The NZ Transport Agency (NZTA) is undertaking an investigation to assess the options for upgrading the intersection of Russley Road (SH1) and Memorial Avenue. This intersection is strategically important as it is the main access point to the Christchurch International Airport, and is part of the Christchurch Western State Highway Corridor which is a key strategic arterial route.
The intersection is currently controlled by a two lane roundabout. During morning and evening peak periods the intersection is experiencing congestion causing unacceptable delays to traffic. These delays are expected to get worse as traffic volumes on Russley Road and Memorial Avenue increase.
This intersection improvement investigation is part of a wider strategy for improving the Christchurch Western Corridor between Hornby and Belfast. Two adjoining four-laning projects are currently progressing with the Yaldhurst Road to Memorial Avenue section in design phase and the Memorial Avenue to Sawyers Arms Road section out for tender shortly.
Background
An initial scoping report was completed in 2004 which identified a range of options for improvements to the intersection. A copy of this report is included for your reference. The objective of the current project is to identify and investigate improvement options in the interim and long-term, and assess the urgency of the problems at the intersection. The options considered in the scoping report include:
Interim options
1. The addition of left-turn slip lanes on the two-lane roundabout
This option involves installing left-turn slip lanes for traffic turning left from Memorial Avenue East into Russley Road South and from Russley Road South into Memorial Avenue West. However, modelling indicated there would be little benefit gained by installing left-turn slip lanes as the left-turn volumes are a lot smaller than the volume of through traffic. In addition, the right-turn volumes are a lot smaller than the volume of through traffic. It is these movements that cause over-saturation at the roundabout.
2. Traffic signals
This option involves removing the roundabout and installing traffic signals to control the intersection. The intersection has been signalised previously and during this time the intersection had a high crash rate and high accident severity due to the high approach speeds and absence of side friction. Since then the speed limit on Russley Road has been reduced to 80km/h.
3. Three lane roundabout (with left turn slip lanes)
This option involves construction of an additional (third) circulating lane on the outside of the existing two-lane roundabout for traffic heading North and South on Russley Road only. It also involves installing left turn slip lanes on all approaches. This option will increase the capacity of the roundabout; however, this layout has not previously been used in Christchurch and could cause some confusion which may lead to an increase in the crash rate at the intersection.
4. Signalised roundabout
This option involves signalising the roundabout. This option is only considered applicable on very large roundabouts where there is sufficient stacking capacity for the circulating traffic to be stopped and not block the exiting lanes. The existing roundabout is not considered large enough for full signalisation and may need to be two or three times the size for such an option to be considered viable.
Long-term options
5. Grade separation with Memorial Overbridge (structure)
This option involves a full diamond grade separated intersection taking Memorial Avenue over Russley Road with elevated signalised intersections at the two sets of ramps. Given the clearance required over the State highway this option requires significant structures along Memorial Ave towards the City and the Airport, and a significant amount of additional land outside of the existing road corridor.
6. Grade separation with Russley Overbridge (structure)
This option involves Russley Road passing over Memorial Avenue with ramps from Russley Road connecting with the existing roundabout beneath the bridge structure. The Russley Road ramps are essentially at-grade requiring minimal fill. This option requires additional land outside of the existing road corridor.
7. Grade separation with Russley Overbridge (embankments)
This option also involves Russley Road passing over Memorial Avenue with ramps from Russley Road connecting with either the existing roundabout or a signalised intersection located under the bridge structure. It differs from the previous option in that fill embankments are used instead of retaining structures. This option requires more additional land outside the existing road corridor to accommodate the embankments.
Environmental considerations
There are a number of key environmental issues that must be considered in this investigation. The site is a key gateway into Christchurch City from the Airport and as such the urban design aspects of the project are significant. The site is also over the recharge zone for the Christchurch groundwater aquifer system therefore the management and treatment of stormwater when the intersection is being constructed and operating is important.
Making a submission
Submissions closed on 27 February 2009.
Last updated: 12 February 2009
