A statistical comparison between severe accidents and PDO accidents in Riyadh A.S. Al-Ghamdi College of Engineering, King Sand University,

Transcription

1 A statistical comparison between severe accidents and PDO accidents in Riyadh A.S. Al-Ghamdi College of Engineering, King Sand University, sa Abstract Riyadh, capital of the Kingdom of Saudi Arabia, is a fast developing and modernized city. With a population of three million inhabitants and a motorized rate (population per vehicle) of 3.8, Riyadh has been experiencing increasing traffic accident problems. Official statistics have shown that more than 400 fatalities and 3000 injuries occur annually due to traffic accidents. The severity index of traffic accidents over the past four years is higher than the corresponding nationwide index. This study aims at investigating the severity of traffic accidents in Riyadh. An attempt was made to compare property damage only (PDO) accidents with severe accidents in order to analyze the nature of severe accidents and determine their characteristics so that some remedies can be recommended. For achieving this purpose, a total of 1774 police-reported accidents was collected in a systematic random manner for the period of 1996 through Analysis using various test statistics was conducted to compare the two categories of accidents. The study found that improper driving behavior is the primary cause of accidents in Riyadh and the young drivers are most often the victims in such accidents. In addition, the taxis and pick-up trucks are in high risk of being involved in accidents. The analysis indicates that there is an urgent need for reviewing existing public awareness programs and law enforcement strategies. 1 Introduction Riyadh, capital of the Kingdom of Saudi Arabia, is a fast developing and modernized city. With a population of three million inhabitants and a motorized rate (population per vehicle) of 3.8, Riyadh has been

2 448 Urban Transport and the Environment for the 21st Century experiencing increasing traffic accident problems. Official statistics show that more than 400 fatalities and 3000 injuries occur annually due to traffic accidents/ The death rate (death per 100,000 population) in Riyadh is greater than that of large cities in the USA (cities with over 1000,000 population, such as Phoenix, Los Angeles, Chicago, Detroit, New ork, Philadelphia, Dallas, and Houston). The National Highway Safety Council reported that the death rate, on average, in those cities was 9.1 in 1993/ The corresponding rate in Riyadh is 13.3 indicating that traffic accidents are more severe in Riyadh. When compared with countrywide accidents, accident severity in Riyadh has been higher over the past few year, as illustrated in Figure 1. This figure indicates that the severity index (fatality per all victims (fatality + injury)) has been somewhat uniform for the country. The points of the citywide index were below the countrywide index points until 1995, when surprisingly, a remarkable change took place. Since 1994 the curve representing Riyadh has exceeded the countrywide data. This indicates that traffic accident severity has increased significantly during the last four years. Unfortunately, there is no objective explanation for this sudden significant problem. Even from the Riyadh Traffic Department (RTD) no explanation was found. It should be mentioned that in United States^ and Sweden^ severity indices were and 0.026, respectively. Thus, Riyadh is suffering from severe accidents. This study aims at investigating the severity of traffic accidents in Riyadh. The goal of the study was not to examine the dramatic change in the severity index, shown in Figure 1, yet, an attempt was made to compare property damage only (PDO) accidents with sever accidents (accidents end with a personal injury and/or fatality) in order to analyze the nature of severe accidents and determine their characteristics so that some remedies can be recommended. 2 Data Collection The accident data used in the analysis were extracted from the manual filing system in The Riyadh Traffic Department (RTD). A great deal of effort was made to obtain data from the police records. A total of 1774 police-reported accident reports were collected in a systematic random manner for the period of 1996 through The sampled accidents were divided into two sub-samples. Thefirstone includes 651 severe-accident reports.the other sub-sample consists of 1123 property-damage-only (PDO) accident reports (reported when damage exceeds an estimated value

