Christchurch is somewhat notorious for lacking green arrows compared to other major cities.
Christchurch City Council data shows out of 288 intersections, only 147 have at least one signalised arrow to turn right.
That is slightly more than half.
The city council transport team answered questions from Heathcote Ward city councillor and mayoral candidate Sara Templeton about what is required to install more right-turning arrows.
A report given to Templeton last week highlighted relatively high costs and unintended impacts on traffic flows as factors for consideration when installing more turn signals.
Templeton said it raises more questions for city councillors and the public going forward.
“Apart from cost, it looks like it comes down to whether drivers would be okay waiting a bit longer at lights heading in one direction, to allow others to have a green turning arrow coming from another direction.”
The report states the age, condition and capacity of underground electrical cables makes upgrading intersections with right-turning arrows “very costly”.
The earthquakes caused damage to the cable network, some of which remains today.
The damage limits the capacity of existing cables, while some of the ducts which the cables run through are also still blocked with silt from the earthquakes.
This prevents more cabling from being easily added.
Fixing ducts or re-cabling an intersection to enable right-turning arrows is costly, the report states, with a full intersection upgrade generally about $600,000 and up to $850,000.
A partial upgrade could be about $150,000 to $200,000.
Templeton said she will request an information session between city councillors and staff to discuss the next best options for right-turning arrows.
The installation of green turning arrows is currently being delivered where possible through the city council’s minor safety upgrade programme or the intersection re-cabling programme.
The minor safety upgrade programme is currently over-committed with safety projects, the report states.
To accommodate an increase in the number of right-turn arrows being installed, the city council would have to vote for more budget to the programme.
Installing more turn signals has safety benefits for vehicles turning right, but can also have unexpected impacts on traffic flow, the report states.
Right-turning traffic generally causes vehicles going straight to be stopped for longer.
This reduces the amount of green light time given to lanes going straight, which typically carry the most traffic.
However, sometimes when there is heavy traffic on a right turn, a turning arrow can lead to an improvement in overall delay at the intersection.
Turning arrows may also cause further unintended delays at other intersections due to the co-ordinated timing of the city’s traffic lights and more vehicles being attracted to turning right.
