Responses to Centre Street Bridge Closure: Where the “Disappearing” Travelers Went

An ongoing topic of interest in urban transportation engineering is the impact of changes in road network capacity on the amount of vehicle travel in an urban area. In many cases, the debate focuses on potential increases in vehicle travel that occur with increases in road capacity—the phenomenon of “induced demand.” Some studies have also looked at the effects of reductions in roadway capacity and found that, in many of these cases, reductions in vehicle travel occur, generally confirming that a relationship exists between roadway capacity and vehicle travel. Additional information is provided on this subject in a North American context. The city of Calgary, in Alberta, Canada, is a major urban center with a population of over 850,000 and a downtown employment of over 100,000. Centre Street Bridge is a major road bridge across the Bow River that connects downtown Calgary to the residential area in the northern part of the city. The bridge carries over 34,000 vehicles per day, with heavy peak-period flows. In August 1999, the Centre Street Bridge was closed to car and truck traffic for 14 months for major repairs. A detailed study was undertaken of changes in traffic and in transit and pedestrian flows that took place in weekday travel patterns during the closure. This included both analysis of observed count data before and during the closure and an interview survey with over 1,300 car users of the Centre Street Bridge and the other bridges serving the north side of the downtown. The major findings of this study are summarized here. Particular emphasis is placed on explaining what happened to the vehicle trips that used the bridge before the closure.