How lower speed limits on Deerfoot Trail traffic could actually speed up your commute

Deerfoot Trail to close some lanes overnight on Tuesday, Wednesday

Slowing traffic down on Deerfoot Trail during rush hour could actually speed it up, says a University of Calgary grad student studying transportation engineering.

Karan Arora spoke to the Calgary Eyeopener Tuesday about the benefits of variable speed limits.

Using digital signs to change the speed limit  — based on road, traffic and weather conditions  — is a system already in place on roads in Germany and Washington State, Arora said.

By having motorists travel at a slower but more consistent speed, stop and go traffic is reduced and the overall speed improves for everyone.  

"The main objective is to have increased flow and reduced travel time," said Arora, who has been using different models to study the impact of such speed limits on roads in Calgary.

Lower speed limit during rush hour

Arora said traffic exists in two states: it's either congested or not congested.

"The congested state is very sensitive and any small disturbance within the flow, for example a sudden change in lane by a particular vehicle, can trigger stop and go conditions," he said.

Slowing down the speed of motorists on Deerfoot Trail when traffic is heavy could prevent such congestion, Arora said.

"During rush hour the speed would be less than 100 km/h and during off peak hours it will again be reached to its maximum value," he said.

"And even if during off-peak hours [there are] any accidents, the variable speed limit will again come into effect and make sure traffic will be smooth."  

Calgary's oldest and busiest freeway 

Arora said introducing variable speed limit signs would cost just a fraction of the price of adding more lanes to Deerfoot Trail to address congestion.  

Variable speed limits are just one idea being studied at the Schulich School of Engineering to improve traffic conditions, Arora said. 

The City of Calgary and Alberta Transportation are currently working together to study Deerfoot Trail, Calgary's oldest freeway and the busiest in Alberta.

Recommendations on short-term improvements for safety and mobility are expected to be shared in early 2017, according to the city's website, with long-term recommendations available by the end of 2018.

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With files from the Calgary Eyeopener