Road safety depends on humans, vehicles, and highway conditions. These factors influence road safety separately or in combination. Despite these facts, the police report indicated that only a single cause of accident ha s been reported for a given accident in Ethiopia and the number of accidents that had been caused by road defect accounted around 1% of total accidents per year, which underestimates its contribution to road accidents. Beside these facts, only a few studies were carried out in Ethiopia on this issue. Even though dangerous road segments were identified and ranked along the same study area of this paper in our previous publication, Hawassa-Shashemene-Bulbula two-lane rural highway, the influence s of road geometric parameters on road safety w ere not correlated along this study area. Therefore, it is imperative to clarify the relationship between the expected number of traffic accidents and the geometric conditions of the road under study to reduce accidents and provide safe driving environment. The main objective of this study was to quantify the influence of road geometric parameters on road safety. Using historical accident data, traffic data, and road data , the expected number s of accidents w ere estimated by using the empirical Bayes (EB) method. Then, the expected number s of accidents ha ve been correlated with one or more road geometric parameters at a time. Accordingly, the identified dangerous road segments in the previous publication (DOI: 10.4236/jtts.2018.83009) were further analyzed to estimate the influence of road geometric parameters on road safety based on expected accident frequency. The result of the analysis shows that the radius of horizontal curve, superelevation, transition curve length, lane and shoulder widths were negatively correlated with the expected frequencies of accidents. Whereas the number s of horizontal and vertical curves per segment, grade of the road, the occurrence of left turn horizontal curves with down grade and right turn horizontal curves with upgrade were positively correlated with the expected number of accidents. Therefore, it has been concluded that the influence of road geometry has significant effect on the occurrence of accidents along this study area.
KeywordsRoad Geometric ParametersExpected Number of Accidents
Haddon, W. (1972) A Logistic Framework for Categorizing Highway Safety Phenomena and Activity. The Journal of Trauma, 12, 193-207. https://doi.org/10.1097/00005373-197203000-00002
American Association of State Highway and Transportation Officials (AASSHTO) (2009) Highway Safety Manual. AASSHTO, Washington DC.
Berhanu, G. (2000) Effects of Road and Traffic Factors on Road Safety in Ethiopia. Ph.D. Thesis, NorwegianUniversity of Science and Technology, Trodhium, Norway.
Abebe, M.T. and Belayneh, M.Z. (2018) Identifying and Ranking Dangerous Road Segments A Case of Hawassa-Shashemene-Bulbula Two-Lane Two-Way Rural Highway, Ethiopia. Journal of Transportation Technologies, 8, 151-174. https://doi.org/10.4236/jtts.2018.83009
Elvik, R. and Vaa, T. (2004) The Handbook of Road Safety Measures. Elsevier Science, Amsterdam.
Aram, A. (2010) Effective Safety Factors on Horizontal Curves of Two-Lane Highways. Journal of Applied Sciences, 10, 2814-2822. https://doi.org/10.3923/jas.2010.2814.2822
Karimi, A. and Kashi, E. (2018) Investigating the Effect of Geometric Parameters Influencing Safety Promotion and Accident Reduction (Case Study: Bojnurd-Golestan National Park Road). Cogent Engineering, 5, Article ID: 1525812.
Hameed, M. (2013) The Influence of Road Geometric Design Elements on Highway Safety. International Journal of Civil Engineering and Technology, 4, 146-162.
Bauer, K.M. and Harwood, D.W. (2013) Safety Effects of Horizontal Curve and Grade Combinations on Rural Two-Lane Highways. Transportation Research Record, 2398, 37-49. https://doi.org/10.3141/2398-05
European Road Safety Observatory (2006) Road Safety Management. http://www.erso.eu/
Hauer, E. (1999) Safety and the Choice of Degree of Curve. Transportation Research Record, 1665, 22-27. https://doi.org/10.3141/1665-04
Department of Transportation (2007) Safety Handbook for Secondary Roads, USA.
Stewart, D. and Chudworty, C.J. (1990) A Remedy for Accidents at Bends. Traffic Engineering and Control, 31, 88-93.
Brenac, T. and Annex, I. (1994) Curves on Two-Lane Roads, Safety Effects of Road Design Standards. SWOV, Leidschendam, the Netherlands.
