News / Calgary

Variable speed limits on Deerfoot could ease congestion: Expert

University of Calgary masters student running simulations that offer answers to traffic problems

Karan Arora uses a traffic simulation software called PTV Vissim to run traffic scenarios along Deerfoot Trail and through the city as part of his masters’ thesis on traffic engineering.

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Karan Arora uses a traffic simulation software called PTV Vissim to run traffic scenarios along Deerfoot Trail and through the city as part of his masters’ thesis on traffic engineering.

A masters student in transportation engineering at the University of Calgary thinks we could get traffic moving along Deerfoot Trail more quickly at peak hours if we’d just slow down a bit.

Karan Arora, working under supervisor Dr. Lina Kattan, is studying techniques to make transportation systems more reliable. Part of that work involves running simulations of traffic throughout the city under different scenarios.

“Many people think if the speed is more, the travel time would be less – but it’s actually opposite (at certain times),” said Arora. “There is the maximum capacity of the road.”

He said once any highway nears its capacity, as the Deerfoot often does at peak times, speed can cause an increase in congestion.

Arora’s solution – which is already being used in Germany and parts of the US – is variable speed limits. He said digital signs can be adjusted to the conditions of the road to keep things moving smoothly.

“Smooth traffic is very important,” he said, adding that by slowing things down from 100km/h to 80 or 90km/h, drivers could avoid the stop-and-go conditions that really make driving tedious.

In off-peak hours, he said 100 or 110 would be a perfectly acceptable speed limit.

Washington State already has variable speed limits on five corridors. Its Active Traffic and Demand Management system was launched in 2010 and cost $63 Million US according to the state’s website.

Although he has not crunched the numbers, Arora’s certain a variable speed system could get results for a fraction of the cost of adding more lanes to the highway to increase its capacity.

Any investment in such a system would likely fall to the province according to Coun. Shane Keating, chair of the city’s transportation and transit committee. He noted Deerfoot Trail falls under the province’s jurisdiction.

The other obvious question about adjusting speed limits is enforcement. Arora’s solution for this is simple. He said heavy enforcement with photo radar is what’s used in other jurisdictions that have tried this.

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