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Dynamic lanes’ technical problems mounting up

Posted at 4:13pm Tuesday 30 Jun, 2020

Recent closure of the dynamic lanes for almost two weeks highlighted key challenges with the system, including resilience to heavy use and the quality of the LED lights.

The system, which cost around $3 million, has operated on Whangaparaoa Road, from Hibiscus Coast Highway to Red Beach Road, since January 2018. It uses LEDs and overhead signs to adjust the lanes with peak flow and has reduced congestion along this section of road in the morning and afternoon peak.

According to Auckland Transport (AT) operations planning and performance manager, Chris Martin, a key issue is that the system of LED lights has not proved up to the constant pounding received from traffic.

He says the most recent problem was caused by the pavement moving because of heavy use. This allowed the cable cut into the pavement to be damaged, letting water in that short-circuited the electrical system.

Drivers and nearby residents have noted that, at times, several of the LEDs are not working and some have come unstuck and been found on the side of the road.

“Over the last two years, the supplier has improved the LED canisters, by slight design, materials and installation improvements, and we are now using the new model when we replace the canisters,” Mr Martin says.

He says the reason so many LEDs are in place is that, when some fail, they do not need to be replaced until a whole string has failed.

“This saves time and the cost of shutting down the carriageway.”

The recent cable failure is the third issue since the lanes opened two and a half years ago, and the most serious. It took specialist engineers some time to identify the fault. The contractor spent a number of hours over four nights inspecting and repairing faults in the carriageway, and also investigated the controllers on the side of the road, during the day. A controller was replaced and temporary fixes to the LEDs and cables were carried out, in two zones.

Work on a permanent fix, which requires removing and replacing the cable, is expected to take place this week, during the evening.

Mr Martin says a ballpark estimate of the cost of such repairs is $20,000-$30,000.

Another technical failure, in August last year, saw a section of LEDs incorrectly light up during the morning peak. Mr Martin says the reason for this was identified and corrected to ensure it does not happen again.

A major structural issue, also last August, saw a half gantry fall, narrowly missing a passing car.

Opus has since prepared a report on the gantry for AT which states that the gantry fell because the size and weight of the variable message signs (VMS) on the end of the gantry caused it to vibrate in wind. Over time, this weakened the structure, which cracked and failed where it is welded to the baseplate. Around one-third of the circumference of the pole had cracked before it fell.

“The video footage and failure of one gantry shows that the original gantries supporting the VMS units are particularly wind sensitive to induced vibrations. The gantries are located on a high-volume road and their potential failure poses a significant health and safety risk to vehicles,” the report says.

It recommends that both gantries are replaced with tubular gantries with larger section sizes.

A replacement steel structure is currently being designed and will be installed later this year, Mr Martin says.

The lanes are a trial solution to improve traffic times and, as such, deemed a success. Mr Martin says that AT is currently building another dynamic lane on Redoubt Road in South Auckland.

“We will be trialling LEDs from a different supplier,” he says.

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