Roadside Design Guardrail Design Licking County Engineer s Office April 16, 2014
Roadside Design
National Roadside Fatalities (Most Harmful Event) Other 20% Trees 50% Barriers 8% Utility Embankment and Ditches 9% Poles 13%
Design Options In Order of Preference 1. Remove the obstacle 2. Redesign the obstacle so that t it can be safely traversed 3. Relocate the obstacle to a location where it is less likely to be struck 4. Make the obstacle breakaway 5. Shield the hazard with longitudinal barrier 6. Delineate the obstacle
Possible vs. Practical The Roadside Should Be Made As Safe as Practical
Barrier Warrants
EMBANKMENT WARRANT
Crash Testing Safety performance of fbarrier designs can be shown through standardized testing. Full scale crash testing is the standard method used.
Crash Testing Some criteria for passing a crash test: to determine if barrier is capable of containing the vehicle (structural test) if occupant deceleration and ride-down velocities are survivable (occupant test) no debris penetrating the vehicle or deforming the passenger compartment vehicle remains stable, it does not roll nor redirected back into traffic
MASH-08 Update Criteria Test Vehicle Specifications - Small car increases from 1,800# to 2,420#. - Pickup truck increases from 4,400# to 5,000#. - TL-4 truck increases from 18,000# to 22,000#. - No longer use vehicles older than 6 years.
Semi-Rigid Barriers Strong Post, Blocked-out W-Beam guardrail (ODOT Type 5) W-Beam rail with 6 3 post spacing, offset blocks, in strong soil.
W-Beam Guardrail SCD GR-2.1
W-Beam Guardrail Components: W-beam rail 12 ½ feet long Wood or steel posts usually 6 feet long Wood or plastic blockouts Soil support
W-Beam Guardrail Purpose of the: Rail - provides tension to capture and redirect vehicles Post hold the rail at the appropriate p height and absorb impact energy Blockout keep vehicle wheel from catching the post Soil provides resistance to the posts
W-Beam Guardrail Various blockout shapes
Roadside Design Guardrail Placement
Length of Need A guardrail must extend in front of a hazard to protect vehicles leaving the road in advance of the hazard.
Length of Need
Guardrail Deflection Once barrier is warranted and needed, the deflection distance may dictate t the type of barrier (flexible, semi-rigid, or rigid) to install. ODOT uses 5' 6 for w-beam guardrail.
Guardrail Deflection Type 5A guardrail has a post spacing of 3-1.5
Type 5 Guardrail 27 Tall Guardrail determined NOT crashworthy y( (too short) 29 Acceptable per NCHRP 350 Too Short
Guardrail Height 29 inches to top of rail +/- 1 10:11 shoulder slope
Post Embedment Posts resist impacts if installed deep h tto h t enough have soilil support
Maintain Rail height Reduce wheel snag potential
Post Embedment 9 ft. long posts should be specified at locations where the distance from the face of the barrier to the slope break point is less than 2 ft. (L&D 906) 6 ft. post everywhere else unless specified.
MGS with a MASH truck
Type 5 (27 ¾ ) with a MASH truck
Roadside Design Guardrail Anchors
Anchors Standard Construction Drawings GR-4.1 Type A Anchor GR-4.2 Type T Anchor
Anchors Guardrail works best if impact energy is allowed to be transferred both downstream and upstream through rail elements by utilizing the tensile capabilities of the w-beam material.
Anchors In a crash near the guardrail end, the anchor holds the guardrail in tension. The anchor prevents the rail from flapping and allowing the vehicle to go through.
Type A Turned-down ends are anchors. Previously considered crash worthy, but now limited to lower speed and lower volume roads.
SCD GR-4.1
Type A The Type A anchor assembly used as an approach or trailing guardrail end treatment in any of the following situations (L&D 603.3.4): On non-nhs arterials, collectors and local roads with a design year ADT of 4000 or less. On any roadway outside the clear zone. On any non-nhs roadway with a design speed of less than 50 mph.
Type T
Can Cause Terrible R lt
Type T The Type T anchor assembly may be used on any roadway in any of the following situations (L&D 603.3.5): On trailing ends of guardrail runs on multi-lane lane roadways, where located outside the clear zone of opposing traffic. In guardrail runs where directional changes are made using a radius of less than 25 ft. (see L&D Figures 603-3 and 603-4). On the ends of guardrail runs on drive approaches (see L&D Figure 603-3).
Type T
Intersections It is often difficult to protect di driveways or side roads: Sharply pycurved guardrail has not passed crash testing, because of the high angles of impact Angles can almost be 90 degrees, which usually exceeds the strength of the steel rail If it does capture the vehicle, blunt head-on crash forces usually exceeds occupant survivability
Intersections Typical driveway treatment.
Intersections Typical driveway treatment at a bridge.
Sometimes You Just Get Lucky
Sometimes You Just Get Lucky
Sometimes You Just Get Lucky
Questions???