Modeling Highway Congestion Index for a Developing Country: The Iran Experience

This paper describes an attempt to develop congestion indices for a developing country with
a limited sampling. Speed and
ow rate information was collected from urban highway trac

ow videotaping in Iran. Video display provided information for trac modeling when, similar to
most of the developing nations, Iran does not have locally developed highway capacity manuals.
Processing of the extracted data and trac modeling provided free and capacity
ow information
for the selected freeway and principal arterial sections for the capital city of Tehran. The
congestion indices were associated, in simple and logical models, with ve trac descriptive
variables of travel speed, travel rate, delay rate, travel rate ratio and delay ratio, respectively.
To calibrate the congestion index models, specic congestion levels were assessed by the index
values under free and capacity
ow conditions. The functional forms used in congestion index
modeling were derived from the congestion rate of change, simple, reasonable and relevant
assumptions. For comparison, index models, based on the US Highway Capacity Manual, HCM,
speed and
ow rate information, were also developed. The developed indices were suggested
as feasible and included quick response measures for congestion monitoring and control when
trac management resources are often limited and scarce. Based on the preferences of a group
of transportation professionals and university students, the relative importance of each of the
individual indices, as average weighting value, was identied. Using the average weighting values,
an overall congestion index was also developed. The overall congestion index was suggested as
a complimentary or alternative measure for congestion intensity assessment and evaluation. The
study ndings were based on a rather limited database and were location specic; nevertheless,
for quick response congestion index development, the applied methodology could be used by any
developing country. The suggested indices have potential in trac management and congestion
mitigation.