Single-Slope Concrete Bridge Rail

Transcription

1 TRANSPORTATON RESEARCH RECORD Sngle-Slope Concrete Brdge Ral KNG K. MAK, DON J. GRPNE, AND CHARLES F. MCDEVTT A sngle-slope concrete medan barrer was prevously desgned, developed, and successfully crash tested at the Texas Transportaton nsttute n accordance wth gudelnes set forth n NCHRP Report 230. The Washngton State Department of Transportaton s nterested n adaptng ths sngle-slope barrer desgn for use as a brdge ral. The re~ults of full-scale crash tests conducted on ths sngle-slope concrete bndge ral and the evaluaton of ts mpact performance are presented. The sngle-slope concrete brdge ral was judged to have successfully met all evaluaton crtera set forth n NCHRP Report 350 and the 1989 AASHTO Gude Specfcatons for Brdge Ralngs and s recommended for feld mplementaton. A sngle-slope concrete medan barrer was prevously desgned, developed, and successfully crash tested at the Texas Transportaton nsttute (TT) n accordance wth gudelnes set forth by Beason et al. (J) and n NCHRP Report 230 (2). The barrer was approved by FHW A and was adopted by many states for feld mplementaton. As mpled by ts name, ths sngle-slope barrer has a sngle sloped face at 79 degrees (or 11 degrees to the vertcal) and s 42 n. (1.07 m) hgh. The sngle-slope barrer has several advantages over the New Jersey safety-shaped barrer. Frst, the sngle-slope barrer has a lower propensty for causng rollover than the New Jersey safety-shaped barrer wthout greatly ncreasng the damage and lateral acceleraton to mpactng vehcles. Second, although the ntal constructon cost of the sngle-slope barrer s comparable to that of standard safety-shaped barrer, the mantenance costs and lfe cycle costs of the sngle-slope barrer should be substantally lower than those of the standard safetyshaped barrer. To mantan the shape and heght of the barrer for the standard safety-shaped barrer, the pavement surface must frst be lowered before any overlay can be appled to provde a new wearng surface. Ths s an expensve outlay over the lfe of the pavement and the barrer. On the other hand, a sngle-slope barrer can accommodate overlays wthout any concern for the shape of the barrer. Also, wth an ntal heght of 42 n. ( 1.07 m), the barrer can accommodate up to 10 n. (254 mm) of overlay, e.g., fve overlays of 2 n. (51 mm) each over the years, and stll has a heght of 32 n. (0.81 m), whch s the heght of the standard safety-shaped barrer. Thrd, the sngle-slope barrer can be advantageous n stuatons n whch there are dfferences n elevaton between the two sdes of dvded hghways, such as at superelevated curves. Because there s only a sngle sloped face, the heght of the barrer can be dfferent on the two faces to accommodate the dfference n elevaton wthout concern over the shape of the barrer. Ths can smplfy the constructon of the barrer, especally when slp-formng s used. The Washngton State Department of Transportaton (W adot) s nterested n adaptng ths sngle-slope barrer desgn for use as a brdge ral. Although the sngle-slope barrer desgn was orgnally K. K. Mak, Texas Transportaton nsttute, The Texas A&M Unversty, College Staton, Tex D. J. Grpne, Washngton Department of Transportaton, Olympa, Wash C. F. McDevtt, FHWA, Turner-Farbank Hghway Research Center, McLean, Va ntended for use as a medan barrer, there s no reason why t could not be used as a brdge ral. The key dfference between the medan barrer and the brdge ral applcatons would be the heght of the barrer, whch s 42 n. (1.07 m) for the medan barrer and 32 n. (0.81 m) for the brdge ral. On the bass of results of prevous crash tests, the mpact performance of the barrer should not be adversely affected when the barrer heght s lowered from 42 to 32 n. ( 1.07 to 0.81 m). The other dfference