Alan T Brownlee

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.

Incremental Modeling Developments in Sacramento, California: Toward Advanced Integrated Land Use-Transport Model

The regional transportation planning agency in Sacramento, California, is taking a three-pronged approach to updating its land use-transportation forecasting models: developing a long-term model design, improving existing models toward that design, and collecting data that can be used to support the existing models while the new design is being developed. The advanced integrated model design contains a tour-based travel model involving microsimulation of individual tours of synthetic households, a microsimulation-based land development model, and a spatial input-output model of the regional economy. The existing models consist of a land use model based on the MEPLAN model, a traditional four-step model of transportation demand improved with the addition of an automobile ownership submodel and joint consideration of mode and destination for work trips, and an interactive neighborhood-level parcel allocation system. The process described is one of improvement of current models and of moving toward a new model design while the agency faces ongoing modeling needs and uncertain budgets.

Unifying Long- and Short-Distance Personal Travel in a Statewide Planning Model

A disaggregate behavioral tour-based microsimulation model was developed to forecast intrastate long-distance personal travel on a typical weekday as part of an overall statewide travel model system for all residents of California. A novel approach to what is traditionally described as travel generation was developed as a series of choice models focusing on consistency and integration with other components of the model system. Key features include the explicit integration of this long-distance personal travel model with the complementary short-distance personal travel model, the specification of a travel party size model for long-distance travel based on household size, and the development of models to represent characteristics of the long-distance travel tour, including duration of tour (number of nights), travel day status for a typical weekday, and time of travel within the weekday. The explicit trade-off between long- and short-distance travel produces appropriate sensitivities and reproduces the real-world phenomenon of rural travelers producing more long-distance travel. Subsequent models not described in detail in this paper take advantage of this information; in particular, party size has a significant effect on mode choice. The model system is operational and has been calibrated and validated.