4 lane roads, when to

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Frequently Asked Questions – 2008 Transit NZ – SH1 Cambridge-bypass web page.

7. Why are you only building two lanes?

Two lanes will be adequate for some time, according to modelling of traffic flows. So Transit is planning an initial two-lane highway with the possibility of some passing lanes. Provision is being made to expand this into a four-lane highway as future traffic demand requires.

The same question is asked in this article Wairere-Drive-laning-dilemma from the Waikato Times 01 Jun 2014,

Here the question is answered by the city infrastructure general manager:

Traffic models indicated two lanes would work well up to 2021 plus

The city infrastructure general manager also references historical development:

The reason why the ring road narrowed to two lanes lies in the historical development of the project.

The historical aspect referred to is the 2006 Notice of Requirement–Hamilton Eastern Arterial (HEA)–Appendix 6, page 12, where we get some predicted traffic volumes.

Hamilton Eastern Arterial-Appendix 6 page 12 copy


This discussion on when to add extra motor vehicle lanes or roads goes on as we see in –Proposed Ruakura development plan change draft decision and Report – page 245

13. Transport: The impact of the increased volumes of traffic on the network Capacity of local roads

[878] Ms W advised that a single lane road in each direction could carry between 18,000 and 20,000 vpd, and that a two-lane road in each direction could carry between 35,000 and 40,000 vpd. We were also informed that it is not uncommon for collector roads such as Silverdale Road to carry 7 to 10 % heavy commercial vehicles and for arterial roads such as Wairere Drive to carry up to 12 to 15 % heavy commercial vehicles. Accordingly, a road carrying 10,000 vpd total would normally be expected to be able to carry 700 to 1,000 hvpd. A road carrying 15,000 vpd total would normally be expected to carry between 1,000 and 1,500 hvpd. A collector road carrying 20,000 vpd total would normally be expected to be able to carry between 1,400 and 2,000 hvpd. An arterial road carrying 20,000vpd total would be expected to carry between 2,000 and 3,000 hvpd.

The Transportation Modelling Report for the Board of Inquiry – Ruakura Development Plan states some limits to trigger changes to transport infrastructure.

This trigger would measure link volume on Ruakura Road (East of Wairere Drive) and Wairere Drive (south of Ruakura Road) since these are the most critical network components. Other intersections within the area of influence of the Plan Change, including the signals at Ruakura Road/Knighton Road and Ruakura Road/Silverdale Road have adequate capacity.

Development in any or all of these three areas could proceed subject to the trigger which has been set at the upper limit of LOS D. This is assessed as 1,200 vehicles per hour (vph) (one‐way) for Ruakura Road and 1,400 vph (one‐way) for Wairere Drive during the weekday morning or evening peak period.

For further development to proceed once the trigger is reached, the Spine Road is required to connect the Fifth Avenue extension to Ruakura Road. A road with one lane in each direction is adequate to meet forecast demands at 2041.

Going back to the Frequently Asked Questions – Why are you only building two lanes?The Cambridge bypass predicted traffic flow for 2021 is about 12,600 vehicles per day or 6,300 vehicles per day per each direction. I am suggesting a possible 840 vehicles per hour per lane at peak periods using the rule of thumb from this earlier post – number-of-cars-per-lane

And last from Access Hamilton network action plan – 2010 – page34

7.6 Timing of 4-laning

… Wairere Drive has shown that this two lane carriageway can accommodate traffic volumes up to 26,300vpd (2008 traffic volume) before 4-lanes are affordable and effective.

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