Nano Girl Michelle Dickinson: Who to blame for traffic delays?

Auckland traffic seems to be in a permanent 'jamiton'. Photo / 123RF
Auckland traffic seems to be in a permanent 'jamiton'. Photo / 123RF

We've all sat in motorway traffic; crawling along at a snail's pace wondering what the hold-up is. It's especially frustrating when out of nowhere, the road suddenly clears without a clue to suggest what caused the delay.

Mathematicians studying these phantom traffic jams found that when traffic gets heavy we drive closer to the car in front. With this reduced stopping distance, it takes only one driver pushing on the brakes to cause the driver behind to slam on to his or her brakes, thus creating a ripple of breaking through the traffic. This event is referred to mathematically as a "jamiton", from the word "soliton", the scientific term used to describe a self-sustaining wave that maintains its shape while moving.

Wave equations predict a jamiton is most likely to occur when there is a high density of traffic on the road and at areas where traffic merges such as a motorway on-ramp. To try to reduce these factors, on-ramp traffic lights were brought to Auckland's motorway system in 2006.

This week the system got an upgrade, with faster sampling times creating a more powerful and accurate set of data for the operations centre.

Based in a screen-filled office in Takapuna, the joint Transport Agency/Auckland Transport operations centre controls the city's ramp signals, monitoring more than 2500 cameras along our road network.

For the past 10 years, many Aucklanders have cursed those annoying lights that seem to create more delays than they solve. However, the research is clear: intelligent transport systems including on-ramp lights are engineered to reduce your journey time around peak travel hours if you play by the rules.

The ramp signals are fully automated and integrated controlling on-ramps several exits ahead of a detected congested area. They assist in clearing traffic by reducing incoming traffic flow and helping the snarl-up to disperse. This means that sometimes on-ramp lights are activated even though the motorway traffic appears to be free-flowing when you get on.

Auckland's on-ramp signals use an algorithm based on the Sydney Co-ordinated Adaptive Traffic System (SCATS). Inductive loop sensors placed along the motorway, at every on-ramp and on some arterial feeder roads, detect a vehicles presence in each lane.

The lights don't just increase motorway travel speeds and throughput. They have also been shown to reduce crashes at high-risk dangerous merging spots by up to 34 per cent.

Because they take a network approach, ramp signals are designed to have the biggest benefits for those making long journeys. For trips less than three ramp exits long, you may be better off taking a non-motorway route instead.

Many of us still blame the on-ramp lights for the increased congestion on our roads, but it's worth noting that in last 12 months, 47,730 additional cars were registered in Auckland. This rate was higher than the rate of population growth. Too many cars on our fixed capacity road network is a much more likely explanation for the increased congestion.

Additionally, on-ramp red light-runners who ignore the signals are still picked up by the sensors, which immediately compensate with a delayed red light sequence, so increasing congestion - and wait time for those further back in the queue.

With new public transport routes becoming available to us, taking space-efficient car alternative transport options will help the ramp signals to do their job.

So, the next time you call in to say you are "stuck in traffic"; remember you are traffic.

- NZ Herald

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