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1 Appurtenances HDM Ch. 10. 2 Kinetic Energy (g-forces) A car weighs 3000 pounds At 20 mph KE=40,000 ft-lb (0.5mv 2 ) At 40 mph KE=160,000 ft-lb If the.

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Presentation on theme: "1 Appurtenances HDM Ch. 10. 2 Kinetic Energy (g-forces) A car weighs 3000 pounds At 20 mph KE=40,000 ft-lb (0.5mv 2 ) At 40 mph KE=160,000 ft-lb If the."— Presentation transcript:

1 1 Appurtenances HDM Ch. 10

2 2 Kinetic Energy (g-forces) A car weighs 3000 pounds At 20 mph KE=40,000 ft-lb (0.5mv 2 ) 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*V 2 Avg Deceleration (in g’s) for a car at some initial speed decelerating to a stopping condition over some length L: V 2 /(2*g*L) 3

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

5 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 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 7 Clear Zone Based on: Design Speed Traffic Volume Roadside Slope Curvature of the Road

8 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

9 9

10 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 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

12 12

13 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 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 15 Design Clear Zone Width Should be at least the minimum and preferably greater than the minimum

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

17 17

18 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

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

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

25 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 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 27 Potential Hazards (continued) Roadside Obstacles  Rock cuts  Longitudinal retaining walls  Ditches  Cliffs  Dropoffs  Bodies of Water Projectiles:  Mailboxes  Fence Rails

28 28 Treatment Options: 1. Remove from clear zone 2. Relocate 3. 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 4. Shield  Guide railing  Impact attenuators 5. 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) 29 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) 30 http://www.acprod.com.au/images/product/AC P-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 2011 Location: Interstate 81 south in the town of Castle Creek, NY--- from SUNYIT student who works for NYSDOT 31

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 32

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

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


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