Design Guide for Addressing Nonrecurrent Congestion (2014) / Chapter Skim
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3This chapter addresses the causes of nonrecurrent congestion, illustrates how nonrecurrent congestion is related to delay and reliability, and describes the costs associated with both delay and reliability. NONRECURRENT CONGESTION Traffic operational delay to motorists results from both recurrent and nonrecurrent congestion.
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4DESIGN GUIDE FOR ADDRESSING NONRECURRENT CONGESTION There are six main causes of nonrecurrent congestion: • Traffic incidents • Severe weather • Special events • Work zones • Demand fluctuations • Traffic control devices Each of these causes has specific characteristics that should be considered when attempting to quantify the nonrecurrent congestion they cause and the extent to which the design treatments presented in this guide may reduce it. Some of the important considerations associated with each of the six causes of nonrecurrent congestion are presented below.
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5DESIGN GUIDE FOR ADDRESSING NONRECURRENT CONGESTION surface before a storm to limit accumulation of snow and ice. Some design treatments increase the speed and efficiency of lane-clearing practices to get roadways operating at full capacity as soon as possible during and after a weather event.
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6DESIGN GUIDE FOR ADDRESSING NONRECURRENT CONGESTION incidents, special events, and weather more than they would have been before the presence of the work zone. Design treatments aimed at reducing the impact of work zones typically accomplish one of three things: • Minimize the capacity lost due to the work zone.
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7DESIGN GUIDE FOR ADDRESSING NONRECURRENT CONGESTION TRAVEL TIME RELIABILITY The more often nonrecurrent congestion occurs, the less reliable the roadway is, and the more often drivers find that the time they have allocated for their trip is incorrect. For roadways that experience frequent nonrecurrent congestion, drivers often have to allocate more time to their trip than is normally required to ensure that they arrive at their destinations on time most of the time.
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8DESIGN GUIDE FOR ADDRESSING NONRECURRENT CONGESTION intuitive understanding of how events cause unexpected delay. As a result, they will pad their budgeted travel time to account for the possibility of unexpected delay so that they will arrive at their destinations on time (even if this means arriv ing early on some days)
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From page 11... ...
9DESIGN GUIDE FOR ADDRESSING NONRECURRENT CONGESTION practices may affect the frequency of use and effectiveness of the treatment. As an example, crash investigation sites are affected in both ways.
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