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Assessment of driver vision functions in relation to their crash involvement in India Ashish Verma 1,5, *, Neelima Chakrabarty 2, S. Velmurugan 2, B. Prithvi Bhat 3, H. D. Dinesh Kumar 1 and B. Nishanthi
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Assessment of driver vision functions in relation to their crash involvement in India Ashish Verma 1,5, *, Neelima Chakrabarty 2, S. Velmurugan 2, B. Prithvi Bhat 3, H. D. Dinesh Kumar 1 and B. Nishanthi 4 1 Department of Civil Engineering and 5 Centre for Infrastructure, Sustainable Transportation and Urban Planning, Indian Institute of Science, Bengaluru , India 2 Traffic Engineering and Safety Division, Central Road Research Institute, Mathura Road, New Delhi , India 3 Central Institute of Road Transport, Pune , India 4 Department of Civil Engineering, National Institute of Technology, Tiruchirappalli , India Among the human factors that influence safe driving, visual skills of the driver can be considered fundamental. This study mainly focuses on investigating the effect of visual functions of drivers in India on their road crash involvement. Experiments were conducted to assess vision functions of Indian licensed drivers belonging to various organizations, age groups and driving experience. The test results were further related to the crash involvement histories of drivers through statistical tools. A generalized linear model was developed to ascertain the influence of these traits on propensity of crash involvement. Among the sampled drivers, colour vision, vertical field of vision, depth perception, contrast sensitivity, acuity and phoria were found to influence their crash involvement rates. In India, there are no efficient standards and testing methods to assess the visual capabilities of drivers during their licensing process and this study highlights the need for the same. Keywords: Crash involvement, driver licensing, generalized linear modelling, visual functions. DRIVING typically forms the primary and preferred approach of travel in many countries around the world 1, the ill consequences of which are road crashes. According to the report by the Ministry of Road Transport and Highways, Government of India 2, driver fault forms a significant share of the causes of road accident in India. Figure 1 shows the causal factors of road accidents in India in 2013, along with the percentage share. Human functional failure can be assessed by identifying the limits in human functions that allow a person to adapt to changing situations, for example, experience, visual abilities, risk taking behaviour, etc. With respect to driving, human functional failures can arise from endogenous (inabilities of drivers) and/or exogenous factors (environment which influences endogenous factors) 3. Human functional failures along with their defective interactions with factors such as human, vehicle and environment are the key reasons for road accidents. Human functions with respect to driving primarily include perceptual and/or cognitive performance such as visual performance, auditory skills, bio-mechanical skills, speed judgment and adaption, reaction time, attention, etc They can be broadly classified into two categories physical and psychological. The present work focuses on identifying the relation between visual functions and crash involvement propensity of drivers in India. Physical functions of drivers are important parameters in evaluating their safe driving abilities 7. Vision skills are among the prominent physical functions that assist a driver in perceiving traffic situations. These functions are difficult to quantify and to consider them in road safety evaluation is a difficult task. In heterogeneous and complex traffic conditions commonly witnessed in India, drivers need to remain vigilant throughout, to safely respond to vehicles of different sizes coming their way abruptly from any direction. The complexities further magnify while driving heavy-vehicles. This has caused an increasing number of heavy-vehicle crashes in many Indian cities 8,9. Assessing the influence of visual abilities on crash involvement is essential in identifying the underlying causes of accidents due to driver fault. A simple, multi-disciplinary test comprising of assessment of vision and cognitive tests, hazard perception and change detection tests was found to have a significant capacity to evaluate how safe or unsafe a driver is 10. To assess visual fitness of a driver, visual acuity, contrast sensitivity and peripheral vision form critical components 11. Impairment in visual skills was found to be a significant causal factor for road crashes in drivers above the age of 70 years 12. Several studies have been conducted worldwide to investigate the influence of visual skills on crash propensity. *For correspondence. ( Figure 1. Causes of road accidents in India (2013). CURRENT SCIENCE, VOL. 110, NO. 6, 25 MARCH Drivers with binocular visual acuity are found to have a higher crash risk compared to those with normal