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Bloody routes

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Bloody routes

  1. 1. Bloody Routes By Mona Khafagy, MSc., P.E. Highway and Transportation Expert Research and Teaching Associate American University in Cairo 2016
  2. 2. Effect of Defects in Road Geometric Elements on Accident Rates Contents Carriageway Horizontal Curve Vertical Curve Combined Horizontal and Vertical Curves Shoulders and Medians Conclusion
  3. 3. CAUSES OF ACCIDENTS The Handbook of Highway Engineering, Australia,2006  Surface Condition  Road Geometry Road Side Features Road Risk Factors First edition of AASHTO Highway Safety Manual was published in 2010.
  4. 4. Geometric Design Elements Number of Lanes (Lane) Lane Width (Foot/m) Surface Condition (Good/Bad) Grade on Tangent (%) Grade on Curve (%) Sight Distance (Feet/m) Radius of curve Degree of curvature Superelevation Shoulder Width (Foot/m) Surface Condition (Good/Bad) Traffic Control Delineator (Yes or No) Lighting (Yes or No) Guide Sign (Yes or No) Marking (Yes or No) Median Median Width (Foot/m) Vertical Curve AlignmentHorizontal Curve Alignment Roadway/ Carriageway
  5. 5. Carriageway Characteristics AASHTO Recommends • High 1.5 to 2 % (0.015 ft/ft, m/m) • Intermediate 1.5 to 3 % Cross Slope describes the slope of a roadway perpendicular to the centerline. If a road were completely level, water would drain off it very slowly As carriageway width increases, traffic accidents decreaseSafest Road is a Divided, Multi-lane Road with full control of access. The level of safety decreases on three-lane roads, there is enough space available for wrong maneuvers and dangerous overtaking Basic Definitions AASHTO Recommends lane widths between 2.7 to 3.6 m ( 9 – 12 ft) for safety and comfort of driving. Lane width should not be less than 2.7 m (9ft) and used only on low volume ruler roads
  6. 6. 2) Poorly Designed Shoulders 42.8% of the fatal collisions reported on highways occurred on two-lane rural highways.(17) 1) Passing Maneuver Blind Angles 3) Lights from Opposing Direction Carriageway Characteristics (Con.)Source of Risk Why Two Way-Two Lanes Roads are more Dangerous??
  7. 7. Every 1% increase in cross-slope results in approximately 32% increase in rollover crash risk. (3) 20% of truck-involved loss- of-control crashes and it is likely the Road Cross-sectional Geometry have played a part in many of these.(3) Rollover Crashes 50 % of the severe crashes were rollovers where an HGV (heavy good vehicles) occupant died. (13) 66% of rollover crashes occurs while cornering. (3) Rollover Crashes are more hazardous than other types of crashes. Carriageway Characteristics (Con.)Source of Risk How Defects in Cross Slope Affect Accident !!!!
  8. 8. Widening of Carriageway Heavy Vehicle Crash Risk could be REDUCED BY 8% PER METER OF WIDENING . in New Zealand (3) 0.25 meters of widening results in Reduction in Crash Rate By 2% To 2.5% (3) Widening Lanes from 2.7 to 3.7 m would reduce crash by 31%. (4) Widening lanes or shoulders on curves can reduce curve accidents by as 33 % (12) Segments with Three Lanes are 40% less in crash risk than two-lane segments (6) Carriageway Characteristics (Con.)How to improve!
  9. 9. Horizontal Curves The premier factor in accidents inside horizontal curves is RADIUS. As The Number of Horizontal Curves per km increases, the total number of accidents decreases (1) Drivers Underestimate The Severity of The Horizontal Curvature.(4) Accident Severity on Curves is Higher Than Those Occurring on Straight Roads (6) Accidents increase when; Radius is decreased level of curvature is increased (1) Accident rate on radii less than 100 m is Four Times Higher than those with curve radii of 500 m or higher.(5) Basic Definitions That is when
  10. 10. Accident Rates in Road Curves are about 1.5 To 4 Times Higher than in Straight Roads (6) Left-turn curves have higher accident rate than right- turn on right hand traffic systems.(5)  A unit increase in Degree of Curvature is associated with a 5% Decrease in the crash risk (6) On horizontal curves, stopping sight distance is limited and there is a high probability of skidding  Curve flattening is expected to reduce accidents by up to 80 percent, depending on the amount of flattening. (12)  Adding spiral 'transitions on curves was associated with a 5% accident reduction.(12) Approximately 60%to 66% of all crashes occurring in horizontal curves are single-vehicle loss-of-control crashes (off-road crashes).(16) Horizontal Curve (Con.)Source of Risk How to improve!
