Design of curves and their adjacent elements presents the greatest safety problem on rural two-lane roads. The use of the existing alignment consistency safety criteria (design, operating speed, and driving dynamic consistency) could have some shortcomings, especially in countries where the project or design speed is in use instead of (higher) operating speed. The consequence is that the designer should use smaller cross fall on curves than needed, while the calculated side friction is lower than in reality. Further, the existing graphs of adjacent curve radii do not take into account that there is a maximum operating speed achieved for a certain radius or long tangent above which it does not increase. This paper presents a methodology for determination of adjacent horizontal curve radii, with and without tangent between, based on the operating speed models which include dependence of operating speeds on tangents and curves on speed of adjacent alignment elements as well as maximum tangent and curve speed. The developed graphs of adjacent radii at the same time include the limiting values of driving dynamic consistency criteria, so the road designer does not need to calculate permissible and demand side friction for every combination of adjacent alignment elements.
Lamm R, Psarianos B, Choueiri, E. M, Soilemezoglou, G. A Practical Safety Approach to Highway Geometric Design International Case Studies: Germany, Greece, Lebanon, and the United States. Proc. of the International Symposium on Highway Geometric Design Practices, 30 Aug. – 1 Sep. 1995, Boston, MA, USA; 1995. p. 1-9. Available from: http://onlinepubs.trb.org/Onlinepubs/circulars/ec003/ch9.pdf
Lamm R, Choueriri EM, Mailaender T. Traffic Safety on Two Continents-a ten-year Analysis of Human and Vehicular Involments. Proccedings SHRP, Goutenberg, Sweden; 1992. p. 18-20.
Raff MS. Interstate Highway Accident Study. Highway Research Board Bulletin 74: Traffic Accident Studies. Washington D.C.; 1953. p. 18-45. Available from: http://onlinepubs.trb.org/Onlinepubs/hrbbulletin/74/74-003.pdf
PIARC Technical Committee on Road Safety. Road Safety Manual. World Road Association; 2003. 602 p. Available from: https://roadsafety.piarc.org/en
ERA-NET ROAD. Safety at the Heart of Road Design. Final Report of the ERA-NET programme, 2012.
Torbic DJ, Harwood DW, Gilmore DK, Pfefer R, Neuman TR, Slack KL, Hardy KK. Guidance for Implementation of the AASHTO Strategic Highway Safety Plan: A Guide for Reducing Collisions on Horizontal Curves. NCHRP Report 500 Series, Vol. 7, Transportation Research Board, Washington, D.C., 2004. Available from: doi:10.17226/13545
Baldwin DM. The Relation of Highway Design to Traffic Accident Experience. AASHTO, Convention Group Meeting, Washington, DC; 1946.
Krammes RA, et al. Horizontal Alignment Design Consistency for Rural Two-lane Highways. Report no. FHWARD-94-034, FHWA, Washington D.C., 1995. Available from: https://rosap.ntl.bts.gov/view/dot/740/dot_740_DS1.pdf?
Pravilnik o osnovnim uvjetima kojima javne ceste izvan naselja i njihovi elementi moraju udovoljavati sa stajališta sigurnosti prometa. NN 110/2001. Available from: https://narodne-novine.nn.hr/clanci/sluzbeni/2001_12_110_1829.html
Modeling Operating Speed. Washington DC: TRB; 2011. Available from: http://onlinepubs.trb.org/onlinepubs/circulars/ec151.pdf
Chowdhury MA, Warren DL, Bissell H. Analysis of Advisory Speed Setting Criteria. Public Roads. 1991;55(3):65-71.
McLean JR. Speeds, Friction Factors and Alignment Design Standards. Australian Road Research; 1988.
Die Richtlinien für die Anlage von Straßen – Teil: Linienführung (kurz RAS-L), Germany, edition 1973, 1985, 1995.
Choueiri EM, Lamm R, Kloeckner JH. Safety Aspects of Individual Design Elements and their Interactins on Two-lane Highways: International Perspective. Transportation Research Record. 1994;1445: 34-46. Available from: http://onlinepubs.trb.org/Onlinepubs/trr/1994/1445/1445-004.pdf
Ottesen J, Krammes RA. Speed-Profile Model for a Design Consistency Evaluation Procedure in the United States. Transportation Research Record. 2000;1701: 76-85. Available from: doi:10.3141/1701-10
Fitzpatrick K, et al. Alternative design consistency rating methods for two-lane rural highways. Washington: Federal Highway Administration. Report No. FHWARD-99-172. 2000b.
Polus A, Fitzpatrick K, Fambro DB. Predicting operating speed on tangent sections of two lane rural highways. Transportation Research Record. 2000;1737: 50-57. Available from: doi:10.3141/1737-07
Cvitanić D, Maljković B. Operating speed models of two-lane rural state roads developed on continuous speed dana. Tehnički vjesnik. 2017;24(6): 1915-1921. Available from: doi:10.17559/TV-20150304133437
Fitzpatrick K, et al. Design Speed, Operating Speed, and Posted Speed Practices. NCHRP, report 504, 2003. Available from: http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_rpt_504.pdf
Said D, Hassan Y, Abd El Halim AO. Comfort thresholds for horizontal curve design. Canadian Journal of Civil Engineering. 2009;36(9): 1391-1402. Available from: doi:10.1139/L09-075
A Policy on Geometric Design of Highways and Streets. American Association of State Highway and Transportation Officials (AASHTO); 2004.
Forschungsgesellschaft für Straßen-und Verkehrswesen. Richtlinien R 1 für die Anlage von Landstraßen. Köln, Germany: FGSV Verlag GmbH; 2012.