vision. In an experiment conducted by Hofstetter 13, persons with binocular visual acuity problems reported double the accident risks compared to those with normal vision. Estimation of effect of binocular vision on road crash distributions of taxi drivers revealed that the average crashes per year were more in drivers with problems in binocular vision 14. Recent research also supports the association of visual impairment and motor vehicle crashes, specifically in older drivers 12. Depth perception plays an essential role in judging the speed of oncoming vehicles while driving. Inabilities in speed judgment may contribute to crash risks 15. Researchers also believe that colour vision and glare recovery strongly associate with poor driving performances 16,17. Protanopia, defined as red green colour blindness, is considered critical in the Australian driver licensing procedure. Since 1994, any person with protanopia is restricted from getting commercial driving licence in Australia. Studies reveal that regardless of severity, protanopia highly influences the risk of road accidents 18. Since many roads in India are undivided, overtaking vehicles often come in conflict with oncoming vehicles from the opposite end. In a road accident investigation study conducted on national highways, it was observed that all the nine head-on collisions observed on undivided highways were mainly due to overtaking vehicles entering into the oncoming vehicle lane 19. Tendency of not maintaining safe stopping sight distance is also a drawback among many Indian drivers, leading to risky situations on Indian roads. In such cases satisfactory depth perception becomes important in ensuring the safety of drivers. Glare can be defined as the sensation caused when bright light is flashed in front of one s eyes, obstructing his/her vision for a couple of seconds. This is a common phenomenon witnessed in night-time driving due to the use of high beam lights. Time taken to recovery from this glare varies in individuals depending on their age and vision conditions. Glare increases reaction time in drivers, thereby influencing their safety in a negative manner 20,21. Again, due to the presence of many undivided roads in India, acceptable glare recovery is important to avoid collisions. In simple terms, contrast sensitivity can be defined as the ability to distinguish between an object from its background. Studies have shown that persons with contrast sensitivity impairment restrict themselves from driving, thereby reducing their annual mileage. This self-regulation is mainly seen due to the increased risk of motor vehicle collisions 22. Also, depth perception of on-coming vehicles is affected by contrast sensitivity Influence of phoria on driving performance was ascertained in the studies conducted by Burg Performance of drivers with central field of vision impairment and normal peripheral vision was evaluated by Lamble et al. 27. It was observed that the reaction time of these drivers was higher compared to those with normal vision. Also, persons with central vision loss had a greater likelihood of involving in night-time crashes 28. Drivers with binocular visual field loss were found to have a higher crash and conviction risk compared to those with normal vision 29. Table 1 summarizes the significance of each of the above-mentioned vision parameters in relation to driving. Vision test is an essential component of commercial driver licensing in the United States. All states in the US have visual acuity requirements for licensure, and all but three have set the minimum best corrected visual acuity (BCVA) requirement at 20/40 in the better eye. Georgia requires a BCVA of at least 20/60 in at least one eye; for New Jersey and Wyoming, the requirement is 20/50. For the 34 states with a binocular horizontal visual field requirement, 15 stipulate 140 ; for the other 19 states, the range is from 105 to 130 ; Maine requires 150. Several states list the horizontal dimension of the visual field of applicants with only one useful eye; this ranges from 55 (Kansas) to 105 (Arkansas). Some states, including North Carolina and Texas, do not issue any driver s licence to a person with homonymous hemianopia (loss of vision in the right half or left half of both eyes). Only Kentucky has a vertical visual field requirement: 25 above and below the fixation point 30. In the United Kingdom, separate vision test standards are followed for private driver licence and commercial driving licence (for bus and lorry drivers) applicants. For private driver licence, a minimum visual acuity of 6/12 for both eyes, as measured in Snellen s chart is required. Also, adequate field of vision that is attested by an ophthalmologist is essential. For bus and lorry drivers, visual acuity of 6/7.5 at least in the best eye and 6/60 in the other is mandated. Horizontal field of vision of 106, with extensions not less than 70 towards left and right and 30 above and below, with no defects in the central field of 30 is also a must 31. Australia also follows separate vision requirements