Saving time at Silverstream signals


25 seconds is quite a long time when you’re in a hurry. It’s enough time for Usain Bolt to cover 200 metres with five seconds to spare. It’s enough time for a hummingbird to flap its wings more than a thousand times. And just try holding your breath for that long.

And it’s not thanks to some big new roading project, but rather some clever tweaks to the traffic signal phasing.

 The NZ Transport Agency’s Wellington traffic operations centre (WTOC) has altered the Silverstream lights to make travellers’ journeys smoother. 

WTOC Project Director Mike Seabourne says the team noticed commuters were sitting in traffic queues at the Silverstream intersection, waiting to turn right into Fergusson Drive, so they made a change. 

“We asked the public what they thought about the light changes through a survey that was pushed out through our Wellington social media channels. Generally everyone thought the tweaks to the right-hand turn signal were a good thing, but there were a few other things that were bothering our customers,” Mr Seabourne says. 

“People told us the detectors that sensed a vehicle was present and triggered a green light couldn’t be triggered by mopeds and bicycles, so we’ve adjusted the sensitivity of the detectors. 

“Road users are also switching lanes at the last minute to beat the queues so we’re also getting our safety team to take a look at road signs, lane markings and other things to improve this.” 

Mr Seabourne says public feedback has been a helpful addition to complement the extensive technical work that goes into fine-tuning signal phases.

 “Designing traffic phases is a complex discipline, in which we need to balance a number of factors while getting as many people through as quickly as possible. While phasing is largely determined by modelling and observation, it’s also helpful to be able to see things through the eyes of people who use these intersections frequently.”  

In total, 47 people responded to the survey and much of their feedback has been taken on board. 

*The Wellington traffic operations centre, based in Johnsonville, is where the state highways are monitored 24/7 by operators to keep roads safe. The traffic signals team and travel advisory team are also based there in a control room environment to keep traffic flowing smoothly and commuters up to date with the latest highway information.