Effect pedestrian underpasses on traffic flow characteristic in metropolitan Dhaka

Abstract

The aim of this study was to investigate the effectiveness of pedestrian underpasses in Metropolitan Dhaka. The locations of the underpasses studied were at Karwan Bazar and at Gulistan Square. In order to determine the performance of these underpasses data were collected both 'before' and 'after' their construction. Manual as well as video recording methods of data collection was applied in this research study. Data has been analyzed both qualitatively and quantitatively by observing data critically and applying standard statistical method. For quantifYing the effectiveness of underpasses - classified vehicular flow, travel time, speed and pedestrian flow, crossing time, speed as well as vehicularpedestrian conflicts were selected as the measure of effectiveness (MOE). From observational studies it has been seen that in general, expectedly pedestrians do not voluntarily use grade-separated facilities unless they are forced to do so either by median barrier or temporary barrier created by bumper-to-bumper jam condition. Moreover, relatively pedestrians compliance of using footbridges is very poor especially where these facilities are constructed very near to the junction. It is mainly because of the fact that in the junction no restriction measure like median barrier can be installed and periodic gaps are automatically created by signal or forcefully by traffic police. Findings of Karwan Bazar Underpass The 'before and after' statistical analysis of data has shown that the underpass at Karwan Bazar site has improved all the measure of effectiveness (MOE) significantly. The overall vehicular flow improvement in morning hour was 20% & 7.9% and in afternoon hour it was II % and 6.6% for South to North and North to South directions of traffic flow respectively. Relatively, flow improvement is found higher in the morning shift. On average travel time for different types of vehicle increased by 18% to 40% in S-N direction and 10% to 34% in N-S direction of travel. Similarly speeds of each category of vehicle have increased significantly ranging 8-22 kmph (22-64%) and 3-13 kmph (11- 52%) in S-N and N-S directions respectively. Overall, construction of underpass at this site has improved the travel time and speed of traffic stream in both directions by 26-30% and 34-44% respectively. Corresponding average delay savmgs were also very significant. The amount ranges 8-31 sec in S-N direction and 6-25 sec in N-S direction while traveling 440m and 480m segments of road in respective direction. The dispersion parameter or standard deviation (Sd) of travel time data has shown that due to construction of underpass, in the study-segment of the road, journey become very smooth and comfortable. Statistical analysis results have shown that the pedestrian flow has increased significantly in both shifts. In the morning shift pedestrian flow value has increased by 36.5% and 45.4% in afternoon shift. This extra flow can be attributed to 'attracted flow' to the new improved facility. The vehicular-pedestrians conflicts study has shown that before underpass construction, during the study period about 75% pedestrians had to face risky crossing interrns of accepting very small gaps and crossing quickly or creating gaps forcefully in the speedy traffic stream. It has also found that most of the pedestrians find it difficult to cross the road individually. The proportion of group crossing has been found to be 85%. Moreover, it has revealed that due to hostile attitude of motorists about 30% pedestrians had to take multiple attempts to negotiate with the drivers and to complete the crossmg maneuver. From the 'before-after' analysis it is found that pedestrian travel time has increased by 11.1% (7 sec) as compared to at-grade crossing. Before underpass construction, average crossing speed of individual pedestrian was 1.05 m/s in the morning and 0.92 m/s in the afternoon hour. In case of pedestrian group-crossing, average crossing speed was found much lower (0.6m/s) than that of average individual crossing speed (1.0 m/s). Findings of Gulistan Square Underpass It is observed that at this site most of the pedestrians avoid the underpass due to slow speed of traffic stream as well as lack of restrictive measures. As such the underpass construction at this site has failed to improve both traffic operation as well as pedestrian safety significantly. Guidelines for Planning of Grade-separated Facilities Based on the findings of this study, understanding of the factors contributing to the effectiveness of the underpasses which may lead to better design of these facilities in the future are listed as follows: Grade-separated facilities should not be constructed: o Without restrictive measures viz. continuous median barrier or footpath railing o Near the junction especially where there is signalized or police controlled zebra crossmg o At narrow roadway o Where parking problems exits o If traffic stream comprises non-motorized vehicles For planning of grade-separated facility, in general preference should be given as follows: o In selecting facility-type: Footbridge over underpass o In selecting bridge-type: Steel-footbridge over R.C.C-footbridge o In selecting access-type: Ramp over stair o In selecting location: Mid-block position over 'at or near' junction o In selecting median barrier: Modified New Jersey (see Figure 5.1) over typical railing barrier