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Evaluation of Urban Freight Deliveries using Microsimulation and Surrogate Safety Measures
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    Freight deliveries on signalized urban streets are known to cause lane blockages during deliveries. When delivery vehicles block lanes of traffic near signalized intersections, the capacity of the intersection is affected. Current practice is for traffic signals to be timed assuming that each approach can serve vehicles at the unobstructed saturation flow. There are three goals of this research: 1) to develop models to quantify the capacity and delay effects of a lane-blocking freight delivery on a signalized urban street, 2) to develop a model for adapting the traffic signal timing in real time for signal cycles during which a delivery blocks a link upstream of the intersection, and 3) to quantify the safety impacts of freight deliveries. The results of the queueing model show that accounting for the dynamics of queuing provides closed-form analytical formulas for delay and capacity that can account for varying locations of deliveries and different impacts on different lane groups. The signal control algorithm requires real-time information about the location of the double-parked delivery vehicle, which is assumed to be available from connected vehicle data from urban freight vehicles or from another detection system. The results show that for low levels of traffic demand, the signal control method reduces intersection delay compared to a signal that is timed for unblocked traffic. The algorithm also keeps the intersection approach undersaturated for higher levels of demand, which is important because deliveries can last for many signal cycles. For the safety analysis, the number of conflicts follows a similar pattern as delay with a decrease in number as freight stops move away from the intersection. The crash severity does not appear to change significantly. This study suggests that any measures that can be taken to encourage delivery stops to be made near the middle of the block would be effective for improving traffic flow and safety. Managing freight deliveries in this way is likely to be more feasible than attempting to ban double parking altogether.
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