Canadian Consulting Engineer
Roundabout at BOUT-DE-L’ILEEngineering
Modern roundabouts remain relatively rare in Canada. At the time the "Carrefour giratoire du Bout-de- l'Ile" was constructed on the eastern tip of the Island of Montreal, Quebec had only 10 roundabout...
Modern roundabouts remain relatively rare in Canada. At the time the “Carrefour giratoire du Bout-de- l’Ile” was constructed on the eastern tip of the Island of Montreal, Quebec had only 10 roundabouts, most of them small and with little traffic. This roundabout is designed to carry 30,000 vehicles a day and is located at a key traffic gateway.
While they may look similar to the ancient traffic circles of the 1950s, roundabouts operate quite differently. Traffic circles often included traffic lights in order to control the various movements, whereas with roundabouts, vehicles entering the circulatory roadway must yield to those already in it, eliminating unnecessary stopping and making it a safer and more efficient option.
Designed by Sguin ingnierie as the prime consultant, the Bout-de-l’Ile roundabout is located at the intersection of Sherbrooke and Notre Dame Streets, two major Montreal arteries, near where they merge onto Le Gardeur Bridge. The Gardeur is one of only two bridges linking this area of Montreal Island to the northern shore of the St. Lawrence River, the other being Charles De Gaulle bridge. The roundabout therefore sits at the starting point of the road network onto Montreal Island and downtown. To the north is the bridge and Highway 138, which extends all the way along the north shore of the St. Lawrence to Trois-Rivires and Quebec City.
The idea of a roundabout leading to this important bridge crossing was first viewed with concern due to the negative opinion that many people had of traffic circles. However the idea gained acceptance and won the support of city of Montreal authorities, who resolved to make the roundabout a model for this type of highway construction.
Three branch circle
In order to process the heavy traffic, the roundabout was designed in the form of a three-branch circle flanked by two bypass lanes. The combination of roundabout and bypass lanes is a creative configuration that ensures high traffic capacity while substantially reducing the average vehicle speed, which has dropped from 70 km/h to 35 km/h.
The bypass lanes, one from Le Gardeur Bridge toward Sherbrooke Street and the other from Notre-Dame Street toward Le Gardeur Bridge, help to prevent the roundabout from blocking traffic in the morning and evening rush hours. The presence of two lanes in the circulatory roadway also allows for ample traffic flow and provides sufficient width for large semi-trailers. In addition, a mountable apron, or curb, at the centre of the roundabout allows for the passage of oversized trucks that require greater width than the two available lanes.
Pedestrian sidewalks and crossings were incorporated into the design. The sidewalks follow the shape of the roundabout, with pedestrian crossings at the entry and exit lanes. Pedestrians can cross in several stages over narrow lanes, thanks to the refuge provided by the splitter islands at the centre of each branch.
The roundabout’s geometry and design allow large surface areas to be reserved for landscaping. While the total paved surface of a roundabout is about equal to that of an ordinary intersection, the roundabout design allows for more space between lanes, thus breaking down the mass of pavement.
The landscape design was influenced by the historic and heritage character of the area, and incorporates the same kinds of plants that grew when the lands were a seigneurial domain.
Innovations in lighting and signage include the use of special street lamps at pedestrian crossings. LED chevrons, whose intensity can be adjusted to different ambient levels, are placed on the centre island. There are also remotely controlled safety cameras, accessible via a dedicated web site, to allow operators to monitor traffic in real time.
The final cost for the project was $10 million, including demolition of the old elevated interchange it replaced. The project was completed on schedule between July 2005 and July 2006.
The project won a 2007 award from the Association of Consulting Engineers of Quebec (AICQ).
Client: City of Montreal
Prime consultant: Seguin ingnierie (Yvan Cot, ing., ric Fortier, ing, Stephan Kellner, ing., Peter Soland)