Expressway Single-Lane Work Zone Capacities with Commercial Vehicle Impacts

Like other government transportation agencies, the Ontario Ministry of Transportation performs regular maintenance and reconstruction of freeways across the province. If lane closures are required for this maintenance, they have to occur during a window of time in which travel demand is below the capacity of the remaining open lanes. To date, the estimates of capacity for single-lane work zones have been based on relatively simplistic planning assumptions. The impact of heavy vehicles has not generally been considered and it has been observed that overnight construction windows defined on the basis of these assumptions are often subject to significant queuing and delays. In an attempt to understand work zone capacity, data was collected at seven work zones in the Greater Toronto Area during the fall of 2008. Analysis of this data indicated a wide and unexplained variation in the capacities achieved at the surveyed locations. It was hypothesized that the orderliness of the merging behaviour may be an important factor in the explanation of this variation, particularly the distance upstream from the lane drop location at which the vehicles in the dropping lane merge into the through lane. Using micro-simulation, the effects of different merging processes were evaluated and simulation outputs corresponding to the observed data were achieved. It was observed that there are two operational regimes, one with higher throughputs corresponding to early merging and relatively smooth operation in the remaining open lane. The second, with lower throughputs, involved late merging and interrupted flow in the open lane. These results are preliminary and would benefit from additional data collection and analysis oriented to the evaluation of this particular phenomenon.