for private diver licence and commercial driving licence. A minimum of 6/12 visual acuity in the better eye or both eyes is essential to avail unconditional private driving licence. Conditional licence is considered for applicants who meet these standards with corrective lenses. For commercial driving licence, a minimum visual acuity of 6/9 in the better eye and 6/18 in the worse eye is required. For applicants with visual acuity worse than 6/24, driver licence is rejected. Horizontal field of vision extending up to 110 and 10 respectively, above and below the horizontal midline is mandatory for private driver licence, whereas for commercial licence it is 140 and 10 respectively, above and below the horizontal midline. Colour vision, except for protanopia, is not a mandatory CURRENT SCIENCE, VOL. 110, NO. 6, 25 MARCH 2016 Table 1. Characteristics of vision skills in relation to traffic situations Characteristics in relation Visual parameters General characteristics to traffic situations Inputs from the literature review Visual acuity Ability to see small details clearly Reading distant traffic signs Defects in visual acuity results in doubled crash risk Colour vision Distinguishing different colours Identification of traffic signals Negatively affects driving performance Phoria Coordination of both eyes to To identify the position of a Affects driving performance correctly identify the vehicle or an obstruction in placement of an object ahead front of the driver correctly Depth perception Judgement of distance between Passing on two-lane road with Defects in depth perception objects oncoming traffic pose serious problems while overtaking Contrast sensitivity Seeing objects in similar Detecting dark-coloured Poor contrast sensitivity brightness as that of colour pedestrians at night increases risk of motor vehicle collision Glare recovery Ability to resist and recover Reduction in visual performance Poor glare recovery from glare due to headlight glares significantly increases reaction time resulting in accident risk Peripheral vision Detection of objects at the Seeing two wheelers Defects in visual field increase sides of the visual fields approaching from sides reaction time of drivers and likelihood of night-time crashes Source: Traffic Engineering Hand Book, Institute of Transportation Engineers, 1999, 5th edn and previous literature. requirement in the Australian driver licensing procedure for private vehicles 32. India follows a single-phase licensing system, which recommends a single phase of driver education and training prior to the written and driving test. Driver education is not mandatory and physical fitness of candidates with respect to visual abilities, hearing, etc. is not evaluated before issuing driver licence. Only the manoeuvring abilities of drivers are considered sufficient for granting the licence 33. Among the above-mentioned visual parameters, acuity is the only parameter evaluated as part of the vision test conducted to issue driving licence in India. According to the Motor Vehicle Act 1988 and Central Motor Vehicles Rules 1989, a self-declaration, medical certificate from a registered medical practitioner is sufficient to qualify in the vision test for driver licence, making the law relaxed. Also, the laws are similar for all, irrespective of age and individual characteristics 5. These lacunae in the present system of driver licensing need immediate attention in order to address road safety issues in India. The standards followed in other countries may not be directly applicable in aptly assessing driver visual capabilities in India. Therefore, there is an inherent need for extensive research focusing on the area of road safety. Considering these issues, the following objectives have been formulated for the present study to emphasize on the importance of vision functions of drivers influencing road crash involvement in India. Evaluating the influence of vision parameters of the drivers on their road crash involvement in India. To identify critical driver vision parameters affecting safe driving ability in Indian conditions. It is evident from the past literature that visual functions are among the crucial physical parameters in relation to safe driving performance. This study attempts to assess the effect of these parameters on crash involvement of Indian drivers. Three hundred and eighty seven Indian drivers belonging to different organizations, age groups and driving experience volunteered for the study. The sample included drivers from the Karnataka State Road Transport Corporation (KSRTC), which is one of the major public transport undertakings in India established in 1961; Bangalore Metropolitan Transport Corporation (BMTC), which is a Government agency that operates the public transport bus service within Bengaluru, India; Vijayanand Roadlines Limited (VRL), which is one of the leading private business groups in road transportation and logistics in Karnataka, India along with some volunteers from Indian Institute of Science (IISc), Bengaluru, and learner licence