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Investigation of Solutions to Recurring Congestion on Freeways
Mazzenga, Nicholas J.
Michael J. Demetsky
Year: 2009
VTRC No.: 09-R10
Abstract: Persistent daily congestion, which has been increasing in recent years, is commonly experienced for several hours or more during the morning and evening on Virginia's urban freeways. Many of these roadways are at or near capacity, which causes severe delays and backups. One solution to reducing recurring congestion is to add capacity by building more lanes; however, this is usually the last resort as it is an expensive and time-consuming approach. Another strategy proposed to combat recurring congestion is to manage the current freeways so that they operate more efficiently. Reducing congestion through better managed freeways has numerous documented benefits, including reducing travel times, smoothing the traffic flow, increasing average fuel economy, shortening the rush hour period and reducing vehicle queuing. The highway operational strategies implemented to reduce recurring congestion have shown promising results abroad where there is an extensive use of active traffic management systems. To prove the effectiveness of a better managed freeway in mitigating recurring congestion, this study tested the effectiveness of an active traffic management system on a simulated model of I-66 and I-95 in Northern Virginia. Hard shoulders, variable speed limits, and ramp metering are several active traffic management systems simulated in this study. The simulation model was based on the geometric characteristics, ramp volumes, vehicle flows, and speeds of actual recorded conditions. Compared with the simulated control conditions, the results of the study indicated improvements in average fuel economy, travel delay, delay of the onset of congestion, and reduction of queues. The two active traffic management systems, i.e., variable speed limits and hard shoulders, showed the highest potential for reducing recurring congestion and should be considered as potential countermeasures in congested corridors. Although the capital costs of implementing these strategies would be high, the return on investment in the first year of operations is estimated at $500,000, with the potential to grow to as much as $8 million annually in subsequent years.