Open-Top Tour Bus

Overview

An open-top tour bus is a double-decker road vehicle built for city sightseeing rather than scheduled service. The defining feature is the upper deck, which has no roof, so passengers on top get an unobstructed view of buildings and landmarks. The enclosed lower saloon carries passengers who prefer shelter, along with the driver, the wheelchair bay, and the entrance. Two staircases connect the decks so that boarding and alighting flow does not back up at a single point.

Most operators run these buses on fixed sightseeing loops with hop-on hop-off ticketing. A typical vehicle is 11.0-11.5 m long, 2.55 m wide, and seats 52-58 passengers split roughly 30 on top and 22 below. The base vehicle is a standard double-deck bus chassis; the conversion removes the upper roof, adds rollover protection, and fits weather-resistant fittings throughout the open deck.

Powertrain and driveline

Propulsion comes from a rear-mounted diesel engine, an inline-6 turbo diesel of about 7 litres producing 220-250 kW and certified to Euro VI. The variable-geometry turbocharger keeps boost available at the low engine speeds that dominate sightseeing duty, and the cooling pack is sized to reject full heat load while the bus creeps in traffic. Emissions control uses a particulate filter and an SCR catalyst fed by the AdBlue dosing module.

The engine drives a 6-speed torque-converter automatic with an integrated retarder, chosen because stop-start city running would wear a manual clutch quickly. Torque passes through the propeller shaft to a hub-reduction rear axle. The hub reduction lets the axle line sit high enough for ground clearance while still giving the gear ratio a heavy double-decker needs. Steering uses a front steer axle with a hydraulic steering box. Inside the gearbox, planetary gear sets supported on bearings and sealed by oil seals provide the six ratios, all carried in a cast aluminium case.

Body structure and rollover protection

Because the upper deck has no roof, the body cannot rely on a roof skin to tie the two side walls together. The body structure handles this with strengthened rollover hoops and a stiffened inter-deck floor that works as a structural diaphragm. The underframe and welded side frames carry the load path down to the axles, and the exterior is closed with body skin panels. The lower deck keeps a bonded laminated windscreen at the driving position. Rollover strength must be demonstrated even with the roof removed, which is why the hoops use high-strength tube.

Open upper deck and weather features

The open deck is designed for permanent exposure to sun and rain. Seats use a drainable polypropylene shell with a UV-stable finish, and the floor slopes to drainage channels and scuppers so water does not pool. A perimeter guard rail of laminated glass panels held by stainless posts contains passengers at the edge, while a front wind deflector cuts the wind blast on the leading rows. Grab poles give handholds, and sealed LED strips in the deck lighting handle evening tours. Each staircase has anti-slip treads, stainless handrails, and a self-closing stair gate at the top so passengers do not climb while the bus is moving.

Audio commentary system

The audio tour system gives commentary in several languages. A head-end unit holds recorded tracks in solid-state storage and uses a GPS module to play the right segment as the bus reaches each landmark. Passengers plug a headset into a seat audio unit and pick a language with the channel selector. An amplifier drives the seat bus and the driver PA speakers for live announcements. The electronics use a controller board, an audio processor, and an operator display.

Materials and supporting systems

Outdoor fittings favour stainless steel, marine-grade aluminium, and UV-stable plastics so the open deck survives years of weather. Braking is full-air and dual-circuit: an air compressor charges reservoirs that feed air disc brakes, with an EBS module running ABS and a retarder for downhill control. The electrical system runs at 24 V from an alternator and twin batteries through a fuse and relay box. Climate control is fitted to the enclosed deck only: the lower deck HVAC uses an AC compressor, a roof condenser, an evaporator, and a heater core, since the open upper deck cannot be conditioned.

Variants and use

Operators specify the build for their climate and route. Warm-city fleets often delete the upper-deck wind deflector and add more drainage, while cooler-city fleets keep the deflector and sometimes fit a removable canopy over part of the deck for shoulder-season running. Route length sets the fuel tank size and whether a battery-electric chassis replaces the diesel powertrain. Service intervals centre on the open-deck fittings, the brake pads, and the audio system headsets, which are replaced frequently because passengers keep or damage them.