applicants and licence renewal aspirants at the Road Transport Office (RTO), Yeshwanthpur, Bengaluru. The random sample has been categorized based on age to confirm whether there is reasonable representativeness of the population. Table 2 gives details of sample size with respect to age. CURRENT SCIENCE, VOL. 110, NO. 6, 25 MARCH Table 2. Sampling details Sample Organization Category of vehicle driven/gender Age category (years) Number of drivers Percentage KSRTC Bus drivers/male Total ( = 38.1; = 9.16) BMTC Bus drivers/male Total ( = 42.82; = 8.01) VRL Bus and freight vehicle drivers/male Total ( = 36.9; = 8.64) IISc Private vehicle drivers/male and female Total ( = 37.14; = 12.51) RTO (Learner/driver/renewal licence applicants) private vehicle drivers/male and female Total ( = 31.81; = 11.79) Total sample Total ( = 129; = 44.24) Personal details and road crash histories of tested drivers were obtained from organizational databases. For some samples such as personal vehicle drivers from IISc and RTO, where organizational databases were unavailable, a structured questionnaire was used to collect accident history information from the participants. As drivers participated in the study voluntarily, they were willing to provide data. The data were used to relate the vision test results to the crash involvement tendency of the tested drivers. The collected data included age of the driver, number of years of driving experience and number of crashes he/she has been involved in. Driver vision skills were tested using DVS-GT Deluxe Vision Screener Model # 1158WE instrument. The visual functions tested included visual acuity, colour vision, phoria, night vision, depth perception, contrast sensitivity, glare recovery, peripheral vision and vertical field of vision. Appendix 1 provides the test criteria used to evaluate the drivers. The tested drivers were categorized as acceptable (1) or unacceptable (2) based on test results. The vision evaluation standards adopted in this study are followed worldwide by ophthalmologists for general vision testing and also in the licensing system of some countries (for example: Washington, USA) to screen applicants for driver licence. The data obtained during the study were tabulated and coded for further analysis. Ratio analysis and z-test of the sample were conducted. A generalized linear model (GLM) was developed using univariate analysis of variance (ANOVA) and one-way ANOVA with repeated measures. GLME is an extension of classic linear modelling incorporating response variables that follow any probability distribution in the exponential family 34, initially coined by Nelder and Wedderburn. The explanatory variables in this study (vision test results) were qualitative and of categorical form, whereas the response variables were quantitative (number of crashes). GLM was found to be the most appropriate method for such data types, whose means do not follow normal distribution and instead are multiplicatively related to the explanatory variables 35. CURRENT SCIENCE, VOL. 110, NO. 6, 25 MARCH 2016 Figure 2. Ratio analysis results. The vision test results of all the above-mentioned samples have been summarized and the percentage of road crash involvement of the tested drivers with respect to the vision test results has been obtained from ratio analysis (Figure 2). The vision test results reveal that out of the 160 KSRTC drivers tested, 101 have at least one visual defect, i.e % of the drivers did not satisfy the minimum vision requirements for driving. A simple comparison of the road crash histories of the drivers to the vision test results shows that the crash involvement rates are high (up to 87%) in drivers categorized as unacceptable. The number of BMTC drivers involved in road crashes with unacceptable vision standards is high (58.3%) when compared to those with acceptable visual standards. Among 50 drivers tested from VRL, 50% qualified the required standards, whereas the other 50% failed in at least one of the tested vision parameters. Fifty-six volunteers (both male and female) from IISc, including professors, research students and administrative staff were tested for vision. It is important to note that the crash histories of these tested subjects were obtained from selfreports. The vision test results and the road crash details showed that the drivers with visual defects were involved in a relatively higher number of road crashes compared to those with normal vision. Forty-three learning licence/ driver licence/licence renewal applicants from the RTO at Yeshwanthpur, were also tested as a part of the study. Twenty-seven of them qualified with acceptable visual standards, while 16 did not. Significant number of road crashes of novice drivers was observed in this sample group, although they do not have a permit to ride. Leniency of the present licensing system and traffic law enforcement methods in India are depicted in these cases. Table 3 shows the cumulative test results of the entire sample of 387 drivers
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