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MAG Non-Recurring Congestion Study


JULY 2017
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The goal of this study was to determine the impact of Non-Recurring Congestion (NRC) on freeway and arterial traffic operations, and to identify suitable countermeasures for each road environment.

This study had two key objectives:

  1. Gain a better understanding of the role played by various random incidents related to traffic, weather, and special events that result in non-recurring traffic congestion on the freeway system and on the arterial system in the region.
  2. Identify effective countermeasures, best practices and recommend a plan to test them in the Phoenix metropolitan region.  These countermeasures should help regain some of the lost road capacity due to NRC, thus reducing the need for adding new road capacity.

Non-Recurring Congestion on both freeway and arterial systems have been identified, in general, as the unexpected traffic delays caused primarily by crashes and incidents, vehicle breakdowns, road construction activities, special events, extreme weather events etc.  In addition, NRC is also caused by rubbernecking motorists, police investigations at crash sites, in some instances by improper usage of Dynamic Message Signs that display long complex messages.  A number of existing programs in the Phoenix metropolitan region support traffic management functions that aim to mitigate the overall impact of NRC on traffic operations.  The ALERT emergency response team of Arizona DOT, responds to major crashes or hazardous material spills on the freeway system.  The Freeway Service Patrol, funded by MAG and operated by the Department of Public Safety, provides emergency roadside assistance to well over 10,000 motorists stranded on the regional freeway system each year.  The REACT traffic incident management team of Maricopa County, responds to incidents on the arterial street system within all unincorporated areas of the County, and within a few local communities in the west valley.

Nationally, it has been estimated that nearly 60 percent of all urban traffic congestion could be attributed to NRC.  However, until this study the NRC phenomenon had not been examined in detail in large metropolitan regions with well developed arterial street systems to clearly identify the true magnitude of its impact on freeways and on arterials. Oversight for this study was provided by a Study Advisory Group (SAG) which  consisted mainly of members of the MAG Intelligent Transportation Systems Committee.

The study carried out the  following tasks.

Task 1:

Literature Review of NRC, Potential Countermeasures

Task 2:

Develop a Methodology for Quantifying NRC and a Data Collection Plan

Task 3:

Data Collection, Analysis and Estimation of the Impact of NRC on Freeway and Arterial Systems, Transit and Freight

Task 4:

Identify Countermeasures & Required Resources

Task 5:

Develop an Implementation Plan

Task 6:

Develop the Framework for a Pilot Project

Task 7:

Final Report and Executive Summary

STUDY COST :  $ 298,954  
STUDY DURATION:  February 2010 – October 2011
STUDY TEAM :  A consultant team led by Lee Engineering LLC  performed this study.  The Texas Transportation Institute  also provided services as a subcontractor.

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