What effect does work activity have on traffic conditions in a work zone? This question has still not been answered satisfactorily in practice. Without knowing the true effect a work activity has on traffic, practitioners are forced to make assumptions while scheduling work. This report attempts to answer this question by studying the traffic flow characteristics for various work activities, i.e., traffic speed versus flow curves, capacity reduction factors, and free-flow speed reduction factors.
The importance of the speed-flow curves and reduction factors for work zone planning is also stressed in the latest edition of the Highway Capacity Manual (HCM). The HCM recommends capacity and speed reduction factors for work zones yet does not include specific guidance for including the impact of work activities.
Three traffic stream models, Gipps, Newell-Franklin, and Van Aerde, were calibrated using field data from St. Louis, Missouri.
The Van Aerde model offered the best fit with the field data compared to the other two models. Using the Van Aerde model-generated speed-flow curves, it was found that the capacity for bridge-related activities varied from 1,416 vehicles per hour per lane (vphpl) to 1,656 vphpl and for pavement-related activities from 1,120 vphpl to 1,728 vphpl.
The capacity reduction factor for different work activities was found to be in the range of 0.68 to 0.95, while the free-flow speed reduction factor was found to be in the range of 0.78 to 1.0. The methodology proposed in this report allows the incorporation of work activity effects into traffic impact assessment tools and results in quantitative guidance for work zone planning and design.