Road safety auditing approach in assessing safety hazards of a selected highway section of Bangladesh

Abstract

The main objective of this research was to assess potential safety hazards of Dhaka-Mawa Highway using road safety auditing approach and to recommend possible options for remedial treatment. At first existing “Guidelines for Road Safety Audit, 2005” of Roads and Highways Department (RHD), Bangladesh is reviewed and guidelines of developed countries are analyzed to find out deficiencies of RHD guidelines. Checklists provided with RHD guidelines are also analyzed and design standards and guidelines of other countries are studied to develop a more detailed and complete checklists. Then using the modified checklists, road safety auditing was conducted for Dhaka-Mawa highway. Accident data was collected to supplement audit findings. Attempts were made to assess the safety hazard scenario and to suggest likely remedial measures in view of the construction of proposed Padma Bridge, rapid urbanization and implementation of 4-laning project. In order to achieve the objectives of the research work, various guidelines on road safety audit, design standards, as built drawings, proposed road alignment plan and related publications were consulted. A total of 13 field visits were made to observe possible hazards through conducting highway geometric study, site specific speed studies, vehicular and pedestrian counts etc. Local traffic conditions were critically observed during the whole study. Besides, a total of 11 visits were made to collect accident data from 5 police stations. Review of ‘existing RHD guidelines on road safety’ identified the necessity of incorporating few important aspects in the manual. Noteworthy aspects are: composition and qualification of audit team, roles and responsibilities of various parties, steps of audit process, quality assurance procedure, legal issues and areas of concern, costs and benefits of audit, monitoring and evaluation (M&E) procedure, explanation of audit stages etc. Considering the local road traffic peculiarities and basing on road safety guidelines of experienced countries, the study identified some relevant issues for inclusion in the audit checklists. Striking issues are: scope of the highway, accessibility, night inspection, hazardous locations, side roads, speed-breakers, road user behavior, enforcement, trauma management, non-standard vehicles etc. Following the checklists developed in this research work, potential safety hazards along the highway were systematically identified. Presence of 11 highway-adjacent educational institutions, 14 filling stations and 15 sites of past crashes shows the high intensity of hazard exist along the highway. Field measurement revealed inadequate Stopping Sight Distance (SSD) and Passing Sight Distance (PSD) at three curves (available sight distances at curves prior to Shologhar, Chonbari Junction and Srinagar Ferryghat are 394 ft, 291 ft and 289 ft respectively against required SSD i.e. 461.53 ft and required PSD i.e. 1657.02 ft). Measurement taken at curves discloses that curve widening is not considered for 12 sharp curves of the corridor. Particularly data analysis for curve prior to Srinagar Ferry Ghat shows that 1.5 feet and 2 feet curve widening is required for design speed of 60 kmph and 80 kmph respectively. Vehicular flow data, pedestrian intensity count as well as associated site specific safety hazards revealed the necessity of overpasses at five locations. As a whole, this corridor is assessed as hazardous mainly due to: wide range of 85th percentile speed (57 to 62 kmph) , heterogeneous vehicle composition (nonstandard motorized vehicle comprises 58% and 30.92% of vehicle composition observed at two places) causing speed differential of 15 kmph and modal speeds between 44 to 46 kmph, significant variance of speed between locations and also within the same type of vehicles (average speed of bus, truck, small standard motorized vehicles and non-standard vehicles was found to vary between 49-57 kmph, 35-51 kmph, 59-66 kmph and 28-46 kmph respectively), observance of motorized vehicles’ speed between 16 kmph to 23 kmph due to various hazards at bazaar/built-up area/bus-stands etc. In addition, along 31 km route length, change of alignment at every 1.68 km length due to presence of 19 curves, high (15 to 25 feet) and steep embankments having non-traversable batter slopes (1:2), presence of one hazardous location per 1.82 km length of the highway, existence of bottlenecks i.e. narrow bridges at each 1.72 km length , existence of one untreated junction per 1.29 km length of the highway, installation of 0.94 non-standard risky speed reducing devices per kilometer of the highway etc. have increased the level of roadway hazards significantly. Moreover, field observation reveals that along this corridor drivers of heavy vehicles particularly of buses (which is 36.08% of total traffic), are always in fierce competition and also have the tendency of making risky overtaking maneuver which is often induced by presence of slow moving vehicles resulting unsafe and hazardous traffic operating condition. To supplement safety audit findings accident data of 9 years was collected. Accident statistics shows predominance of pedestrian related accidents (38.30%) followed by head-on collision accidents (13.36%), rear end collision accidents (7.13%), loss of control accidents (10.02%) and other types of accidents out of total 449 reported accidents. Analysis also shows that there exist 25 hazardous locations where a total of 301 accidents had occurred (i.e. 67% of total accidents). Bus is found to be the most dominating vehicle involved in 53.45% (240 numbers) of total reported accidents and 58.72% (101 numbers) of pedestrian related accidents. According to user groups, pedestrians are observed to be the victims of accidents (172 accidents or 38.30%) followed by passengers of various vehicles (153 accidents or 34.07%). Various contributory factors to accidents are identified during road safety auditing. It is anticipated that proposed construction of Padma Bridge and 4-laning project is likely to aggravate already deteriorated safety situation substantially due to increased AADT which is forecasted to be 9317 in 2014 and 17185 in 2020 and also due to rapid change of land use pattern along the corridor. Consequential major impacts on road safety are likely to be due to increase of side road connections, high level of conflict among various types of vehicles particularly through and local traffic, increased number of hazardous locations, increased roadside non-motor activities, untreated divider opening etc. Basing on audit findings, short/mid/long term and low/high cost remedial measures were suggested in details in the audit report. Noteworthy remedial measures are: provision of service roads for non-standard motorized vehicles and non-motorized vehicles, construction of vertical bypasses (approximately of total 4 km length) and conversion of cross-junctions to staggered T Junctions at identified hazardous locations, straightening/realignment of the highway at 12 sharp curves, provisioning of W-beam type safety barriers at embankment having steep batter slopes , treatment of 24 non-engineered junctions , construction of pedestrian overpasses at 5 locations, introduction of company-based organized bus service, establishment of segment-specific speed limits etc. In addition to the recommendations made in the audit report, the study also proposed few suggestions to mitigate probable safety hazards to be aroused due to proposed Padma Bridge, 4- laning project and expected rapid urbanization. Worth mentioning suggestions are: strict access control to national highway, development of highway-adjacent land use policy, building up of local road network, upgrading three at-grade junctions (Hasnabad BRTA T Junction, Kodomtoli Tjunction and Mawa Roundabout) by constructing grade separated interchange facility etc. In regards to 4-laning project, the study suggested treated opening instead of normal opening without provision of turning refuge and New Jersey type barrier instead of low height divider. Particularly in case of 4-laning project, it is recommended that instead of providing 4 lanes for all users, central two lanes should be allocated for through traffic and other two lanes should be developed as service roads to accommodate local traffics. The study ended with few topics for future studies.