The roadside

1. The roadside Hossein Naraghi CE 590 Special Topics Safety March 2003 Time spent:12 hrs

2. The roadside • The forgiving roadside • Collision with roadside objects account for 25-30 percent of fatal crashes • Significant in both urban and rural environments • Measures to address this problem • Reducing crash frequency • Shoulder treatment • Speed control • Combating driver fatigue • Combating alcohol abuse

3. The forgiving roadside (continued) • Reducing crash severities • Forgiving roadside • Develop cost-effective ways to reduce severity of run-off-road crashes • There are two strategies • Roadside clear zone • If a vehicle leaves the roadway, it is less likely to strike a roadside object • Impractical in many cases • Roadside hazard management program

4. Roadside clear zones • Recovery area • The zone beside the road which let driver to be able to regain the control of the vehicle • If it has not struck a fixed object • If it has not rolled over • The distance vehicles travel along the roadside and the distance which it penetrates into the roadside

5. Roadside clear zones (continued) • Depends on • Vehicle traveling speed • The angle vehicle leaves the roadway • Early studies in US established that with flat sides slopes • 80-85% of vehicles traveling at highway speeds could recover within 30 ft from the edge of the roadway • This distance was considerably greater • On curves • On steeper slopes

6. Roadside clear zones (continued) • Clear zone • An area within the recovery area which is ideally kept free of roadside hazard • Roadside hazards • Poles, trees, and shrubs with trunks greater than 4 inches • Culvert end walls • Steep batters (greater than about 6:1 or ideally 4:1) • drains

7. Roadside clear zones (continued) • Anything that pose a danger to errant vehicles • Any obstacles within the zone should either be removed or shielded with guard fencing • An area which reflects the the probability of crashes occurring on that road • The cost-effectiveness of providing such a zone

8. Roadside clear zones (continued) • The clear zone dependent upon • Traffic speed • Roadside geometry • Traffic volume • It is a compromise between safety, economic and in many cases environmental consideration • If it is not practicable to provide width of clear zone, alternative remedial treatment such as guard fencing can be considered

9. Roadside clear zones (continued) • The clear zone is measured from the edge of the traffic lane. • “For curves with radius of less than 600 m (2,000 ft), the clear zone width on the outside of the curve should be doubled” • In low speed environment of urban area, a clear zone of not less than 1 m wide may be accepted to achieve the balance between safety and aesthetic

10. Roadside clear zones (continued) • Cross section • Flatter roadside slope have a significant effect on single vehicle crashes • Crash rates fall steadily as side slopes are flattened from 3:1 to 7:1 or flatter • Little crash reduction is expected by flattening from a 2:1 to 3:1 slope • Side slopes of 5:1 or flatter are needed (Zegeer and Council, 1992)

11. Roadside clear zones (continued) • Clear zones and side slopes are closely related • Clear zone must include a flat traversable slope of 4:1 or flatter (Crillo 1993) • Slopes steeper than 4:1 are too steep to allow recovery of control • Vehicles encroaching on such slopes can be expected to travel all the way to the bottom if not rollover

12. Roadside clear zones (continued) • Establishing and maintaining an obstacle free clear zone has definite safety benefits • It appears to be cost-effective on rural roads even at low traffic volumes • For volumes greater than 4000 vpd and speed around 62 mph a clear zone of 30 ft is required • Side slopes need to be flatter than 5:1 to significantly reduce the probability of rollovers

13. Roadside hazard management • Where it is not possible to provide roadside clear zone • Impractical • Too expensive • Roadside hazards present some measure of risk to • Errant vehicles • Pedestrians at risk from such vehicles

14. Roadside hazard management (continued) • The objective of roadside hazard management program is to keep this risk to a manageable level • With mass action programs, there is scope for a pro-active approach • It is required to identify the features associated with crashes of a given type, and then treat in priority order all sites which exhibit those features (Ogden and Howie 1990)

