine and drivetrain components of the Enviro500 (3-door) buses to the right rear of the chassis, likely requiring significant engineering effort. This new powertrain layout allows for a full-low-floor right-hand-drive bus, the first of its kind for ADL.

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. While Enviro500 buses typically feature Cummins engines, the BVG units are fitted with the Mercedes-Benz OM936 engine from Daimler. The 3-door Enviro500 buses for the Singapore market also feature the same Mercedes-Benz engine, which is identical to that in the Mercedes-Benz Citaro hybrid.

The ADL Enviro500 (3 Door) has opted for a transverse engine layout, similar to that of the Volvo B9TL. The rear axle is now the drive axle, instead of the middle axle. This was previously identified in the concept renders released by ADL shortly after the announcement of the tender result in 2019, and has since been confirmed to be so, based on pictures of the actual bus. In addition, steering functionality was also implemented on the middle axle to decrease tire wear and improve low-speed manoeuvrability. This appears to be actively steered, rather than the passive steering feature previously fitted to the retired Volvo Olympian (3-axle).

Three-Door Buses compared

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

With two different bus models procured by LTA, the ADL and MAN 3-door buses invite comparison as a result of significantly different approaches to delivering the 3-door bus design. It is evident that ST Engineering’s offering – relying on a modification of the existing MAN A95 chassis – resulted in a cumbersome design for passengers using the third door.

On the other hand, the ADL offering is significantly better for passenger flow, with the full-low-floor aisle and rearward positioning of the rear staircase making it ideal for passenger movement.

Assembly in China

The 3 door ADL Enviro500 buses are built in Zhuhai (China), by a collaboration between Alexander Dennis Limited and Zhuhai Guangtong Vehicle Manufacture Co., Ltd.

ADL had partnered with the Zhuhai-based manufacturer since 2011 for bus bodywork manufacturing and assembly, supplying completely-built-up ADL buses to the Asia Pacific region. The largest market for these buses is in nearby Hong Kong, where thousands of ADL buses are operated on public bus routes. In 2019, this partnership was expanded to include chassis manufacturing and assembly, thus unifying most manufacturing and assembly work in Zhuhai.

The 11th character of the VIN number is a plant code, used to indicate the manufacturing facility at which the bus’ chassis was built. On ADL Enviro500 (3-door) buses, the digit is ‘C‘, presumably indicating China. Most 12m Enviro500 buses in Singapore mostly have ‘M‘ for Malaysia, a legacy of ADL’s former chassis manufacturing operations in Pasir Gudang, Malaysia (in partnership with Sime Darby TMA Sdn Bhd). SMB5001A and SMB5002Y carry ‘G‘ for Guildford (UK), where ADL’s chassis manufacturing operations were formerly based.

All Enviro500 buses in Singapore (except for SMB5001A) were assembled in Zhuhai.

Prototype Bus K509

Prior to building the 50 Enviro500 buses for Singapore, a pre-production unit 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).

Main Article: Alexander Dennis Enviro500 (3 Door): UK prototype bus


Bus Fleet & Deployments

The 50 buses are leased to the following operators:

Operator Registration Date Registration
SBS Transit
(25 units)
21 Sep 2021 SG6338A
8 Oct 2021 SG6344G & SG6347Z
25 Oct 2021 SG6337C & SG6351K
11 Nov 2021 SG6342L, SG6354C, SG6356Y & SG6358S
23 Nov 2021 SG6339Y, SG6343J, SG6352H, SG6353E & SG6361G
2 Dec 2021 SG6334K, SG6359P, SG6362D – SG6364Z
13 Dec 2021 SG6333M, SG6355A, SG6360J & SG6365X
31 Dec 2021 SG6335H & SG6348X
SMRT Buses
(5 units)
21 Sep 2021 SG6349T
8 Oct 2021 SG6345D & SG6350M
25 Oct 2021 SG6340S & SG6346B
Tower Transit
(20 units)
2 Dec 2021 SG6341P
13 Dec 2021 SG6357U
22 Dec 2021 SG6366T – SG6372A
30 Dec 2021 SG6336E, SG6373Y – SG6376P & SG6378J
21 Jan 2022 SG6377L, SG6379G – SG6382X

Revenue service with both SBS Transit and SMRT Buses commenced on 26 October 2021, with the buses deployed on Bus Services 190 & 974. Revenue service with Tower Transit commenced on 30 December 2021, with buses deployed to Bus Services 854 & 854e during the morning peak hours and Service 857 during the evening peak hours.

