The Transition between the Divided and Undivided Road on Australia's Highways

Gaffney, Sara, Bunker, Jonathan M., & Wikman, John (2007) The Transition between the Divided and Undivided Road on Australia's Highways. In Morris, Jenny & Rose, Geoff (Eds.) The 30th Australasian Transport Research Forum, 25 - 27 September 2007, Melbourne.


This paper investigates the transition between a four-lane divided motorway and two-lane highway; a common interface across our national highway network.

The guidelines available, effectiveness of existing treatments and responsibility between state and federal governments are all unclear, contestable topics. In order to achieve some clarity on these issues, the problem first needs to be understood.

The transition was investigated by reviewing the key highway engineering aspects that are traffic operations, highway design and highway management for a divided motorway and a two-lane highway. The outcomes showed that for the most part, existing guidelines and manuals do not provide sufficient guidance on the transition studied in this project.

The reviewed concepts were then applied to a case study of a 15km length of the A1 (Bruce Highway) at Cooroy, Queensland. This study length was segmented into three different classes of road – from south to north: a typical four-lane divided motorway section, a two-lane highway section with standard half-motorway geometry, and a normal two-lane highway section that includes controlled private and local road accesses, and climbing lanes in both directions.

Reviews of the study length segmented by each road class and by direction showed a general trend of abating standards of operation, design and management from the divided road to the undivided road. These results are not aberrant of the different road types, but total crashes across the transition supported the hypothesis that a high design speed environment followed by a constrained environment may lead to the road being ‘overdriven’, thus increasing crash risk.

Some suggestions arising from this case study included reducing the density of potential conflict points in some areas, informing drivers about changing road types, further researching merges onto two-lane highways, and the use of 2+1 roads (such as in Sweden) as an intermediate design solution transitioning from a four-lane motorway to a two-lane highway.

This paper presents the results of these investigations into converging or diverging standards on our highway network.

Impact and interest:

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ID Code: 9899
Item Type: Conference Paper
Refereed: Yes
Additional URLs:
Keywords: rural road, highway, motorway, road design, traffic operation, traffic management, national highway
Subjects: Australian and New Zealand Standard Research Classification > ENGINEERING (090000) > CIVIL ENGINEERING (090500) > Transport Engineering (090507)
Divisions: Past > QUT Faculties & Divisions > Faculty of Built Environment and Engineering
Past > Institutes > Institute for Sustainable Resources
Copyright Owner: Copyright 2007 (Please Consult Author)
Deposited On: 03 Oct 2007 00:00
Last Modified: 29 Feb 2012 13:31

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