Thursday, November 17, 2011

Traffic Accidents and Optimum Congestion Charges

Traffic Congestion and Accidents(26 page pdf, Andrea Schrage, University of Regensburg Working Papers in Business, Economics and Management Information Systems, Nov.9, 2006)

Congestion Pricing Equilibrium
The report reviewed today looks at the calculation of optimum congestion charging with the cost of accidents included in that calculation. To do that the author considered the timing of the accident (earlier or later during the daily rush hour) and how an accident could be factored into the modelling needed to estimate an optimum pricing.

Key Quotes:

“Congestion arises from high levels of travel demand or demand that is strongly concentrated during short peak periods, the latter resulting in pronounced rush hours

“By temporarily reducing the amount of road space effectively available, accidents can be triggers of traffic congestion suffered by any given amount of subsequent traffic …some 25-30% of delays are estimated to be the consequence of traffic accidents

“An accident typically blocks one road lane for 45-90 minutes, causing time losses of 1200- 5000 vehicle-hours. Price this delay at the average value of travel time, say e15 per vehicle-hour, to calculate the congestion costs of an accident.. external costs of accident-induced congestion amount to e0.005- 0.023 per vehicle kilometer “

“If no toll is charged, traffic flow will constantly adjust such as to equalize the expected private cost of driving at different times, including the expected travel delays from possible accidents, but ignoring externalities”

“the optimal static marginal cost of congestion tends to be lower early during the rush hour than at later times. This is because a higher traffic flow causes not only congestion at the time of usage but also higher expected congestion later on”

“it is important to distinguish between congestion as a pure traffic flow problem and additional congestion that results from traffic accidents.. an efficient road toll also charges the additional congestion costs caused by an accident to the drivers responsible for that accident (or rather the expected value of that cost to every driver)”
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