FRANK BEETON gives us the lowdown on some low-height, double-deck buses
The overall height of double-deck buses is an important factor in determining where they can be operated. In South Africa, their maximum height limitation is 4,64 m, whereas most other road vehicles, together with their payloads, may not exceed 4,3 m. This means that operators need to carefully plan routes for double-deck buses, so that they do not fall foul of low bridges, or clash with street furniture and overhead wires.
In the late 1920s, British bus manufacturers started developing “low-bridge” double-deck designs to allow wider use of the type in areas where historically low railway bridges or overpasses were encountered.
These designs used offset gangways and four-abreast seating on the upper deck to lower the roof height. This concept was developed further in the 1950s with drop-centre rear drive axles; allowing the lower saloon height to be reduced.
However, the limitations imposed by the contemporary use of conventional “body-on-frame” designs placed practical limits on the amount of height reduction possible.
Subsequently, double-deck buses fell from widespread favour, and most urban transport networks adopted long single-deck and articulated buses to carry heavy passenger loads, although these configurations inevitably obliged many of the passengers to travel standing.
Recent efforts to restore the popularity of public transport usage have turned the spotlight back on increased provision of seating accommodation. This has prompted bus manufacturers to refocus attention on reducing double-deck bus height.
A year ago, British bus specialist Alexander Dennis Limited (ADL) added a 100-passenger, 4,1-m high version of its Enviro500 double-decker to its catalogue, which already included 4,27 and 4,17-m versions. The reason for this was to gain increased access to the American and Canadian markets without requiring buyers to apply for over-height permits.
Instant market acceptance showed that ADL had opened up an important new market niche. The company has since moved on to develop an even lower, 83-passenger, 3,9-m high, three-axle variant for Go Transit in Toronto. This model, designated SuperLo E500, offers the same upper-deck interior height as its 4,1-m sibling and incorporates a large secure luggage compartment on the lower deck.
The further reduction in overall height has been achieved by reducing the chassis profile by 75 mm, and strengthening the frame. This is claimed to have lowered and flattened the floor, and reduced entrance step heights.
The technical specification of the 12,9-m long Enviro500 includes a Cummins ISL9 turbocharged and intercooled six-cylinder diesel engine with EPA 2013 compliance, which develops 246 kW or 285 kW (330 or 380 hp). It features Allison B500R, Voith D854.6 W53, or ZF 6AP1700B six-speed automatic transmissions, an integral retarder as well as full air suspension.
The low height is obtained by using a deep drop-beam front axle, drop-centre rear axle and deep drop-beam steering rear trailing axle. GVM rating is 26 500 kg, and the vehicle has an overall width of 2 520 mm.
Production of SuperLo model has commenced at ADL’s Guildford facility, and preparations are under way for contract assembly of all three E500 versions in Vaughan, Canada. Customer deliveries are scheduled to commence during the third quarter of 2016.
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