In April 2019, the Land Transport Authority purchased a batch of 100 new double-deck buses with three doors and two staircases. This batch comprised 50 MAN A95 buses and 50 ADL Enviro500 buses.
The idea of a 3-door, 2-staircase double-decker is to promote passenger flow on services with regular boarding and alighting. On existing two-door buses, a common bottleneck is caused by alighting passengers from the rear of the bus clashing with boarding passengers making their way into the bus – a problem we do see on our ISBs as well. This problem is exacerbated with double-deck buses, as the staircase is the bottleneck between passengers descending and passengers boarding. The entire upper deck must disembark before boarding passengers can move into the bus.
3-door 2-staircase double-deckers aim to resolve this problem by providing a second staircase and a third door at the rear. The objective is separating boarding/ascending passengers from alighting/descending passengers. This improves passenger flow, reduces dwell time, and encourages better utilisation of the upper deck as passengers may be increasingly likely to use it on shorter journeys knowing they can disembark with ease.
London’s New Routemasters
3-door buses are increasingly common in left-hand-drive (LHD) markets, but not as common in right-hand-drive (RHD) markets like the UK and Singapore. Many bus models are designed to support three doors on the right of the bus – this includes the Volvo B9L fleet used in the ISB, which has the engine block and drivetrain designed to take up only the left half of the rear, leaving room for a right-side door. As the market for 3-door RHD buses is smaller, there have not been many models produced whether in single or double deck configuration.
One such bus model was designed by Wrightbus for London in 2012. This model combined the rear staircase layout of the original Routemaster (ie the famous “London Bus”) and the front staircase of typical modern double-decker buses, to create a 3-door 2-staircase double-deck bus where the engine was on the right of the rear. This bus was named the “New Routemaster”, and was designed specifically for London.
The front staircase of the New Routemaster is in the regular position behind the driver, while the rear staircase is located at the rear end of the bus and leads directly to the open rear platform of the bus.
As the bus is not air-conditioned, there is less equipment that needs to be squeezed into the bus. The rear staircase offers a view out of the rear as seen below.
The New Routemaster, unfortunately, was not very well-received. The concept of the New Routemaster called for boarding and alighting at any door, but with the phaseout of conductors due to high costs, the bus was reverted to front-door only boarding (as is the case on other buses, and in Singapore) to prevent fare evasion. The bus was also plagued with other design issues such as poor ventilation and unreliable hybrid technology. Transport for London has since abandoned all future plans to purchase New Routemasters, and switched back to conventional double-deckers with one staircase and two doors.
Singapore has also been keen on the concept of 3-door double-decker buses. Since 2017, a 3-door bus registered SG5999Z has been operating on Singapore roads. This demonstrator started life as a MAN A95-based concept bus displayed at a 2016 LTA bus carnival, with many special features such as headrests and USB charging ports.
Unlike the other concept bus at the carnival (an ADL bus), it was developed as a functional MAN A95 with an engine, so only minor modifications were needed to put the bus into service as a trial. The bus was extended from 12m to 12.8m by welding a new section into the chassis, and a second staircase was fitted.
Passengers would ascend from the normal staircase on the right (offside) of the bus, and descend from a second, front-facing staircase on the left (nearside) which led to a “third” door. From the outside, it was not immediately obvious that SG5999Z had 3 doors as the second and third doors were adjacent to each other in the middle of the bus.
The bus generated enough positive feedback for LTA to consider further purchase of 3-door buses. However, two features of SG5999Z were deemed inappropriate: the second staircase, being forward-facing, was judged unsafe as passengers could fall down the stairs if the bus were to brake abruptly. Furthermore, the length of the bus was prohibitively long and impacted the turning radius.
There was also a 3-door single-deck MAN A22 concept bus, SG4002G, showcased around the same time, but this one met with little fanfare and was eventually converted to a static display prototype for “smart bus” ideas.
The third door was located after the rear axle, and was a single leaf door. As the engine was located at the lower rear of the bus, the bus had a raised floor after the exit door to accommodate the engine components.
