Questions to WA State Government

Thank you to our WA State Government for answering WA Transport Magazine reader’s questions. If you have a question that is related to the transport industry please email it to the publisher at: karen@angrychicken.com.au

Question:

Why do MRWA when building new passing lanes insist on starting them half way up a hill instead of 500 metres or more prior … thus making it easier for ‘all’ to pass slower vehicles safely? The way they are designed everyone loses their speed by the time you get to the passing lane (trucks I mean).

Answer from Main Roads Spokesperson:

Main Roads’ determination of passing lane locations is based on Part 3 of the Austroads Guide to Road Design and Section 9 of the agency’s supplemental policies on the Guide, this can be found at www.mainroads. wa.gov.au/BuildingRoads/StandardsTechnical/ RoadandTrafficEngineering/Pages/home.aspx

Considerations when selecting a passing lane location are the warrant for its construction (based on average annual daily traffic volumes) and the geometric requirements for vehicles to safely diverge from and merge back with the main carriageway.

It is important that drivers have good visibility both to diverge at the start of the overtaking lane and, in particular, to merge at the end of the overtaking lane. If the overtaking lane is located in a sag curve

It is important that drivers have good visibility both to diverge at the start of the overtaking lane and, in particular, to merge at the end of the overtaking lane

(vertical curve between a downhill and uphill sections of road) there will usually be good sight distance to the diverge if it is located on the uphill side of the vertical curve.

Besides visibility, another reason why the passing lane is located on the uphill section is because if it was located on the downhill section (or close to the downhill section), all vehicles would be travelling at the speed limit and so there would be limited opportunities to pass anyway. There is more value in locating the passing lane where some vehicles have started to slow down.

If drivers have questions regarding the design considerations for passing lanes in a specific location, they are encouraged to contact Main Roads on 138 138 or via enquiries@mainroads.wa.gov.au

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