s that the brdge ral s ted nto the brdge deck, whereas the medan barrer s keyed n place wth an asphalt overlay. However, because the barrer remans essentally rgd n both applcatons, there should not be any effect on ts mpact performance. t should be noted that although the brdge ral was tested at. a ral heght of 32 n. (0.81 m), the brdge ral would perform satsfactorly at greater ral heghts. Presented n ths paper are the results of full-scale crash tests conducted on ths sngle-slope concrete brdge ral and the evaluaton of ts mpact performance. TEST NSTALLATON A schematc of the test nstallaton s shown n Fgure 1. Precast sngle-slope medan barrer sectons, prevously fabrcated by TT n another study, were used for the test nstallaton. The use of the precast sngle-slope medan barrer sectons saved the expenses of buldng a smulated brdge deck and the brdge ral. The ratonale for ths approach was that as long as the barrer remaned rgd t really would not matter whether the brdge ral was ted nto a smulated brdge deck. The concern was more wth the shape and geometrcs of the sngle-slope brdge ral and not the strength of the ral or ts te-n to the brdge deck. A schematc showng the rebar and connecton detals planned for use wth the sngle-slope brdge ral by WaDOT and approved by FHW A s shown n Fgure 2. Note that the connecton detals are adopted from the standard safety-shaped concrete brdge ral, whch has been successfully crash tested n prevous studes and was therefore not evaluated n the present study. Four 30-ft (9.14-m) precast barrer sectons were used for a total nstallaton length of 120 ft (36.6 m). The barrer sectons were connected wth channel connectors at the bottom, and rebar grds were placed n the grd slots and were grouted n place. A dtch 10 n. (254 mm) deep was dug for placement of the barrer sectons so that the heght of the barrer above ground level was reduced from 42 to 32 n, ( 1.07 to 0.81 m). The bottom of the dtch was lned wth base materals to ensure that the foundaton for the barrer was level and smooth. To ensure that the barrer sectons would reman rgd durng the mpacts, the barrer secton wthn whch the mpacts would occur was doweled nto the exstng concrete pavement wth No. 5 rebars spaced at 3 ft (0.91 m) center to center. Also, after the barrer was nstalled n the dtch, the back of the barrer was keyed wth a concrete overlay, 24 n. (0.61 m) wde and 4 n. (102 mm) thck, and the area between the exstng concrete pavement and the front of the barrer was backflled wth grout to make sure that the barrer

2 26 TRANSPORTATON RESEARCH RECORD 1468 l 3T Grouted Rebar Grd Connecton Epoxy Seated Dowel would reman rgd on mpact. Photographs of the test nstallaton are shown n Fgure 3. W adot plans to use a brdge ral heght of 34 n. (0.86 m), whch allows for a future overlay of 2 n. (51 mm). However, the crash tests were conducted wth a brdge ral heght of 32 n. (0.81 m) snce the lower ral heght was consdered a more crtcal test condton. The schematc n Fgure 2 showng the rebar and connecton detals s for a ral heght of 32 n. (0.81 m), whch was the ral heght evaluated n the crash tests. However, the detals for a 34-n. (0.86-m) sngle-slope brdge ral should be very smlar. Concrete wth Wre Mesh CRASH TEST MATRX FGURE 1 Sngle-slope concrete brdge ral test nstallaton. n accordance wth requrements set forth n the 1989 AASHTO Gude Specfcatons for Brdge Ralngs (3) (herenafter referred to "6 Spacng at 7" TYP--. X) N j! ~ '/z" -- / --- s at a" / ~ s Spacng at ~ l'-2" TYP 6'/a" 9Y2",... r1 "4 Contnuous wth ' ;...,...:/~ 1 2' -o" MN splce TYP 1 1 /z" Clearance TYP ~ Q) U g_ ~, c;1 :::J CT: W "'\! ' ' at 1 6" 1. 5 : :~nt;nuous w;th 2'-0" MN splce space at 7" MAX TYP FGURE 2 Renforcement and connecton detals planned for sngle-slope concrete brdge ral.

