A right-turn arrow was installed in September last year for traffic turning off Grahams Rd on to Memorial Ave in Burnside. While it reduced delays for right-turning vehicles, it also increased travel times for motorists on Memorial Ave.
Monitoring showed vehicles travelling along Memorial Ave were delayed by an additional 110 seconds at 8am – a 45% increase – and 165 seconds at 3pm, a 67% increase.
By contrast, motorists on Grahams Rd saved about 70 seconds at both peak times.
The findings follow complaints about the new traffic lights at the Harewood, Breens and Gardiners Rds intersection, where there are no right-turn arrows for vehicles entering from Breens or Gardiners Rds.
Christchurch City Council transport staff monitored the Memorial Ave/Grahams Rd intersection as a case study to understand how right-turn arrows affect traffic flow.
The analysis compared stop times recorded in March, before the arrow was installed, with those in November.
The study found that the increase in travel time on Memorial Ave outweighed the time savings on Grahams Rd, resulting in slower overall travel through the intersection.
Traffic volumes at the site are similar on both roads, with an average of 19,320 vehicles per day on Memorial Ave and 18,258 on Grahams Rd.
The city council is considering ways to survey the public for their views on traffic signal operations including green right-turn arrows, and red turn arrows for pedestrian safety.
Traffic signal operations and optimisation were discussed by transport staff and city councillors at a workshop on Tuesday.
A report presented at the workshop described green right-turn arrows as “one of the most common requests from the public” on transport matters.
Christchurch has fewer right-turn arrows than other major cities.
Council data from June last year showed that, of 288 intersections, 147 had at least one signalised right-turn arrow.
Cost is also a factor. A city council report last year estimated adding right-turn arrows could range from $150,000 to $850,000 per intersection, depending on how many arrows were installed and the complexity of recabling.
In some cases, newer equipment such as right-turn arrows cannot be added without renewing the entire traffic signal asset, further increasing costs.
The city council operates a network of about 380 traffic signalised sites across the city
