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: Fixed Objects: 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 Shield
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)

30. Impact Attenuators
Compression Systems-Absorbs energy by progressive deformation or crushing of the system elements (GREAT-Guardrail Energy Absorbing Terminal)

31. Guiderail is a Type 3 Box with a 'WYBET' terminal section
Guiderail is a Type 3 Box with a 'WYBET' terminal section. Picture taken in June 2011 Location: 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 Major Cause (Curbs)
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