3 Mak et al. 27 test at 60 mph (96.6 km/hr) and 20 degrees, t should also perform smlarly to the 4,500-lb (2,043-kg) passenger car test at 60 mph (96.6 km/hr) and 25 degrees. However, although the large car successfully met the gudelnes set forth n NCHRP Report 230 (2), the vehcle exhbted a tendency to clmb up on the barrer. There was therefore concern that vehcle stablty mght become a problem wth the pckup truck when the barrer heght was reduced from 42 to 32 n. ( 1.07 to 0.81 m). Thus, the crash test wth the pckup truck was ncluded. t was also decded that the test condtons for the pckup truck test would be n accordance wth Test Level 4 of the new NCHRP Report 350 (4) requrements [.e., a 2,000-kg (4,409-lb) pckup truck strkng the brdge ral at a nomnal speed and angle of 100 km/hr (62.2 mph) and 25 degrees]. n summary, the actual crash test matrx used to evaluate the mpact performance of ths sngle-slope concrete brdge ral desgn ncluded only the pckup truck and the sngle-unt-truck crash tests. Testng and evaluaton were performed n accordance wth gudelnes outlned n NCHRP Report 350 (4) and the 1989 AASHTO Gude Specfcatons (3). FGURE 3 Sngle-slope concrete brdge ral test nstallaton. as the Gude Specfcatons) for a Performance Level 2 brdge ral, the followng three crash tests are requred: 1. An 1,800-lb (817-kg) passenger car strkng the brdge ral at a nomnal speed and angle of 60 mph (96.6 km/hr) and 20 degrees, 2. A 5,400-lb (2,449-kg) pckup truck strkng the brdge ral at a nomnal speed and angle of 60 mph (96.6 km/hr) and 20 degrees, and 3. An 18,000-lb (8,170-kg) sngle-unt truck strkng the brdge ral at 50 mph (80.5 km/hr) and 15 degrees. The crash test matrx was modfed for the testng of the sngleslope concrete brdge ralng. The 1,800-lb (817-kg) passenger car severty test was consdered unnecessary and was deleted from the crash test matrx. As mentoned prevously, the sngle-slope concrete medan barrer successfully passed the large car structural adequacy test and the small car severty test n accordance wth gudelnes set forth n NCHRP Report 230 (2). On the bass of the results of those crash tests, t was beleved that the barrer heght would have lttle or no effect on the small car severty test and there was therefore no need to repeat the test. As for the 5,400-lb (2,449-kg) pckup truck structural adequacy FGURE 4 Vehcle after Test

4 ;. : : : 'r. D : : : : : : ~ ~,- ~ ~ : :' : :' :~~,.. fd.. -~... -~... -~-... -~... -~... -~-... -~-... -~-... -~ ~28.2m General nformaton Test Agency.... Test No Date.... Test Artcle Type.... nstallaton Length (m) Sze and/or dmenson and materal of key elements.... Sol Type and Condton.. Test Vehcle Type.... Desgnaton.... Model.... Mass (kg) Curb Test nertal Dummy Gross Statc. Texas Transportaton nsttute /03/93 Brdge Ral Sngle Slope Concr ete 36.6 (120 ft) 81 cm (32 n) hgh concrete Producton Model 2000 p 1985 Chevrolet Custom 1,993 (4,390 lb) 2,000 (4,405 lbl 76 (167 lb) 2,076 (4,573 lb) mpact Condtons Speed (km/h).... Angle (deg).... Ext Condtons Speed (km/h).... Angle (deg).... Occupant Rsk Values mpact Velocty (m/s) x-drecton.... y-drecton THV (optonal).... Rdedown Acceleratons (g's) x-drecton.... y-drecton PHO (optonal).... AS (optonal).... Max sec Averages (g'sl x-drecton y-drecton z-drecton 97.2 (60.4 m/h (47.6 m/h) (17.7 ft/s) 7.8 (25.6 ft/s) Test Artcle Deflectons (cm) Dynamc.... Permanent.... Vehcle Damage Exteror VOS.... CDC.... nteror OCD Maxmum Exteror Vehcle Crush (cm) Max. Occ. Compart. Deformaton (cm) Post-mpact Behavor Max. Roll Angle (deg) Max. Ptch Angle (deg) Max. Yaw Angle (deg) 0.6 (0.3 n) 01RD5 01 FREK2 & 01RDEW2 RF (16.1 n) 13.9 (5.5 n) FGURE 5 Results for Test