15. Roadside hazard management (continued) • A hierarchy of treatments of fixed roadside hazards have proposed • Eliminate all obstacles from the roadside, either by good design and technology for new facilities, or removal or relocation of all existing obstacles • If it is not possible to eliminate all roadside objects • Identify those most likely to be struck, establish priorities, and organize removal or relocating

16. Roadside hazard management (continued) • Make those objects most likely to be struck but impossible to remove harmless • Use a safety barrier or shield those obstacles impossible to remove or relocate • Typical treatments • Relocation of rigid utility poles, under grounding of cables, or replacement with frangible poles

17. Roadside hazard management (continued) • Enhancing the safety of bridges and culverts by providing • Guard fencing • Bridge railing • Improved delineation • Flattening of batters or installation of guard fencing on steep or high embankments • Shielding the trees with guard fence or removing them from the clear zone • Removal of culvert headwalls or extension of culverts to increase recovery area

18. Roadside hazard management (continued) • Replacing the old guard fencing which does not meet the current standards • Enhance delineation • Roadside devices • Pavement markings • The key component of any roadside management program is maintenance • Training of maintenance personnel is critical since proper installation and ongoing maintenance of many of these treatments is critical to their effectiveness

19. Utility poles • Even though utility poles are present in a significant number of crashes involving fixed roadside objects, not every pole represents a hazard • In general the hazard increase with • Traffic flow • Pole density (poles per length of the road) • Offset from the edge of the road • Greater for poles outside the horizontal curves • Greater at sites with low pavement friction

20. Utility poles (continued) • Treatment of hazardous poles • Relocation of the pole to a safer location • Locating light poles on the inside rather than outside of a horizontal curve • Shielding of poles with safety barriers • Guard fence • Impact attenuator • Use of slip base poles which break away at the base when impacted • Special electrical connections to ensure electrical safety

21. Utility poles (continued) • Do not retard the impacting vehicle and may give rise to secondary crashes especially in area with high concentration of pedestrians or on narrow medians • Use of impact absorbing poles • Especially effective for area with high pedestrians activity • High friction pavements where the pole is on a curve • As a last and least satisfactory resort, attaching reflective delineators to the pole

22. Trees • The most difficult aspect of roadside hazard management concerns tree • Trees can be helpful in shielding headlights and providing a visual barrier between the road and abutting property • Trees add to the aesthetic of the road • Trees can also form an important subliminal delineation function • Substantial trees close to roadway result in hazard

23. Trees (continued) • Removing trees is highly effective • On hazardous location in rural areas • High volume traffic with high speed • Close to the roadway • On the outside of horizontal curve • Low pavement friction • Zegeer and Council (1992) quote a US study which suggest that • Clearing trees to provide an additional 3 ft of recovery space could reduce crashes by 22% • Additional 15 ft of recovery space reduce crashes by 71%

24. Road signs • All road signs should have a frangible post unless located behind a safety barrier • Large signs such as advanced direction signs should be of a frangible design • When struck the supporting post shears and the vehicle passes beneath it • Installation of such posts is very important • Bolts must be correctly tensioned to ensure that they will shear • The base section must not be too low • Allowing debris to accumulate and impede break away • The base section also must not be too high • It can snag an impacting vehicle

25. Road signs (continued) • Frangible designs are not suitable for use in low speed areas where vehicle does not have sufficient speed to satisfactory clear the falling pole • Roundabouts • Smaller, lighter signs mounted on lightweight posts are more appropriate for low speed areas • Lightweight posts made of light gauge steel pipe or channel section which easily deform on impact • applicable to smaller road signs such as warning signs, regulatory signs and chevrons

26. Bridges and culverts • Hazards associates with bridges can be significant • Narrow bridges • increase the probability of vehicle colliding with bridge • Reduce the opportunity for safe recovery • Bridges are over-represented in crashes relative to their length of road system • Bridge crashes are more severe than crashes as a whole

