Appurtenances HDM Ch 10 1 Kinetic Energy gforces

Appurtenances HDM Ch. 10 1

Kinetic Energy (g-forces) n A car weighs 3000 pounds At 20 mph KE=40, 000 ft-lb (0. 5 mv 2) n At 40 mph KE=160, 000 ft-lb n If the car above stops in 50 ft Average deceleration in g’s is 1. 07 for a car starting at 40 mph n n 2

Equations n Kinetic Energy = 0. 5*Mass*V 2 n Avg Deceleration (in g’s) for a car at some initial speed decelerating to a stopping condition over some length L: n V 2/(2*g*L) 3

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

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 5

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

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

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

9

Non-Recoverable 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 10

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 11

12

Clear Runout Width (CRW) Width provided at the toe of a traversable, nonrecoverable fill slope Minimum width should be 2. 5 m (why that #? ) 13

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

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

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

17

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

19

Barrier Types n n Cable Guide Rail Corrugated Metal (W-beam) (1. 5*cable) Box Beam (3*cable) Concrete (10*cable) 20

21

22

23

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

Selecting Guide Rail n n n 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 q n (tree dia. > 100 mm is considered a hazard) Deflections must stay within ROW 25

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

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

Treatment Options: Remove from clear zone Relocate Modify 1. 2. 3. q q Shield 4. q q 5. 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 Guide railing Impact attenuators Delineate 28

Impact Attenuators n n 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 29

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

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

Vaulting n When vehicle vaults over a barrier q q n Free to hit a FO May roll over Major Cause (Curbs) q q 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

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

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