Kanellaidis, G. (1991) Aspects of Highway Super-Elevation Design. ASCE Journal of Transportation Engineering, 117, No 2. https://doi.org/10.1061/(ASCE)0733-947X(1991)117:6(624)
Harwood, D.W., Council, F.M., Hauer, E., Hughes, W.E. and Vogt, A. (2000) Prediction of the Expected Safety Performance of Rural Two-Lane Highways. Paper No. FHWA-Rd-99-207, Federal Highway Administration, Washington DC.
Hauer, E. (2000) Safety of Horizontal Curves, Review of Literature forthe Interactive Highway Safety Design Model. http://www.roadsafetyresearch.com/
Matthews, L.R.and Barnes, J.W. (1988) Relation between Road Environment and Curve Accidents. Proceedings of 14th ARRB Conference, Canberra, 28 August-2 September 1988, 105-120.
Obaidat, M.T. and Ramadan, T.M. (2012) Traffic Accidents at Hazardous Locations of Urban Roads. Jordan Journal of Civil Engineering, 6, 436-447.
Hassan, Y., Sayed, T. and Bidulka, S. (2002) Influence of Vertical Alignment on Horizontal Curve Perception: Phase II, Modelling Perceived Radius. Transportation Research Record, 1796, 24-34. https://doi.org/10.3141/1796-03
Institution of Highways and Transportation (IHT) (1990) Guidelines for Accident Reduction and Prevention. International Edition, London.
Smith, B. and Lamm, R. (1993) Coordination of Horizontal and Vertical Alignment with Regard to Highway Aesthetics. Transportation Research Record Journal of the Transportation Research Board, 1445, 73-85.
Kiran, B.N., Kumaraswamy, N. and Sashidhar, C. (2017) A Review of Road Crash Prediction Models for Developed Countries. American Journal of Traffic and Transportation Engineering, 2, 10-25.
Jerry, P., John, S., Wendel, R. and Dominique, L. (2009) Impact of Shoulder Width and Median Width on Safety. NCHRP Report 633. Transportation Research Board of the National Academies, Washington DC.
Transportation Research Board (1987) Designing Safer Roads, Special Report 214. Transportation Research Board, Washington DC, 319.
Landge, V.S., Jain, S.S. and Parida, M. (2006) Modeling Traffic Accidents on Two Lane Rural Highways under Mixed Traffic Conditions. 87th Annual Meeting of Transportation Research Board.
Hauer, E. (1997) Observational before-after Studies in Road Safety: Estimating the Effect of Highway and Traffic Engineering Measures on Road Safety. Pergamon, Oxford, 289 p.
Shen, J. and Gan, A. (2003) Development of Crash Reduction Factors: Methods, Problems, and Research Needs. Transportation Research Record: Journal of the Transportation Research Board, 1840, 50-56. https://doi.org/10.3141/1840-06
Huang, H., Chin, H. and Haque, M. (2009) Empirical Evaluation of Alternative Approaches in Identifying Crash Hot Spots Naive Ranking, Empirical Bayes, and Full Bayes Methods. Transportation Research Record, 2103, 32-41. https://doi.org/10.3141/2103-05
Xie, K., Ozbay, K., Yang, H. and Yang, D. (2018) A New Methodology for Before-After Safety Assessment Using Survival Analysis and Longitudinal Data. Risk Analysis, 39, 1342-1357. https://doi.org/10.1111/risa.13251
Hauer, E., Harwood, D.W., Council, F.M. and Griffith, M.S. (2002) Estimating Safety by the Empirical Bayes Method: A Tutorial. Transportation Research Record: Journal of the Research Board, 1784, 126-131. https://doi.org/10.3141/1784-16
Brimley, B.K. (2011) Calibration of the Highway Safety Manual Safety Performance Function and Development of Jurisdiction Specific Models for Rural Two-Lane Two-Way Roads in Utah. All Theses and Dissertations, 2611. https://scholarsarchive.byu.edu/etd/2611
Persaud, B., Lyon, C. and Nguyen, T. (1999) Empirical Bayes Procedure for Ranking Sites for Safety Investigation by Potential for Safety Improvement. Transportation Research Record: Journal of the Research Board, 1665, 7-12. https://doi.org/10.3141/1665-02
United Nations (2017) World Population Prospects: The 2017 Revision. United Nations Department of Economic and Social Affairs, Population Division. https://Esa.Un.Org
Africa::Ethiopia—The World Factbook-Central Intelligence ...-Cia. https://www.cia.gov/library/publications/the-world-factbook/geos/print_et.html
Saffarzadeh, M. and Shabani, S. (2007) An Accident Forecasting Model for Horizontal Curves in Intercity Roads. Journal of Transportation Research, 4, 9-a-50.