27. Bridges and culverts (continued) • Culverts can be hazard problem • Culvert end wall or pipe end often located quite close to the roadway • Culvert end wall can become less hazardous by being design to match the slop of embankment • Can be replaced with a grated inlet structure • Can be extended so the end wall is further from the roadway

28. Bridges and culverts (continued) • Ogden and Howie (1990) produced guidelines for treatment of bridge sites based on bridge width, traffic flow, and bridge length • Install guideposts and reflective post-mounted delineators when street lighting not present • Install bridge width markers on or adjacent to bridge end post, piers, or abutments on both the left and right side of roadway

29. Bridges and culverts (continued) • Provide edge lining with raised reflective pavement markers where bridge width marker installed to facilitate good lane control • When bridge is on or adjacent to a curve with radius of less than 2000 ft install chevron signs on the outside of the curve • Install the guard fencing according to current standards if warranted • Upgrade the installation of guard fencing with current standards for bridges with existed guardrail

30. Other roadside hazards • Devices aim to protect pedestrians and bicycle facilities can potentially conflict with some of roadside safety principles • Where there are very large pedestrian flows solid bollards may be erected at curb line to protect pedestrians from errant vehicles • This is in conflict with forgiving roadside objectives • There is clearly a tradeoff between the safety of vulnerable road users and the safety of motorists

31. Other roadside hazards • When the roadside object is necessary to protect vulnerable road users, those features should be as safe as possible • Horizontal rails which can spear an errant vehicle should be avoided • Vertical elements should be used • Less hazardous to motorists • More difficult for pedestrians to climb and walk on the roadway • Avoid to install hazardous features which have nothing to do with traffic • Features for Landscaping purposes

32. Safety barriers • Safety barriers include • Guard fences • Flexible • Cable barriers • Rigid • Concrete barriers • Semi-rigid • Steel W-beam barriers • Box beam barriers • Crash cushions • Bridge barriers

33. Safety barriers (continued) • Warrant and guidelines for the installation of guard fencing • On embankments • Slope and height exceed certain values • In US H/V of 3:1 and less and height of 5 m or more Figure 12.12 page 288 • Near roadside hazards • Any hazard within 30 ft of roadside may justify shielding

34. Safety barriers (continued) • On narrow medians • To prevent head-on crashes • Where flow exceed 5000 vpd • Where road formation narrows • At some bridges and culverts • On the outside of sub-standard curves • Where differences between 85 percentile speeds and advisory speed is greater than 10 mph • To protect structures and pedestrians

35. Steel guard railing • Steel guard railing • commonly of a rolled W-section • Rectangular hollow section • Acts by resolving kinetic energy possessed by an impacting vehicle into components in three dimensions • Vertical • Parallel to the rail • Perpendicular to the rail

36. Steel guard railing (continued) • The perpendicular and vertical components must be reduced or dissipated to redirect the vehicle effectively • The energy dissipation is accomplished through bending and crushing of various parts of vehicle and guard rail installation, including the soil • In order to be effective guard railing must installed to allow the energy dissipation to occur

37. Steel guard railing (continued) • The important point to stress is correct installation • The final product must be safer than an unprotected roadside object • Incorrect installation impose a greater hazard than the object it is shielding so the barrier can be ineffective or even counter-productive • Training program for people who make decision about guard rail program and people who install them is an important element of safety barrier program

38. Existing barriers • Decision regarding acceptance, removal, modification or replacement of barrier based • Assessment of the performance of particular installation concerned • Significance of the departure from current practice • Other factors to consider in assessment • Potential hazard of the barrier in compare to hazard it shielded or compare that with a modern barrier

39. Existing barriers (continued) • Suitability of barriers post-spacing, terminals and transitions • Barrier length, alignment, clearance and location relative to adjacent lane • Barrier height • Condition of the roadside between barrier and traffic lane • Alignment of the adjacent roadway