  11. 11. SuperElevation Superelevation: is the amount of "banking“ of the curve.(9) The most common cause to truck rollovers is the difficulty for the driver to assess the combination of Speed, Position of CoG (center of gravity) and the Cornering Maneuver. Basic Analysis of Cornering Force Establish the dynamic equilibrium for steady cornering, aiming for minimizing steering effort, weight transfer, tyre wall deformation and tyre contact patch distortion.(13) Horizontal Curve (Con.) Basic Definitions Superelevation Deficiency (SD): the difference between the actual Superelevation at a curve and that prescribed in the American Design Guidelines – the AASHTO Green Book.(5) Source of Risk
  12. 12. SuperElevation  Superelevation deficiency of 4% results in a 4% increase in accident risk. (3)  Improving deficient superelevation can reduce accidents by approximately 10%.(12)  An improvement of 2% in Superelevation (i.e., increasing Superelevation from 3% to 5% to meet AASHTO design guidelines) would be expected to yield an accident reduction of 10 to 11%.(12) Super-elevation should not exceed 8%. (6) Horizontal Curve (Con.) How to improve!
  13. 13. The most important risk factors for rollover are high CoG, high speed, cargo displacement, bad road conditions, driver behavior (13) Heavy truck on bad Superelevation (13) A adjustment of 1 % in super-elevation could result in a 5 % reduction in heavy vehicle loss- of-control crash risk while cornering.(13) Run-Off- the-road accidents were significantly influenced by Superelevation error.(11) Superelevation Horizontal Curve (Con.) How to improve! Source of Risk Rollover Crashes on Horizontal Curve
  14. 14. How to Improve Safety on Horizontal Curves?  Reconstruct the curve to make it less sharp  Widening lanes and shoulders on curves  Adding spiral transition to curves  Increasing the amount of Superelevation (when needed)  Increase the clear roadside recovery distance by reallocating utility poles and trees  Assure adequate surface drainage  Provide increased surface skid resistance on combined horizontal and downgrade vertical curves Horizontal Curve (Con.)
  15. 15. Vertical Curve Crest Curve: Stopping Sight Distance Governs The Design Sag Curve: Height of Headlight Beam Governs The Design Vertical Grade Increases, Accident Rate Increases AASHTO indicates that For overall safety, a sag vertical curve should be long enough that the light beam distance is nearly the same as the stopping sight distance. 7 feet 100 feet Basic Definitions
  16. 16. Grades of 2.5 to 4% deviation from designed grade increase crashes by 10% and 20% respectively. (4)(15) Accident Rate on down grades is slightly higher than that on upgrades.(5) A sharp increase in accident rate on downgrades greater than 4 % .(5) Overtaking on upgrades of two lane roads be an additional hazard.(7) Crash frequency increases with gradient percent.(16) Vertical Curve (Con.) Source of Risk
  17. 17. On sections with high gradient, safety problems may occur from speed differentials between passenger cars and heavy vehicles (e.g. heavy vehicles idling on upgrade sections), as well as vehicles braking on downhill sections (e.g. increases in braking distances and possibility of heavy vehicle brake overheating). (16) Climbing Lanes on rural two-lane roads reduced the total accident rate by an average of 25%. (15) A Climbing Lane is an extra lane in the upgrade direction for use by heavy vehicles whose speeds are significantly reduced by the grade Vertical Curve (Con.) Source of Risk How to improve!
  18. 18. Combined Horizontal and Vertical Curve The coincidence of a horizontal and a crest vertical curve: 1) Lead to significant limitation of the available sight distance 2) Prevent the prompt perception of the curve 3) Create a false impression of the degree of curvature. (16) The Deviation from the combined curves AASHTO specifications had fatal rollover crashes about 15 times as frequently. (9) Numbers of accidents are high at points where high-slope sections end in low-radius horizontal curves. (1)
  19. 19. Combined Horizontal and Vertical Curve (Con.) An inefficient combination of horizontal and vertical alignment may lead to road safety problems, even when the horizontal and the vertical alignment are separately correct and according to guidelines. Poor coordination of horizontal and vertical alignments can create locations where the available sight distance drops below the required sight distance (16)
  20. 20.  Paved/Unpaved (earth, turf, gravel)  Graded and usable width depends on foreslope and rounding  Consider function, safety, and capacity impacts  Slope  2 to 6% (paved)  4 to 6% (gravel)  8% (turf)  Min. 2% + lane slope  Max crossover 8%]  Width 0.6 – 3.6 m (2 – 12 ft) Shoulder Characteristics Basic Definitions
  21. 21. Shoulder Characteristics As width is increased, the number of accidents are decreased Shoulder Elevation Change may be the result of an irregularity in the road surface, or where the vehicle’s wheels drop off the roadway onto a soft shoulder or grass berm. 20 to 25 % of rollover crashes fall into this category. (3) Larger accident rates are exhibited on un-stabilized shoulders, including loose gravel, crushed stone, raw earth or turf, than on stabilized or paved shoulders. (8) Source of Risk
  22. 22. Shoulder Characteristics (Con.) 21% reduction of total accidents was determined on road with shoulders of 0.9 m-2.7 m compared to road without shoulders. (15) One foot widening results in a reduction of signal-vehicle accidents by 8.8%. (15) How to improve!