As such, exiting via the third door required passengers to descend from a few steps.
Nobody seemed that interested in the bus, and I did not have time to catch it when it was on service to get better interior photos, so you can check out Land Transport Guru’s writeup here.
The other concept bus from the carnival was built on an ADL Enviro500 chassis without an engine and never entered service. A writeup on it can be found here; its interior layout is identical to the production 3-door Enviro500s that I cover later.
The final tender called by LTA required 100 buses, compliant to Euro 6 specifications. The buses were to have two staircases, one entrance, and two exits, with the second exit being a single-leaf door located behind the rear axle unlike SG5999Z. To address the length concern, the buses were capped at a length of 12.5m. In the end, 100 buses ordered were split across the two manufacturers who provided concept buses for the carnival.
MAN (through ST Kinetics) supplied fifty 3-door A95 buses with facelifted Gemilang bodywork.
Alexander Dennis Limited (ADL) supplied fifty 3-door Enviro500 buses with facelifted ADL bodywork.
For the sake of my sanity and everyone reading this, I will refer to the three doors as the front, the middle and the rear. The middle door is the dual-leaf door in the middle of the bus, and in the same position as the exit door on 2-door buses.
The production 3-door variant of the MAN A95 double-deck bus was first introduced in early 2021. Registration and delivery was carried out alongside the normal 2-door variant of the same model. The 3-door variant used the same Gemilang MAN Lion’s City design, so the buses externally resemble their 2-door Euro 6 counterparts. Unlike the 2-door MANs, they use a newer seat design – the Vogel Century which is more rounded.
3-door MAN A95s can carry 123 people, while Euro 6 2-door A95s can carry 139.
For this model, MAN and GML took the existing A95 chassis and modified it for a 3-door design by fitting a second staircase near the rear. No engine or drivetrain components were relocated. The second staircase resembles the first staircase and is also rear-facing, but is positioned over the rear right wheels instead of the front right wheels. Passengers who disembark from the rear staircase will end up in between the middle and rear door.
As the rear door swings out to the rear of the bus, the rear overhang is quite long – note how the passenger compartment extends beyond the door.
I would say the second staircase is well-utilised, but not the rear door. The second staircase was rather visually prominent to passengers as it is near to the first, and I observed many people head to the rear to descend via the second staircase. This is good, and promotes passenger flow through the bus via the upper deck.
The visual prominence of the second staircase also applies to the lower deck – see Land Transport Guru’s photo below, where the “bulkhead” formed by the second staircase is immediately visible.
As minimal modifications were made to the chassis, the rear section of the chassis still features a raised platform around the last row of seats as per normal. As such, the rear door is not low-entry (or should that be low-exit?) as passengers must go up one step to reach the platform and then down two steps to exit the bus. This makes usage of the third door rather awkward.
On my rides, I did not observe any passengers choosing to use the rear door, with the sole exception of the few seats located near it (that were on the raised platform). All the passengers who descended from the rear staircase turned right towards the middle of the bus, and alighted from the middle door.
The third door also opened out towards the rear of the bus, and was prone to striking the heads of passengers. Additional retrofits were needed after the buses entered service, notably stickers reminding passengers to wait, and foam cushioning on the door arms (which didn’t stop my friend from getting bonked on the head).
The location of the raised platform also necessitated modifications to the rear of the upper deck; passengers on the platform downstairs would need some headroom so a section of the upper deck needed to be raised. This resulted in an awkward seating layout at the rear of the upper deck, where the section above the rear door is blocked off and replaced with side-facing and rear-facing seats.
Admittedly, there is some novelty to taking the side-facing seats with a panoramic view outside the rear side windows. Overall, however, it feels like a lot of effort to redesign the body around the chassis, with mixed results.
The 3-door variant of the ADL Enviro500 only appeared on Singapore roads much later in 2021. Like its two-door cousins, this model was assembled in Zhuhai using ADL’s own bodywork, but with a facelifted design that distinguishes it from the 2-door Enviro500s which had all been delivered years earlier. The seats in the 3-door E500 are the familiar, more blocky Vogel System 750 which has been used in buses for many years.