3 Urban Transport and the Environment for the 21st Century 449 of $130). In addition, copies of the accident reports were obtained for more details about the accidents. Unfortunately, most of the reports were incomplete, that is, about 60% of the details were missing. The police officer responsible for completing the report usually recorded information, like the time, location, cause, and type of accident. Some other important information, such as light and road-service conditions is not filled out. Even the exact location of accident is not identified properly. Rather, the name of the road is written along with the type of location (e.g., intersection). The drawing of the accident is somewhat helpful in figuring out more details about the location and the accident itself. 55, M 0 T3 1 v 1 1 C in 1U ~/ ^* ~ *^^ ear + Riyadh KSA Figure 1: Severity index of Riyadh and countrywide. After reviewing and checking for completeness, the data available in each accident report was extracted, coded, and then entered into an EXCEL spread sheet. A database wasfinallydeveloped for all the coded data. The areas of data classification include: Accident category (severe or PDO). Accident characteristics (e.g., location, cause, and collision type). Accident result (number and age of injuries and fatalities). Persons involved (driver, passenger, and pedestrian). Driver characteristics (age, nationality, and driving license status). Vehicle class (passenger car, pick-up truck, taxi). 3 Preliminary Analysis In this part, several characteristics of PDO accidents and severe accidents were compared. After classifying the data and obtaining proportions, as

4 450 Urban Transport and the Environment for the 21st Century presented in Table 1, a pairwise comparison for proportions at each class was conducted using the z-test* For the accident characteristics listed in the table, only two proportions (accidents involving vehicles and rightangle accidents) are not statistically significant (account for 9% of all proportions) indicating that, overall, the severe accidents and PDOs in the study sample have different characteristics. Even for the two similar characteristics, the difference between proportions is not substantial. 3.1 Accident Location: It is obvious, from Table 1, that most of the severe and PDO accidents occur at road sections (nonintersection sites) followed by intersectionrelated accidents and median-opening-related accidents. More than 55% of severe accidents and one-third of PDO accidents occurred at nonintersection sites. Severe accidents at median openings account for one third of those for PDOs. One-fifth of PDO accidents occurred at median openings indicating that these locations are problematic. In Riyadh, this type of opening permits vehicles to make cross and turning movements, but in doing so they encroach on adjacent lanes and usually do not have a protected space clear of other traffic. According to RTD and Riyadh Municipality officials, no design justifications and warrants such as traffic volume, speed limit, type of turning vehicles, and geometry are considered when constructing such locations in some of the divided roads. Also, no traffic control signs (i.e., yield sign, stop signs, or traffic signals) are used to regulate the various movements. 3.2 Accident Type While collision with other vehicles ranks at the top of other types of PDO accidents, pedestrian accidents, representing one-half of all accidents, come at the top of the list for severe accidents (49.8%) followed by collision among vehicles and fixed-object accidents (Table 1). The overturn accidents in the severe category account for three times that of PDO accidents. The pedestrian accidents represent about one half of severe accidents indicating that pedestrians in Riyadh are dangerously exposed to vehicles in the traffic stream.

5 Urban Transport and the Environment for the 21st Century 451 Transactions on the Built Environment vol 33, 1998 WIT Press, ISSN Table 1. Proportions of the classifications of both categories of accidents. Description Distribution by Location Nonintersection Intersection Median opening Ramp Circle Undefined Distribution by Accident Type Vehicle Fixed object Overturn Pedestrian Distribution by Collision Type Right angle Rear-end Sidewipe Head-on Other Distribution by Cause Speed too fast Run red light Failing to yield Followed too closely Wrong way Other Note: = es, N = No. 3.3 Collision Type Proportion (%) Severe ace PDO ace Significant at 5% level N N It should be noted from Table 1 that the majority of accidents in the severe category involve vehicles (e.g., in right-angle, head-on, and sidewipe collisions). More than two-thirds (69.6%) of severe accidents are of head-on type andright-angletype. On the other hand, just less than twothirds (63%) of PDO accidents are ofright-angletype and rear-end type. Although the proportion of right-angle collisions in severe accidents is not

