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Traffic safety at roundabouts in Urban Areas - Case Study in Jordan

Researches & Papers, Civil Engineering


The main objectives of this research were to investigate traffic accidents problem at roundabouts in Jordan, and to explore possible relationships between traffic accidents and traffic, geometric and planning variables. Thirty roundabouts were selected from different cities as a case study. Traffic and geometric variables were measured through field survey. The results indicated that vehicle-vehicle accidents constitute the major portion of accidents pattern (94.2%). The analysis showed that roundabouts with three or four legs resulted in lower accidents rate than roundabouts with five legs. Traffic accidents at roundabouts were found strongly correlated with peak-hour volume, land-use type and presence of traffic calming measures. The correlation coefficients between geometric variables and traffic accidents were found relatively small. The developed statistical regression models can be used by traffic engineers to assess the impact of implementation of roundabouts on reducing traffic accidents at intersections


Roundabout is a form of intersection at which traffic moves around a central island in one direction. Also, they can be defined as small raised island placed in the middle of an intersection. They are typically landscaped with ground cover and street trees. Roundabouts require drivers to slow to a speed that allows them to comfortably maneuver around them. Roundabouts are widely used in Europe, Australia, Arabic countries, and recently they received more acceptances in the United States and other countries. They are used to reduce conflicts points at intersections, accidents severity, traffic speeds, traffic delay, air pollution, fuel consumption, and construction costs. Although roundabouts work better than traffic signals at intersections with low to medium traffic volumes, they require large spaces, which may cause confusion for drivers who are not familiar with roundabouts capacities. (Arndt 1998) investigated the relationship between geometry and accident rates on 100 roundabouts in Queensland. His accident prediction models included estimated speed variables, which interestingly, were found to be more significant than traffic volumes. Approach curvature, central island diameter, and separation between legs were all found to have a major impact on accident rates. Harper and Dunn 2003) developed more advanced prediction models that enable more accurate evaluation of urban roundabout accidents. These models were developed to predict vehicle accidents on urban roundabouts in relation to traffic volumes and geometric variables. They found that entering and circulating accidents are the most common crash type. (Haycock and Hall 1984) found that at 4-arm roundabouts in the UK, the risk of single vehicle accidents increased with wider entries and with greater entry path curvature, but decreased where there was greater approach curvature. In Jordan, roundabouts are widely used in urban and suburban areas, not only at low or medium traffic volumes but also at high volume of traffic. Although, traffic accidents problem is growing and becoming more serious over the years, safety experience at roundabouts is not well documented. According to the statistics of (Jordan Traffic Institute 2004), it was found that 70,266 traffic accidents occurred during the year of 2004, which have resulted in 818 fatalities, 2451 sever injuries and 14,276 slight injuries. Roundabouts involved during the same year in 663 traffic accidents (0.94% of total traffic accidents and 17% of traffic accidents at intersections) with one fatality, 34 slight injuries and 2 sever injuries. In Jordan, safety performance at roundabouts is not well documented, efforts were concentrated on evaluating capacities and delay at roundabouts. (Al-Masaied and Fedda 1998) developed an empirical model for the geometric effect on capacities of 10 roundabouts in Jordan. They found that the estimated entry capacity is mainly influenced by entry width and island diameter. In addition, (Al-Omari, Al-Masaied, and Al-shawabkah 2004) used an empirical approach to develop delay models. They found that geometric variables have significant effect on roundabout entry delay. The entry width had the greatest influence over other variables such as circulating lane width and roundabouts diameter. Performance of roundabouts and the relationship between accidents and traffic and geometric factors need further investigation in Jordan. The main objectives of this research effort were to: 1. Explore possible relationship between traffic accidents and traffic, geometric and planning characteristics of roundabouts in Jordan based upon the available accident data. 2. Develop regression models that can be used to predict traffic accidents at roundabouts in urban areas.


The main objectives of this study were to investigate the safety performance of roundabouts in Jordan and to explore possible relationships between traffic accidents and traffic, geometric and planning characteristics of Roundabouts. To accomplish these objectives, data on traffic accidents for three years (2003-2005) were obtained from traffic departments and data on traffic, geometric and planning characteristics were measured through field surveys for 30 roundabouts in Jordan. Based on linear regression analysis, two prediction models were developed using accidents rate and number of accidents as dependent variables. Based on the analysis in this study, the following points were concluded:  The majority of roundabouts accidents resulted in property damage only (92.87%), (7.09%) and (0.04%) of accidents were injury and fatality accidents, respectively.  Vehicle-vehicle accidents had a significant proportion of the total accidents (94.21%).  Not giving priority for circulating vehicles was found the most common driver`s fault (58.78%), and was greater than other common faults: following too closely, wrong stopping, and not giving priority for pedestrians.  Roundabouts with three or four legs resulted in lower accidents rate and number than roundabouts with five legs.  Presence of humps, pedestrian's crossing and other traffic calming measures at roundabouts had strong impact on reducing both the traffic accidents rate and accidents number.  The peak hour volume and the average entry width have significant effect on safety at roundabouts. Based on the previous findings, the following recommendations can be stated:  Improving safety at urban roundabouts requires consideration of driver behavior, pedestrian behavior, roadway characteristics and land use planning.  More attention should be given to pedestrian safety at roundabouts by providing traffic calming measures according to the standards and clearly mark the crosswalk at each entry.  It is recommended to use entry angle of (30º- 60º) range for design purposes.  More comprehensive well-documented accidents reports that include detailed data on all approaches of roundabouts are necessary to improve the predictability of traffic safety models


Turki Al-Suleiman (Obaidat) Prof. of Civil Engineering Fatin Abu Al-Bandoura Graduate Research Assistant Hashem Al-Masaeid Prof. of Civil Engineering Jordan University of Science & Technology P.O. Box 3030 – Irbid- 22110-Jordan

Comparison between Post Tension and Hollow Core Slabs systems (Case Study) - Commercial Building in Amman

Researches & Papers, Civil Engineering


How to select the most viable structural floor slab system ? Post Tension or Hollow Core Slabs systems?


Using current standard, design for each system were determined and then advantages and disadvantages for each system were analysed. Two systems were then compared to determine which system would most benefit the construction and design of the Commercial Building. The study has been carried out considering all the requirements of the local building authorities, Amman Municipality and governing relevant codes as listed later in this report. Our study focus on changing the floor slab system, vertical elements and foundations were kept as original design.


From this comparison, it was concluded that while two systems achieve Safety in Design & Construction; The Post Tension Slab outstands in Constructability, Floor Clear Height and Layout Flexibility however Hollow Core Slabs outstands in Building Weight and Lead Time. Cost is variable and almost equal for both systems


Ali Alsheikh