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North-Western Motorway

Across the road network there are some locations which we have received high numbers of feedback and comments for. These usually ask why are ramp signals turned on when the motorway appears to be free flowing or that getting onto the motorway is very slow and the onramp and arterial road is congested.  

1. Royal Road On-ramp city bound

The on-ramp signals at Royal Road form part of a co-ordinated group of ramp signals. The Hobsonville Road / Royal Road / Lincoln Road ramp signals have been configured so that the motorway traffic flows can be maintained for as long as possible before congestion starts during the morning peak.  The metering rates at Lincoln Road, Royal Road and Hobsonville Road have been decreased in relation to the demand on the network.  Drivers are advised that we observe congestion between 6:20am and 8am.

A project to provide extra lane capacity is being undertaken by NZ Transport Agency as part of the Western Ring Route improvements. 

Visit the SH16 Lincoln Road Interchange project (external link)  to find out more

2. Te Atatu Road Onramp

An example typical question about the Te Atatu onramps: Traffic congestion is very bad in residential streets. At 7am, I sit in traffic for 20mins before I can get on to the main road and then 30mins to get on to the motorway.  Overall, a trip to the Shore that should take me 20mins now takes me an hour.  I am becoming resentful of residential streets being clogged by non-residents seeking ways to avoid traffic on Te Atatu Road.

Our data suggests that the traffic delays are similar to those before ramp signals were installed. 

The main constraints are:

  1. The northbound traffic from Te Atatu and the southbound traffic from Te Atatu peninsula competewith each other and with traffic already on the motorway from other upstream ramps to get onto the motorway city bound where the motorway may already be congested.
  2. The city bound ramp signals try to manage the total number of vehicles entering the motorway at this location. The motorway capacity down stream of this interchange has a finite maximum. The ramp signals try to manage this inflow so that the traffic further down the motorway does not come to a total stand still, in turn the city bound traffic flow can be maintained improving overall journey reliability.  Managing these ramp signals and the demands to enter the motorway also helps those motorway users who are entering the system through other upstream on ramps such as Lincoln Rd.

The motorway capacity will increase with the SH16 upgrade project which is underwayas a part of the Western Ring Road project. The project will provide an additional lane city bound along the motorway. There will be added improvements at the Te Atatu Rd interchange.

Visit the SH16 Te Atatu Road Interchange project (external link)  to find out more.

3. Waterview and Western Springs Onramps

The metering rate automatically changes according to multiple factors such as the on-ramp traffic volume, queues on the ramp, motorway lane configuration and motorway congestion. The on-ramp at Western Springs is a lane gain which means that it does not have to merge with existing motorway traffic. It gains an extra lane on a flat section of motorway helping overall traffic speed. So this section of motorway has more capacity and ability to move more traffic than compared to say the Great North Road on-ramp at Waterview. By contrast, the Waterview on-ramp has to merge with the motorway where it has a ramp signal priority lane which merges with the ramp signal traffic and merges on an uphill section of motorway. The volume of traffic at Western Springs is also higher than the Waterview on-ramp.  This in turn means that the ramp signals at Western Springs has a slightly lower red time on average at the signal because of the ramp signal queue management functionality.

Both on-ramps are working as a co-ordinated group to mitigate the flow breakdown prior to the Central Motorway Junction. Thus there are times when ramp signals at the Waterview on-ramp are on and no congestion is observed until the Western Springs interchange or closer to the SH16 to SH1 southbound link. The flow breakdown congestion around the Carrington Road over-bridge on the motorway also often restricts the on-ramp traffic from the Waterview on-ramp during the morning peak causing extra delays at this on-ramp.

Visit the Waterview project (external link)  to find out more.

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