6 452 Urban Transport and the Environment for the 21st Century significantly different from that in PDO accident, the proportion of headon collisions in severe accidents is almost four times that in PDO accidents indicating that the chance of being hurt in head on collision is greater than that inright-angleone. 3.4 Cause of Accident Over-speeding ranks as the first cause of severe accidents in Riyadh because it is the first cause of road accident/ This result is not surprising because it has been shown in past research that the higher the speed the greater severity of accident/ Even though it is not at the top of the causes for PDO accidents, driving over the speed limit accounts for about onefourth (23.6%) of such accidents, which is second after "Failed to yield". Figure 2 shows the percentages of the two categories of accidents distributed by cause of accident. From the figure it can be seen that speed ranks first followed by wrong way (W Way) and failing to yield (F) as major causes for sever accidents. On the other hand, the major causes for PDO accidents are failing to yield, exceeding speed limits, and driving too closely (DTC). Exceeding the speed limit comes at the top of the list in severe accidents and second in the PDO accidents indicating that many drivers in Riyadh do not obey the speed limit sign. This result is consistent with what another study which indicated that at some urban sites the percent of drivers going over the speed limit was 90%.* More than one-half of fatal collisions (52.5%) and about one-half of injury collisions (45.9%) result from speeding and disregarding red light. It is also clear that speeding-related violations, i.e. exceeding speed limit and driving too closely, account for about 40% in each categories of accidents. The corresponding percent in the USA is 18% less than half of that in Riyadh/ Another study showed that 50% to 95% of drivers, depending on the road class, violate the speed limit on Riyadh roads.* Recent statistics in Norway indicate that 30% to 80% of motorists, depending on the type of road, violate speed limits? Similarly, these percents range between 36 and 49 on urban roads in Sweden/

7 Urban Transport and the Environment for the 21st Century 453 E3 Severe Ace. H PDO Ace. Speed RRLight W Way FT Cause of acciden DTC Figure 2. Percentages of severe and PDO accident. accidents based on cause of 4 Distribution of Victims by Age The victims in the sever accidents are distributed by age as shown in Table 2. The percentages show the loss of youth in traffic accidents. It is clear that most of the victims are below 35 years. That is, 58.3% and 62.1% of the fatalities and injures, respectively, are below the age of 35. Children constitute about afifthof fatalities (18.3%) and more than afifth (22.4%) of the injuries indicating the relatively high risk of children in a severe accident in Riyadh. Table 2. Distribution of fatalities and injuries by age. Age Group < >50 Unknown Fatality % Injury Table 3 shows that the majority of drivers involved in both severe and PDO accidents are thirty years an younger. About onefifthof drivers

8 454 Urban Transport and the Environment for the 21st Century involved in PDO accidents are of age eighteen years or less, yet, the percentage of the drivers in this group in severe accidents is 32.5% (about one-third). This result indicates that young drivers are involved in more severe accidents. The traffic rules in KSA require a person applying for a driving license to be at least 18 years of age. Some drivers of 17 years and below 18 can obtain a temporary permit. Among those below 18 years and involved in severe accidents, more than one third (35.1%) are less than 17 years and with no legal status of driving, as presented in Table 4. This helps clarify the problem of under-age driving in Riyadh. Figure 3 illustrates the distribution of those young drivers involved in severe accidents at "exact" age. The figure again emphasizes the problem of illegal driving. Note that those drivers reported in accidents but there are many who drive under age and have not yet been involved in an accident. Table3. Distribution of drivers by age in the two accident categories. Age Group < >50 Unknown % of drivers Severe PDO Table 4. Drivers below age of 18 and involved in severe accidents. Age Group (year) Less than 18 Less than 17 %

9 Urban Transport and the Environment for the 21st Century Age Figure 3. oung drivers involved in severe accidents. 5 Risk Index for Type of Vehicle The driver risk for various accident-related groups is represented by the concept of Risk Index (RI) and obtained using the following relationship: percent accident involvement in group percent population in group Among other statistical measures in traffic safety studies, this index has been used in risk analyses for different driver groups concerning categorical data such as age, sex, nationality, etc. In this study, this index was used for type of vehicle, in this section, and driver nationality in the next section below. The percentage of passenger-car involvement in PDO accidents reached in this study is 68.8% whereas the percentage of passenger-car vehicles in the vehicle mix in Riyadh is estimated at 61.69%.* Thus, the risk index (RI) for the passenger-car group is Table 5 presents risk indices for the three classes of vehicles in Riyadh. It is obvious that all groups, especially pick-up truck and taxi groups are involved in disproportionate numbers of accidents relative to their proportions of the vehicle population. It is also noticed from the table that among the three groups, pickup truck drivers followed by taxi driver have a four-fold and double chance of being involved in sever accidents. This indicates that there is an urgent need to investigate drivers of the two groups in order to determine

