Abstract:
Urban traffic is growing from day to day following a high demand along the roads. This traffic
growth contributes a bottleneck at bridge approaches with constricted widths. In Jimma town,
vehicles passing the town are increasing, and causing traffic congestion along the highway,
particularly where the bridges are located. Effects of constricted width pavement at Bridge
Approach on traffic flow caused a dilemma to the town administration regarding which
appropriate measures to implement. This study focused on five bridges along the main
thoroughfare in the town. These five bridges observed with narrowed or constricted width
approaches relative to the width of approach roads. Collecting observed traffic survey was
conducted for continuous 12hrper day using both tally and video recording. A stratified
sampling technique was used to determine the minimum number of end-users or respondents to
answer the structured questionnaire survey. The respondents like a pedestrian, driver, traffic
police, engineers, and others were taken part. Regression analysis was used to correlate the
dependent variable with an independent one. AutoCAD, PTV Vissim, SPSS, and R-codes
software were used for data analysis and interpretation. As per the study, traffic flow
characteristics like travel speed, traffic density, and traffic flow were identified per bridge
location from both primary and secondary data sources. Traffic composition of different
motorized and the non-motorized vehicle was also observed along a bottleneck structure.
Vehicles like animal carts, bicycles, motorcycles, small cars, medium cars, and large cars were
observed along with a bottleneck structure. Traffic crashes like rear-end, head-on, sideswiping,
and others were observed all over the bridges. "Best fit model "was also formulated to predict
the effect of constricted width Pavement Bridge Approach on current and future traffic flow.
Possible remedial actions like widening bridge width, smoothening sudden constriction,
constructing cost efficient pedestrian walkway and installing traffic guide warning sign was
suggested to reduce negative effect of constricted width Pavement Bridge Approach on traffic
flow. From the result, it was observed that constricted width Pavement Bridge Approach
profoundly affect traffic characteristic and travel safety of end-users. In the future, traffic flow
along this structure would be a danger. Possible remedial action like a widening bridge shall be
taken to smooth traffic flow