3-door ADL Enviro500s can carry 132 people, while 2-door Enviro500s can carry 134.
This chassis was designed specially for 3-door use in Singapore. 3-door Enviro500s exist in Europe but are designed for the LHD environment there. The Singapore buses feature a redesigned engine compartment to facilitate the third door on the left, by flushing the engine and drivetrain components to the right.
Unlike all other Enviro500s and A95s, the powered and unpowered axles were swapped in position, presumably to make engineering easier by bringing the powered axle closer to the transverse engine. The rearmost axle is powered, and the middle axle is an unpowered pusher and can steer to reduce scrubbing. This axle setup was last seen in the common Volvo B9TL, although middle-axle steering has not been seen in Singapore since the Volvo Olympian.
With the redesign, the lower-deck floor is low all the way to the rear. The second staircase is located at the extreme rear and connects directly to the rear door. It is still rear-facing despite what the windowline may suggest, but it is more “curled” (more sideways steps) and positioned further back, such that the landing of the stairs is right at the rear door. This means that the staircase layout is exactly that of the New Routemaster.
This makes the rear door much more passenger-friendly – no steps need to be climbed in order to access it. Exiting via the third door is simple for both upstairs and downstairs passengers.
The rear door of the Enviro500 swings towards the front of the bus instead of the rear, which is better for the curvature of the bus stops. Interestingly, the two card readers are mounted on the same side.
The rear section of the bus is very slightly raised, but still counts as a fully low floor as it simply slopes up and down, with no steps.
However, it must be noted that due to the second staircase being at the extreme rear of the bus, it is not as visible to passengers as the second staircase of the MAN A95. In contrast to the MAN which had an approximately 50-50 split in terms of descending passengers, only about 40% of alighting passengers chose to descend the rear staircase.
In general, the ADL Enviro500 seems to be a better design, though a more expensive one with less parts commonality with existing buses.
Overall, between the two production models, the 3-door ADL Enviro500 gets the nod from me. Maybe it’s the more user-friendly design that makes the best use of the new specifications, or just the fact that it looks like more thought and engineering went into the model. Ironically, the ADL Enviro500 was developed ground-up for Singapore at considerable expense, but legally there cannot be any follow-up orders – LTA has announced that all future bus purchases will be either hybrid or electric. To that end, I think ADL has shrewdly demonstrated their product in Hong Kong, another possible market for the RHD 3-door bus, so all the best to them.
Despite being longer, due to the space required for doors, staircases and equipment, the 3-door buses have fewer seats and lower capacity. A bit of passenger capacity is thus sacrificed for better flow. As earlier computed, the 3-door MAN A95 buses can take 16 fewer than their closest 2-door counterparts while the 3-door Enviro500s take only 2 fewer passengers than their 2-door cousins. This is another reason why I admire the Enviro500 design more.
With electric buses, though, new potential is unlocked. As electric motors are structured differently from diesel engines, new drivetrain possibilities hopefully means new ways to integrate a third door at the rear of a RHD bus without requiring a raised platform.
Currently, the Linkker LM312 and CRRC TEG6125BEV03 already demonstrate that a low-floor 3-door electric bus design is possible. I have reviewed the design of the 3-door single-deck buses here. Meanwhile, the Yutong E12DD, an electric conventional 2-door double decker bus, places the batteries behind the rear wheels, so the passenger compartment ends around the wheels and a third door is not feasible, but battery placement appears to be flexible so there may still be possibilities yet.
With the recent announcement that the next generation of NUS ISBs will be electric, this does open up possibilities for us to improve passenger flow as well. Before the pandemic, I did wonder if 3-door buses would improve boarding and alighting because people typically boarded from both doors. As a result, passengers in the rear of the B9Ls found it difficult to exit as passengers were boarding from the middle door which became a huge bottleneck.
A third door would distribute boarding and alighting throughout the bus. Now that there are ID checks on ISBs, however, boarding is only done at the front door – which means, like public buses, the other two doors can be used for exiting to speed up dwell time.
Interesting times ahead, certainly!
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