10 456 Urban Transport and the Environment for the 21st Century the causes and implement appropriate remedies. Table 5. Risk index for a vehicle class. Vehicle Class Passenger car Pick-up truck Taxi Severityi Index Severe PDO Distribution of Drivers by Nationality Table 6 presents the distribution of drivers by nationality in both categories of accidents. Relative to their proportion in the country's population, non-saudi drivers are at higher risk of being involved in either PDO or severe accidents as shown in Table 7. That is, the risk index for this group of drivers are higher in both categories of accidents. Table 6. Distribution of drivers by nationality. Severe PDO Total Saudi Non- Saudi Total Table 7. Risk index for a driver nationality. Driver Nationality Saudi Non-Saudi Severity Index Severe PDO Discussions and Recommendations A major difficulty facing safety research in Saudi Arabia is the dilemma of data collection. Manual search is the only way of obtaining accident

11 Urban Transport and the Environment for the 21st Century 457 records from the source, namely, traffic police. Details also need to be extracted manually from each record. Most of the details in the accident report are missing, incomplete, or unclear. Computerization of accident data filling is a primary need. This will not only help in conducting research but also in the decision-making process for safety improvements. It is obvious from the analysis that there is a high accident frequency at median openings indicating that these locations are problematic and a remedy is needed. Engineering warrants should be established for providing such locations. About 50% of severe accidents involved a pedestrian indicating the need for protecting pedestrians in Riyadh. It would be of interest to have a future study to analyze this type of accidents to alleviate this problem. The analysis of accident causes in this study indicated that improper behavior is the cause of the majority of traffic accidents in Riyadh. In other words, human error is the major cause of such accidents. Speeding, failing to yield, and disregarding red light account for more than half of all accident causes in Riyadh. Thus, most of traffic accidents in Riyadh are driver-behavior related. This result indicates that traditional police enforcement is insufficient to ensure compliance with speed limits and other traffic rules. There is a need for improved enforcement and possibly the introduction of automated speed enforcement. Results of this study support findings of previous research that the human loss in the young groups in traffic accidents is substantial. More than half of fatalities and injuries sampled in this study were below the age of 35 years indicating that this developing country is loosing many of its youth in traffic accidents. This result suggests the need for educational programs and campaigns among the young population. The analysis revealed that illegal-age driving appears to be problematic. This conclusion raises the question about the effectiveness of law enforcement in keeping such drivers off the road. Although the citizen drivers consists of the higher percentage in the driving population, the study provides evidence that non-saudi drivers are more likely to be involved in traffic accidents than Saudi drivers. A review for the process of driving license exams should be done to have those drivers adjust to the driving environment in Riyadh. Some of those drivers might need a special training program before getting behind the wheel. Taxi drivers and pick-up drivers are found to be more at risk of being involved in either PDO or severe accidents. These two groups are involved in disproportionate number of accidents relative to their proportion of the vehicle population. They should not be given a license

12 458 Urban Transport and the Environment for the 21st Century until they have demonstrated the ability to drive safely. In summary, the findings of this research suggest that there is an urgent need to evaluate the existing public awareness programs and the law enforcement strategies implemented by traffic police in Riyadh. Improper driving behavior can be reduced through well-designed educational campaigns as well as strict law enforcement. References [1] Traffic Accident Statistics. Annual Statistics for the period Ministry of Interior, Riyadh. [2] Accident Facts. National Safety Council, 1994 & 1995 Editions, USA. [3] RTSR (1996 Road Traffic Safety Report). The Swedish National Road Administration, Sweden, [4] Devore, J. L. Probability & Statistics for Engineering and the Sciences. Brooks/Cole Publishing Company, Wadsworth, Ic., Belmont, California, [5] Solomon, D. Accidents on Main Rural Highway Related to Speed, Driver and Vehicle. Bureau of Public Roads, Washington, D. C, 1964 [6] Al-Ghamdi, Ali S. Spot Speed Analysis on Urban Roads in Riyadh. Accepted for publication at Transportation Research Record, TRB, National Research Council, Washington, DC, [7] Elvik, R. Effects on Accidents of Automatic Speed Enforcement in Norway. Transportation Research Record No. 1595, Transportation Research Board (TRB), National Research Council, Washington, DC, pp , [8] McShane, W. R, androess, R. P. Traffic Engineering. Prenctice Hall Polytechnic Series in Transportation, New Jersey, [9] MOP. Center Plane-2. Ministry of Planning, The National Transport Study, Riyadh, 1996.