22. Evaluation of Effects of Carriageway Obstructions on Heterogeneous Traffic
Date of Start

August 2005
Indian Institute of Technology Madras (R, C)


Scope and Objectives

The scope of this study covers only fixed obstructions on the carriageway edges, in mid-block sections of selected four-lane divided roads in Chennai city. Three mid-block sections, with obstructions on their carriageways were studied. The study covered only the effect of single obstruction on the traffic, obstructions in series have not been dealt with. This study deals with finding the effect of the obstructions, which are present on the carriageway, on traffic in terms of capacity reductions, speed reductions and variations in headways. Thus, variations in capacity, mean speeds, speeds of vehicles of different classes of vehicles, headways are determined due to the obstruction present on the edge of the carriageway.

• To identify the types and nature of obstructions present on the carriageway edges, considering Chennai as a case study.

• To study the speed and flow variations due to the obstructions on the carriageway edges.

• To study the speed variations in the traffic stream between different categories of vehicles.

• To study the effect of these obstructions on longitudinal gaps (i.e., headways) between the vehicles.

• To draw conclusions on the adverse influence of these obstructions on traffic flow.

Data Collection
• Reconnaissance survey
• Identification and selection of study sites
• Traffic data collection through videography
• Measurement of geometric features of the study locations

Data Analysis
• Volume count - 5 minutes intervals
• Mean traffic speeds for each interval using IrfanView
• Speeds of different classes of vehicles for the same interval
• Finding differences in speeds
• Average headways for each 5-minute interval using IrfanView
Findings and Conclusions
• Due to the obstruction present on the edges of the carriageway, there is a reduction in flow capacity of the road.

• The capacity reduction depends on the distance of the obstructions from the edges of the carriageways. As the distance from the edge increases, more is the impact of obstruction on the capacity reduction. In this study it ranged from 2.4 – 5.4 % in the case of four-lane divided roads when the distance of the obstructions was between 0.5 and 1.2 m.

• The reduction in the mean speed is in the range 10 – 13 % and is also dependent on the distance of obstructions from the edge of the carriageway.

• The reduction in speeds of two wheelers is insignificant, which is believed to be due to acceleration –deceleration characteristics, sleekness of the two wheelers and most importantly driver behavior of two wheeler drivers.