Easing Traffic Flow

February 2012

What happens when a municipality tries to deal with traffic flow by changing stoplight patterns or implementing one-way streets and bike lanes? Montreal’s Plateau Mont-Royal borough recently turned to McGill Professor Marianne Hatzopoulou to assess whether changes it had made were having the right impact on traffic flow and exhaust emissions.

Hatzopoulou and her team digitized the borough’s entire road network, including its bike lanes, topography and traffic lights.

“Students then went into the streets to collect data on stoplight timing and traffic flow. We simulated every car as it stops at intersections, accelerates, and so forth,” she says.

Besides studying the impact of the borough’s interventions in the direct vicinity, the team also modeled what effects the changes might have on other districts to determine if changes in the Plateau were simply shifting traffic congestion to other areas. “This was innovative,” Professor Hatzopoulou says, “because most researchers doing traffic simulations don’t look at regional effects.”

Innovative approach

Using commercially available Vissim software, the model provides a second-by-second profile of each vehicle as it accelerates and decelerates. Hatzopoulou also linked the data to a traffic emissions microsimulator, providing important information about how emissions were altered by shifts in traffic.

Fewer cars don’t necessarily reduce emissions, she points out. “Sometimes you have more emissions with fewer cars moving slowly and stopping than with more cars moving fluidly.”

Professor Hatzopoulou’s model can be adapted for traffic planning anywhere and as a result she has been approached by several municipalities and the Province of Quebec’s Ministry of Transport to help them address issues related to traffic and air quality.

Professor Hatzopoulou’s studies mesh with other traffic research in the Faculty of Engineering, notably that of Civil Engineering colleagues Luis Miranda-Moreno  and Naveen Eluru in the Interdisciplinary Research Group on Mobility, Environment, and Safety, and Urban Planning Professor Ahmed El-Geneidy and his Transportation Research at McGill (TRAM) group.

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