See Also: Alexander Dennis Enviro500 (3-Door) Bus Launches


The ADL Enviro500 (3 Door) bus styling comes from the 2014 Enviro400 MMC, which was subsequently adopted by the Enviro500MMC Facelift later in 2015. This design features bolder, sharp-edged lines on the headlights and taillights.

Buses are painted in LTA’s unified Lush Green base livery, with accompanying SGBUS decals. The rear of the bus is primarily black, outlining the upper-deck window edges as well as the engine and air-conditioning unit.

As compared to the earlier ADL Enviro500 buses, this batch of buses has the rear overhang extended to accommodate a new third door. A single-leaf door is installed at the rear of the bus to improve passenger flow inside the bus.

A striking ‘V’-shaped windowline on the offside of the bus catches our attention immediately – a new for Singapore’s public buses. Dubbed glass staircases, this design element has been increasingly incorporated into European-made double-decker buses and has been a standard feature on most new buses in Hong Kong.

However, don’t be tricked by the design element – both staircases are actually rear-facing staircases, and the glass panels do not run for the whole length of the staircase due to privacy concerns (Low window lines have been covered up on the demonstrator 3-Door MAN A95 and 3-Door MAN A22 as well.)

These buses also feature Electronic Display Signs (EDS) and PIDS screens supplied by LECIP, common to most new buses for the Singapore market.

Continued on Page 2 – Full interior coverage & Gallery

  • Lower Deck
  • Upper Deck
  • Staircase
  • Drivers’ Compartment
    • Collision Warning System
    • Anti Fatigue System
  • Features In-Depth
    • Wheelchair Bay
    • PIDS
    • Door systems
    • USB Charging Ports
    • APCS
  • Pre-delivery road tests
  • Pre-delivery visit to Hong Kong and UK
  • Delivery to Singapore
  • Die-cast Bus Model
  • Gallery

47 thoughts on “Alexander Dennis Enviro500 (3 Door)

  • 17 August 2022 at 12:04 AM

    Very stupid deployment in SBST side. Instead of 37 n 107 it would be of better use on services like 60 45 65 89 109 or 147. To name afew.

    • 4 December 2023 at 7:14 PM

      I do agree with you. SBST uses this bus on Service 4, 11,23,28 and 974

    • 5 December 2023 at 1:12 PM

      Sorry for the mistake. I do not agree with you. SBST operates this model on SVC 4, 11, 23, 28, 974

    • 14 December 2023 at 11:57 AM

      haven’t heard of road traffic exemption for 3 door bus

    • 12 May 2024 at 5:12 PM

      Ya la. All priortise to Tampines route more than other side which truely requied it. eg 147, 109, 198, 99 to name a few which has high load as well. 37 , 4, and 69 should remove the 3 doors as it a short route. I can say la. All paster east more than other side. You all never realise meh, east side especially tampines (BNDEP) always get the newer fleets than other.

  • 11 June 2022 at 12:57 PM

    Got several cases overheated..probably the small engine cannot cope with the DD chassis including aircon and torque restriction…LTA should decrease the torque restriction else it will be fuel guzzle and cases of overheating.Modern Euro6 engine exhaust system has too many filters and for our tropical climate waiting to happen only..Bedok North side engine mostly got rattling/metal gazing sound

  • 21 January 2022 at 5:06 PM

    It’s finalised,SBST with 25 buses,TTS with 20 and SMRT with 5 buses.

    • 5 February 2022 at 7:59 AM

      I heard that you were a former bus driver. Do you know why GAS is not getting it?

      • 13 October 2023 at 7:56 PM

        Go Ahead Singapore does not want ADL Enviro Buses as GAS loves MAN Buses

  • 25 November 2021 at 8:22 PM

    I know that SG6339Y, SG6343J, SG6352H, SG6353E & SG6361G have been registered to SBS but the SGWiki website, for some reason, is down for a few days now, leaving the Admin unable to wite down new info on the website.


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