Appurtenances

1. Appurtenances HDM Ch. 10

2. Kinetic Energy (g-forces) • A car weighs 3000 pounds • At 20 mph KE=40,000 ft-lb (0.5mv2) • At 40 mph KE=160,000 ft-lb • If the car above stops in 50 ft • Average deceleration in g’s is 1.07 for a car starting at 40 mph

3. Equations • Kinetic Energy = 0.5*Mass*V2 • Avg Deceleration (in g’s) for a car at some initial speed decelerating to a stopping condition over some length L: • V2/(2*g*L)

4. Appurtenances When vehicles leave the roadway how can you reduce the # and severity of accidents?

5. Clear Zone Area free of hazardous objects and gently graded to permit reasonably safe re-entry to the highway or provide adequate distance for stopping References: AASHTO Green Book AASHTO Roadside Design Guide

6. New & Reconstructed • Provide satisfactory clear zones when practical and provide barriers if not • Clear zone includes: -Shoulder -Recoverable slope (or traversable slope and clear runout width)

7. Clear Zone Based on: • Design Speed • Traffic Volume • Roadside Slope • Curvature of the Road

8. Basic Recovery Width (BRW) Basic width of recovery area that should be provided (see Table 10-1) BRW does not consider curvature, non-recoverable slopes or accident history

10. Non-Recoverable Slope Slope at which it is unlikely a driver will be able to regain control of a vehicle and return to the roadway (vehicle will continue to the bottom of the slope) Embankment slopes steeper than 1:4 are considered non-recoverable Traversable, non-recoverable slopes can be present in the clear zone, but do not count towards the BRW

11. Curve-Corrected Recovery Width (CCRW) Takes into account effects of horizontal curvature Obtain by multiplying BRW by the horizontal curve correction factor found in Table 10-2 Apply factor when long tangents are followed by a curve rated 15 km/hr less than the operating tangent speed

13. Clear Runout Width (CRW) Width provided at the toe of a traversable, non-recoverable fill slope Minimum width should be 2.5 m (why that #?)

14. Desired Minimum Clear Zone Width Larger of: • BRW • CCRW • Sum of CCRW plus the width from the traveled way to the toe of the traversable but non-recoverable slope

15. Design Clear Zone Width Should be at least the minimum and preferably greater than the minimum

16. Point of Need Fixed object • use 15-deg divergence angle • use 10-deg on freeways/interstates

18. Deflection Distance Distance that the outside face line of a barrier will deflect when struck by a vehicle See Table 10-3 (based on 100km/hr; 2000 kg vehicle, 25 deg angle) Deflection distance behind barriers must be kept free of FO’s

20. Barrier Types • Cable Guide Rail • Corrugated Metal (W-beam) (1.5*cable) • Box Beam (3*cable) • Concrete (10*cable)

24. Median Barriers • Designed to withstand impact from either side • Corrugated metal beam • Box Beam • Concrete

25. Selecting Guide Rail • Choose barrier w/ largest acceptable deflection • Deflection must be less than distance from barrier line to nearest hazard that can’t be removed or relocated • Maintain area behind guide railing • (tree dia. > 100 mm is considered a hazard) • Deflections must stay within ROW

26. Potential Hazards • Potential fatalities: • Cliff • Deep body of water • Flammable liquids tank • Fixed Objects: • Bridge piers/abutments • Trees (>100mm) • Utility Poles • Buildings • Retaining Walls • Overhead sign structures

27. Potential Hazards (continued) • Roadside Obstacles • Rock cuts • Longitudinal retaining walls • Ditches • Cliffs • Dropoffs • Bodies of Water • Projectiles: • Mailboxes • Fence Rails

28. Treatment Options: • Remove from clear zone • Relocate • Modify • Replace concrete headwall w/ flared end • Pour a smooth concrete wall against a rock cut • Place grates across drain pipe end sections • Replace posts w/ break-away posts • Shield • Guide railing • Impact attenuators • Delineate

29. Impact Attenuators • Used when fixed hazards can’t be removed or protected by railing (gore areas) • Inertial Systems-Transfers kinetic energy to series of yielding masses (sand barrels) http://www.crashcushions.com/rental.php http://epg.modot.org/index.php?title=Category:612_impact_attenuators

30. Impact Attenuators • Compression Systems-Absorbs energy by progressive deformation or crushing of the system elements (GREAT-Guardrail Energy Absorbing Terminal) http://www.acprod.com.au/images/product/ACP-NSW__SKT_product_brochure_1.jpg http://www.highwaysafety.net/endTreatments.htm

31. Guiderail is a Type 3 Box with a 'WYBET' terminal section.Picture taken in June 2011Location: Interstate 81 south in the town of Castle Creek, NY---from SUNYIT student who works for NYSDOT

32. Vaulting • When vehicle vaults over a barrier • Free to hit a FO • May roll over • Major Cause (Curbs) • Don’t use curbs w/ concrete barriers or cable • Minimize use of mountable curbs • Don’t use non-mountable curbing when operating speeds are >80 km/hr • Place curbs <1’ or more than 10’ from guide railing

33. Other • Fencing and cattle passes keep livestock and wild animals from entering the traveled way

34. Innovative Median Barriers: • Single Slope Concrete Median Barrier • Moveable Concrete Barrier • Truck Barrier • Cable Median Barrier