Module 8 : Specialized Traffic Studies

Lecture 44 : Congestion Studies

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	Measurement of congestion Need and uses of congestion measurement Congestion has to be measured or quantified in order to suggest suitable counter measures and their evaluation. Congestion information can be used in a variety of policy, planning and operational situations. It may be used by public agencies in assessing facility or system adequacy, identifying problems, calibrating models, developing and assessing improvements, formulating programs policies and priorities. It may be used by private sector in making locational or investment decisions. It may be used by general public and media in assessing traveler's satisfaction. System performance measurement Performance measure of a congested roadway can be done using the following four components: Duration, Extent, Intensity, and Reliability. Duration Duration of congestion is the amount of time the congestion affects the travel system. The peak hour has now extended to peak period in many corridors. Measures that can quantify congestion include: Amount of time during the day that the travel rate indicates congested travel on a system element or entire system. Amount of time during the day that traffic density measurement techniques (detectors, aerial surveillance, etc.) indicate congested travel. Duration of congestion is the sum of length of each analysis sub period for which the demand exceeds capacity. This component measures the performance of a particular road in handling traffic efficiently i,e.,with the increase in the duration of congestion, poorer will be the performance of the transportation system. The maximum duration on any link indicates the amount of time before congestion is completely cleared from the corridor. Duration of congestion can be computed for a corridor using the following equation: For corridor analysis, $$H=N \times T$$ (1) where, $H$ is the duration of congestion (hours), $N$ is the number of analysis sub periods for which $v/c > 1$, and $T$ is the duration of analysis sub-period (hours). For area wide analysis, $$H_i=\frac{T\frac{v_i}{c_i}(1-r)}{1-r(\frac{v_i}{c_i})}$$ (2) where, $H_i$ is the duration of congestion for link $i$ (hours), $T$ is the duration of analysis period (hours), $r$ is the ratio of peak demand to peak demand rate, $v_i$ is the vehicle demand on link $i$ (veh/hr), and $c_i$ is the capacity of link $i$ (veh/hr).