  23. 23. Median Presence of a median on a highway contributes positively to road safety Medians designed at a lower altitude than the pavement are better for safety than medians designed at a higher altitude.(1) Median works as division for traffic in opposite directions and a recovery area for out-of-control vehicles. (6)
  24. 24. Median Characteristics (Con.) The type of the median barrier is also an important aspect The fact that an obstacle is placed within the roadway environment that provides a target for collisions can lead to an increased number of crashes. [39] Different Types (especially concrete) have the potential to increase crashes. [22] Since Studies have shown that The presence of a barrier will result in a reduction of cross-median type crashes but it also has the potential to increase median-related crashes. (15) Median Barrier Safety shape barriers are designed to mitigate the energy of crash impacts
  25. 25. CONCLUSION  Road improvements are always feasible  While designing carriageway, Generosity in not always welcomed.  Geometric defects and Pavement condition should be included in accident investigation forms.  Improvements don’t have to be expensive.
  26. 26. references 1. “Analysis of Relationship Between HighwaySafety and Road Geometric Design Elements: Turkish Case” A.F. Iyinama, S. Iyinama, and M. Ergun, Technical University of Istanbul, Faculty of Civil Engineering, 34469 Istanbul, Turkey. 2. “Changes in Geometric Design Standards on Interurban Undivided Roads” Dr D. O’Cinneide, Traffic Research Unit, Department of Civil and Environmental Engineering, University College Cork, Ireland,2010 . 3. “The Effect of Cross-Sectional Geometry on Heavy Vehicle Performance and Safety”, Paul Milliken and John de Pont, TERNZ Ltd, Transfund New Zealand Research Report No. 263, 2004. 4. “Effective safety factors on horizontal curves of two-lane highways”, Ali Aram , et.al., journal of Applied science, Asian network for scientific information, 2010. 5. “INFLUENCE OF ROAD CHARACTERISTICS ON TRAFFIC SAFETY”, Sarbaz Othman, Robert Thomson, Chalmers University of Technology, Department of Applied Mechanics, Sweden. 6. “Risk Assessment Review” Author Dr Tim McCarthy, NUIM, Ireland, 2011. 7. “Road Grade and Safety” E. Hauer., April 17, 2001. 8. The effect of ruler road geometry on safety in southern africa, christo J.Bester, Joster A.Makunje, University of stellenbosch, minisrty of works in Malawi. 9. “Safety Effectiveness of Highway Design Features, ALIGNMENT”, Charles V. Zegeer, P.E. James M. Twomey, P.E. Max L. Heckman, P.E. John C. Hayward, Ph.D., P.E., Federal Highway Administration Design Concepts Research Division, HSR-20, February 21, 2012. 10. “THE EFFECT OF SPEED, FLOW, AND GEOMETRIC CHARACTERISTICS ON CRASH RATES FOR DIFFERENT TYPES OF VIRGINIA HIGHWAYS”, Nicholas J. Garber, Ph.D. Professor of Civil Engineering and Faculty Research Engineer Angela A. Ehrhart Graduate Research Assistant, January 2000. 11. An evaluation of altenative horizontal curve design approaches for ruler two-lane highways”, research report 04690-3, texas transportation institute, the texas a&M university system college station, texas, 1996. 12. “COST EFFECTIVE GEOMETRIC IMPROVEMENTS FOR SAFETY UPGRADING OF HORIZONTAL CURVES” , Volume I. Final Report, C. Zegeer, University of North Carolina Highway Safety Research Center, 1990. 13. “LOWERED CRASH RISK WITH BANKED CURVES DESIGNED FOR HEAVY TRUCKS” , MSc. Johan Granlund, et.al., WSP, Sweden, 2014. 14. “STUDYING THE EFFECT OF SPIRAL CURVES AND INTERSECTION ANGLE ON THE ACCIDENT RATES ON TWO-LANE RURAL HIGHWAYS IN IRAN” , MOHAMMAD SAEED MONAJJEM, Ph.D. K.N.Toosi University of Technology, Faculty of Civil Engineering Tehran,Tehran, Iran, 2013. 15. THE INFLUENCE OF ROAD GEOMETRIC DESIGN ELEMENTS ON HIGHWAY SAFETY, HameedAswad Mohammed, Civil Engineering Department – Anbar University- Iraq, 2013. 16. “Roads”, Project co-financed by the European Commission Directorate General for Mobility & Transport , 2013

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