Bus Rapid Transit Vehicle

Overview

The Bus Rapid Transit Vehicle is an 18 metre articulated bus built for bus rapid transit corridors, where it runs in segregated lanes and stops at raised platforms. It carries about 150 passengers across two rigid sections that pivot around a central Articulation Joint. Most of the interior is standing room with 36 fixed seats, because BRT lines trade seating for throughput and fast boarding. The vehicle uses a diesel-electric series Hybrid Driveline, a low floor at every doorway, and a Docking & Guidance System system that brings the doors to within a few centimetres of the platform edge so passengers step across level.

A BRT vehicle differs from an ordinary city bus in three ways: it is longer and articulated for capacity, it has wide doors on both sides so it can serve kerbside or island platforms, and it carries guidance hardware for precision docking. The structure is split into a Front Body Section over the front and centre axles and a Rear Body Section over the rear axle, with the engine bay at the tail of the rear section.

Hybrid driveline

The vehicle uses a series hybrid layout. The Diesel Engine, a 7 litre Euro VI inline-six, does not drive the wheels directly. It spins a Generator Unit at a near-constant speed in its efficient range, and that electrical output feeds the Traction Inverter, which drives a single Traction Motor of about 240 kW on the centre axle. Running the engine at a steady point and decoupling it from road load is what lets the engine stay clean and fuel-efficient through the stop-start duty of a transit corridor.

A roof-mounted Energy Storage Pack pack using Lithium-Titanate Cell lithium-titanate cells supplies extra current during acceleration away from a stop and absorbs energy when the bus brakes. Lithium-titanate is chosen over higher-density chemistries because it tolerates the high charge and discharge rates of frequent braking and survives many more cycles. The exhaust runs through a SCR Aftertreatment Module module with a Diesel Particulate Filter and an SCR catalyst fed by the AdBlue Dosing Unit unit. High-voltage power is distributed through the HV Junction Box, and the power electronics and engine charge air are cooled by the Power Cooling Pack.

Axles and articulation

The Axle Set has three axles. The front Steer Axle carries the driver's steering inputs. The centre Portal Drive Axle is a portal type: its Differential sits below the axle centreline and a Portal Hub Gear steps the drive back down at each wheel, which keeps the floor flat and low between the wheels. The rear Pusher Axle is a trailing axle that adds load capacity, and its Self-Steer Actuator turns the rear wheels slightly through corners so an 18 metre body can negotiate tight junctions without dragging its tail.

The two sections meet at the Articulation Joint. A Slewing Ring Bearing slewing bearing carries the joint loads while letting the sections rotate relative to each other. A Turntable Bridge Plate forms the rotating floor that passengers walk over, and a flexible Articulation Bellows seals the gap against weather. The Articulation Controller commands two Articulation Damper units to resist sudden swing and prevent jackknifing during hard braking or on slippery surfaces.

Doors, docking, and accessibility

Boarding speed sets the line capacity, so the Door System uses four wide doorways per side. The right side carries six Plug-Sliding Door leaves and the left side carries two Left Platform Door units, so the same vehicle can dock at a kerbside platform or at a central island platform shared by both running directions. Each door has a Door Drive Unit with a Door Edge Safety Sensor to detect obstructions, and all doors are sequenced by the Door Controller. Two Powered Boarding Ramp units fold out for wheelchair access.

The Docking & Guidance System system aligns the doors to the platform. A pair of Guidance Camera units read painted lane markings, four Kerb Distance Sensor ultrasonic sensors measure the distance to the platform face, and a Kerb Guide Roller on each side rides the kerb as a mechanical backstop. The Guidance ECU combines these inputs to keep the door sill gap small enough for level boarding without contact.

Suspension and braking

The Suspension System uses electronically levelled air suspension. Eight Air Spring bellows and eight Shock Absorber dampers ride on air supplied by an Air Compressor and stored in Air Reservoir tanks. At a stop the Level Control Valve units kneel the kerb side down to shrink the step height further.

Braking is handled by the Brake System, an electronically controlled pneumatic setup. Each of the six wheel stations has a Disc Brake Unit with a Spring Brake Chamber that doubles as a spring-applied parking brake. The EBS Module blends friction braking with regenerative braking from the traction motor, so the energy storage pack recovers most of the stopping energy. A Hydrodynamic Retarder adds wear-free deceleration on long downgrades.

Cabin, climate, and electronics

The Passenger Cabin is laid out for high standing density. It has 36 cantilever Passenger Seat units, many Grab Rail stanchions, two Wheelchair Bay positions, and four Ticket Validator readers near the doors. Riders track their journey on Passenger Information Display screens and signal stops with Stop Request Button buttons.

Two Rooftop HVAC Unit climate units form the HVAC System, sized for the heat load of a packed cabin and the air exchange of frequent door openings. The Electrical System runs a 24 volt body network from a DC-DC Converter fed off the high-voltage bus, managed by the Body Controller. The ITS Gateway ties the vehicle into the operator's fleet management, ticketing, and CCTV systems.

Variants and use

BRT vehicles are specified to match each corridor. Operators choose between the diesel-electric hybrid described here, a compressed natural gas engine in the same series layout, or a full battery-electric drive that drops the engine and generator and enlarges the energy storage pack. Door layout varies with platform design: kerbside corridors use right-side doors only, while island-platform corridors need the left-side Left Platform Door units. Some systems run a longer 24 metre double-articulated body with a second articulation joint and a fourth axle. The vehicle is built to run high daily mileage in dense city service, so the Axle Set, Brake System, and door mechanisms are sized for far more stop cycles than a long-distance coach.