Design roads for heavy vehicles: Austroads


A greater proportion of heavy vehicles and longer “gap acceptance” times mean road designers should shift their focus away from passenger cars

Design roads for heavy vehicles: Austroads
Austroads make recommendations for road design.

 

Austroads has completed a four-year research project investigating the impact of more heavy vehicles on the national road network.

It has found Australia’s growing heavy vehicle fleet is changing the basic requirements of road design.

The project report, Road Design for Heavy Vehicles, analyses data on heavy vehicle crashes from around Australia and New Zealand.

It also undertook its own direct field research to analyse the gap acceptance times – the amount of time and space required for a vehicle to turn through oncoming traffic – for heavy vehicles manoeuvring through a range of intersection types.

Among its recommendations is a call for road designers to focus more on heavy vehicles than passenger cars.  

Wider lanes on some arterials roads, for example, will help longer vehicles navigate turns.

"Where triple or larger road trains are expected designers should consider wider lanes," the report advises.

"Lanes may also need to be widened on curves to allow [the] additional ‘tracking’ required by trucks."

Changes to road alignments and grades could also help make driving smoother and safer for heavy vehicles.

About 20 per cent of casualty crashes involving heavy vehicles occur on crests and grades in rural areas, Austroads’ research found.

Heavy vehicles are also at risk of overheating on particularly steep climbs.

"To overcome the operational and safety problems associated with heavy vehicles driving on an upgrade road, authorities often provide truck climbing lanes," Austroads says.

"On relatively long or steep downgrades, road authorities may provide truck roadside parking strategically located, to allow drivers to stop and check the temperature of the brakes, and if necessary allow them to cool."

Likewise, road shoulders are found to be an important consideration on rural roads.

Degraded shoulder conditions, such as excess loose material or steep edge drop-offs, can lead to greater crash risks for heavy vehicles.

But Austroads says there is a limit to how much back-up bitumen road designers can provide.

"While shoulder sealing provides a marked improvement in safety, increasing shoulder width to greater than 2.5 metres on two lane roads may increase crash risk as some drivers might treat the shoulder as an additional lane."

Further factors highlighted in the report include pavement surfaces, the availability of rest areas, and speed differentials between traffic on carriageways and accompanying service roads.

The Austroads Road Design Taskforce will now critically review the report and its suggested amendments to the national Guide to Road Design.

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