40. Existing barriers (continued) • Examples of deficient guard rails • Guard rail too low • Vehicle may roll over the device • Guard rail too high • Vehicle may pass or trapped beneath the guard rail • Exposed, unanchored fish tail guard rail • Exposed end constitutes a hazard in itself • Result in the guard rail being demolished in a collision rather than decelerating and redirecting the vehicle

41. Existing barriers (continued) • Guard rail with inadequate taper • Correctly tapered guard rail should have its end well away from the pavement • Guard rail with inadequate post spacing • On the approach to a bridge or rigid object • Post spacing should decrease near the bridge end post • Will stiffen the transition between guard rail and bridge • There is a need to inspect the existing guard rail and upgrading them to conform with requirements of current practice

42. Concrete barriers • Concrete barriers • Commonly Known as New Jersey barrier • primarily used for median barriers on divided roads • Warrants are in place to provide directions for the use of this treatment • Represent a significant hazard to errant vehicles in all but very shallow angle collisions

43. Concrete barriers (continued) • Advantages • Intend to prevent or minimize damage to vehicles during low-angle impacts • Does not defect to any appreciable degree, even under sever impacts • Negligible maintenance costs • Vehicles with low center of gravity are subject to roll over in collision with such a barrier • Modify section with a constant side slope may reduce the incidence of roll over

44. Cable barriers • Cable barriers • Flexible barriers less common than rigid and semi-rigid barriers • Cost-effective • in low to moderate traffic flows • In situation where roadside or median design can accommodate the large deflection inherent in these types of barrier

45. Median barriers • Median barriers • Warranted on situation of high flow and narrow median width • Effective in reducing head-on crashes on divided roads but may increase other kinds of crashes • A study of their installation in UK found • 15% reduction in fatalities • Little change in injury crashes • PDO crashes increased by 14%

46. Bridge barriers • Bridge barriers • Design to prevent a light vehicle running of the edge of a bridge • Railings designed to retain heavy vehicles are heavier and more expensive • Warranted in exceptional situations with extreme crash consequences • Barriers on old bridges which do not meet the current standards may present a hazard • Old bridges with timber rails can lead to spearing crashes • Replacing or modification of the railing may be an appropriate treatment • Integrating the bridge railing and the approach guard railing to provide a continuous rail

47. Crash cushions • Crash cushions • Design to absorb some of the kinetic energy of errant vehicle before it impacts the object • Are effective at the end of longitudinal safety barriers in • Medians and freeway gore areas • Bridge piers in narrow medians • End of concrete barrier wall • Toll plazas • Use readily available materials • Sand or water filled barrels

48. Safety barriers and heavy vehicles • Heavier vehicle requires a stronger installation to restrain it • Higher center of gravity is more susceptible to rollover • Barriers for heavy trucks only justified at special locations • Encroachment of large truck could be catastrophic • Bridges adjacent to a school or apartment building • Near a petrochemical plant • Barriers to withstanding vehicles more than 9 ton are only warranted where traffic flow exceeds 100,000 vpd

49. Shoulder treatment • Two major aspects of shoulders relate to • shoulder sealing • Pavement age drops • Paved shoulders are much safer than unpaved shoulders on rural roads • Reduce • run-off-the –road crashes • Head-on crashes • Chance of losing control due to loose material of unpaved shoulders • By providing a grater recovery and maneuvering space

50. Shoulder treatment (continued) • A number of studies examined the safety benefit of paved shoulders • In an Australian study, Armour (1984), found that road with paved shoulders • 60-70 percent lower fatal crashes than road with unpaved shoulders • Benefit was greater on road section with curves or grades • Ogden (1993) in an study of Australian rural roads which had been treated with sealed shoulders as part of a maintenance program • With paved shoulder of 2-4 ft he found such a treatment lowered crash rate by 43% on vehicle km basis