Memorial Ave Intersection

The 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 State highway 1 and Memorial Avenue increase as predicted. An initial scoping report was completed in 2004 which identified a range of interim and ultimate options for improvements to the intersection. The current project proposes to

Interim Options

1. Left-turn Slip Lanes on 2-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 signalising the intersection. The intersection has been signalised in the past 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.
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. This option requires 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 the existing roundabout 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.