Congestion Deficiencies

Background

Congestion limits the effectiveness of previous roadway investments, delaying travelers, increasing the risk of vehicular crashes, and degrading regional air quality. As vehicle volume on a corridor increase, the number of people passing through a corridor grows, until a point where the road becomes saturated and reaching its highest capacity.  Any additional vehicle volume decrease the person throughput of the roadway, referred to as the capacity cliff. 


Congestion deficiencies

Arterial Congestion
Arterial segments are considered congested if the average speed is less than or equal to 20 mph for any hour during AM peak (7-8 and 8-9 AM) and PM peak (4-5 and 5-6 PM) periods for any worst month.

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Planning Time Index

The planning time index represents how much total time a traveler should allow to ensure on-time arrival 95% of the time (Adequate 19 out of 20 Days).  The planning time index compares near-worst case travel time to a travel time in light or free-flow traffic. For example, a planning time index of 1.60 means that, for a 15-minute trip in light traffic, the total time that should be planned for the trip is 24 minutes (15 minutes x 1.60 = 24 minutes).

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Freeway Congestion

Freeway congestion compares travel speed in congested times to free flow travel speeds.  This measure is limited because it does not describe the reliability of the corridor, which is what travelers actually plan for when making travel decisions.  

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