Imagine controlling a 500-tonne Australian road train with not one diesel engine — but two.

One engine sat in the prime mover. The other was buried more than a hundred feet farther back in the combination, driving its own axle and helping push the trailers through some of Australia's harshest terrain. Later versions of Jim Cooper's extraordinary Co-Ord road trains produced a combined 1,520 horsepower.

This is the forgotten story of Australia's twin-engine road trains, one of the wildest engineering experiments ever to become a genuine working part of the Australian trucking industry.

The story begins with Jim Cooper, a New Zealand diesel mechanic who moved his family to Australia's Northern Territory in 1972. Cooper took over Gulf Transport with just two AEC Mammoth Majors, a Volvo G88 and a handful of worn trailers. Ahead of him lay an 800-kilometre stretch of brutal unsealed road between Alice Springs and Larrimah, where temperatures could exceed 45°C.

As mining and construction expanded during the 1970s, conventional trucks were being pushed beyond their limits. More trailers meant more freight, but also more rolling resistance, greater braking loads, overheating and enormous stress on the driveline. Cooper eventually asked a simple question:

Why did all the horsepower have to come from the front?

In 1978, he commissioned an Adelaide engineering workshop to develop an extraordinary solution — install a second diesel engine on a dolly farther back in the road train. The front truck would pull while the rear power unit contributed drive from deeper within the combination.

Making it work was far more difficult.

Both engines eventually used Allison six-speed automatic transmissions linked through early electronic controls. A single throttle had to coordinate two separate powerplants. If the rear engine pushed too hard or shifted at the wrong moment, the mismatch could damage couplings or potentially jackknife the road train. Engineers even developed a huge 300-litre cooling system for the rear engine to survive Australia's extreme heat.

By 1985, a gigantic six-trailer version powered by two roughly 750-horsepower Cummins engines successfully hauled a 280-tonne payload. Later four-trailer road-going configurations reportedly carried nearly 350 tonnes of payload, with gross combination mass approaching 500 tonnes.

And these weren't merely experimental prototypes.

By 1990, historical records documented 34 twin-engine rigs in active service. They became genuine commercial workhorses hauling enormous quantities of mineral concentrate through Australia's remote interior.

Eventually, technology caught up. By the 2000s, single diesel engines were approaching 700 horsepower, while improved cooling, electronic engine management and stronger drivetrains reduced the need for Cooper's complex twin-powered system. Running two engines also meant additional fuel, maintenance and regulatory costs.

Today, the twin-engine road train belongs to another era — when Australian trucking problems were sometimes solved simply by building something nobody else had dared to try.

Would you have driven one of these 500-tonne monsters through the outback?

Subscribe for more documentaries about Australian road trains, forgotten trucks, outback trucking history and the incredible machines that helped build Australia.

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