Interurban multiple unit

Walkers Limited and Downer Rail
Industry	Rail transport manufacturing
Headquarters	Maryborough, Australia
Products	Interurban multiple units (IMU) for Queensland Rail's Citytrain system

The Interurban multiple units (IMU) represent a series of electric multiple units constructed by Walkers Limited and Downer Rail at Maryborough for Queensland Rail's Citytrain system between 1996 and 2011. This fleet consists of three distinct subclasses: the 100 series (units 101–110), the 120 series (units 121–124), and the 160 series (units 161–188).

Design

Designed as long-distance variants of the Suburban Multiple Units, the IMUs incorporate features tailored for extended travel. Inside, they offer larger seating, dedicated luggage storage, and toilets accessible to passengers with mobility impairments. Typically, two sets of three-car IMUs can be coupled together, forming a six-car train.

100 series

In preparation for the new Gold Coast line extension to Helensvale, Queensland Rail commissioned Walkers Limited in Maryborough in 1993 to produce four units of the 100 class. These initial IMU100s (numbers 101–104), built in collaboration with ABB, commenced operation in 1996 ahead of the line's official opening. To accommodate rising passenger demand, an additional six units were ordered in 1995 and delivered by 1997. These trains are equipped with luggage racks, accessible toilets for disabled passengers, and high-backed upholstered seats.

120 series

Four units of the 120 series were procured in 1999 specifically for service on the Airtrain line to Brisbane Airport. Entering revenue service in 2001, these trains feature high-backed seats with headrests, a single toilet per unit, and redesigned luggage compartments. Although initially compatible with the 100 series—often operating together as six-car formations—differences in their electrical and mechanical systems have since restricted joint operations.

The 120 series represents the last batch produced by Walkers Limited before its incorporation into the Downer Group at Maryborough. This production was carried out in partnership with Adtranz, which was later acquired by Bombardier Transportation.

160 series

To increase capacity concurrent with upgrades on the Gold Coast line, Queensland Rail placed an order in 2004 for sixteen units of the 160 series. These trains were manufactured by Downer Rail in collaboration with Bombardier Transportation. Their design shares similarities with the Transperth B-series train, V/Line VLocity, and Adelaide Metro 4000 class fleets but includes altered headlight configurations to maintain consistency within the Citytrain fleet. The IMU160s are interoperable with the 260 series Suburban Multiple Units due to comparable technical specifications.

In early 2007, inspections revealed that air-conditioning units on these trains protruded beyond the loading gauge by approximately 10 millimetres. The first IMU160 entered service on 28 May 2007 along the Gold Coast line.

On 31 January 2013, unit IMU173 was involved in a derailment at Cleveland station, resulting in a collision with a station toilet block and causing minor injuries to fourteen passengers. The damaged carriage underwent repairs before re-entering service.

Refurbishment

Starting in the financial year 2023–2024, a comprehensive refurbishment program for the IMU160 fleet commenced. To date, eight units have been upgraded with new vinyl flooring, improved Wi-Fi connectivity, and modified driver B carriages featuring predominantly sideways-oriented seating arrangements.

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