5 Mak et al. 29 RESULTS OF CRASH TESTS Pckup Truck Crash Test (Test ) A 1985 Chevrolet C-20 Custom Deluxe pckup truck was used for the crash test. The test nerta weght of the vehcle was 2,000 kg (4,409 lb) and ts gross statc weght was 2,076 kg (4,577 lb), ncludng an unnstrumented 50th percentle male anthropometrc dummy restraned n the drver's seat wth lap and shoulder belts. The vehcle struck the brdge ral 12.2 m (40.0 ft) from the upstream end at a speed of 97.2 km/hr (60.4 mph) and an angle of 25.5 degrees. The rght front tre of the vehcle began to clmb the face of the barrer on mpact. Shortly thereafter the left front tre became arborne as the vehcle began to redrect. The rear of the vehcle then contacted the barrer, and shortly thereafter the rear wheels became arborne. The vehcle exted the harrer arborne, travelng at a speed of 76.5 km/hr (47.6 mph) and an angle of 3.3 degrees. The rght front tre came back nto contact wth the pavement, and the tre and rm separated from the wheel hub subsequent to the mpact wth the pavement. The rght rear tre and rm also separated from the wheel hub when the tre came back nto contact wth the pavement. The vehcle came to rest 77.4 m (254.0 ft) downstream and 21.2 m (69.5 ft) to the traffc sde of the pont of mpact. The barrer receved only cosmetc damage (.e., scrapes and tre marks), and there were two small cracks on the barrer. The vehcle was n contact wth the barrer for 4.2 m (13.9 ft). The entre vehcle sustaned extensve damage, as shown n Fgure 4. Maxmum deformaton nto the occupant compartment was 139 mm (5.5 n.) at the frewall area, and maxmum exteror crush at the rght front corner at bumper heght of the vehcle was 410 mm (16.1 n). The rght front wheel was pushed rearward 120 mm (4.7 n.), and the frame was bent. The occupant rsk factors were well wthn the preferred lmts set forth n NCHRP Report 350 (4) and the Gude Specfcatons (3). n the longtudnal drecton, occupant mpact velocty was 5.4 m/sec ( ft/sec), and the hghest sec average rdedown acceleraton was -6.1 g. Lateral occupant mpact velocty was 7.8 m/sec (25.6 ft/sec), and the hghest sec occupant rdedown acceleraton was g. A summary of the test results s provded n Fgure 5. (8.5 ft) to the left of the pont of mpact (.e., to the traffc sde of the brdge ral). The barrer receved only cosmetc damage (.e., gouges, scrapes, and tre marks). The vehcle was n contact wth the barrer for 15.6 m (51.2 ft). The vehcle sustaned extensve damage to the front suspenson, as shown n Fgure 6. Maxmum crush at the rght front corner of the vehcle was 178 mm (7.0 n.). The front axle was separated from the vehcle, and the sprng shackles, U-bolts, shocks, mounts, te rods, and steerng arm were damaged. n addton, damage was sustaned by the front bumper, the rght front quarter-panel, and the rght and left runnng boards. The wndsheld was cracked, and the fuel tank was scraped. The occupant rsk factors were well wthn the lmts set forth n the Gude Specfcatons (3). n the longtudnal drecton, occupant mpact velocty was 2.3 m/sec (7.5 ft/sec), and the hghest sec average rdedown acceleraton was -1.3 g. Lateral occupant mpact velocty was 3.5 m/sec (11.5 ft/sec), and the hghest sec occupant rdedown acceleraton was -2.6 g. A summary of the test results s gven n Fgure 7. Sngle-Unt-Truck Crash Tests (Tests and ) A 1982 GMC sngle-unt truck wth an empty weght of 5,262 kg (11,590 lb) was used for the second crash test (Test ). The vehcle was ballasted wth sandbags to a test nerta and gross statc weght of 8, 172 kg ( 18,000 lb). The vehce struck the brdge ral 13.7 m (45.0 ft) from the upstream end at a speed of 82.1 km/hr (51.0 mph) and at an angle of 10 degrees. Shortly after mpact wth the brdge ral the front axle separated from the vehcle. The rght lower corner and edge of the box van then set down on top of the ral and rode along n ths fashon untl the vehcle rode off the end of the brdge ral test nstallaton. The box van reached a maxmum roll angle of 23 degrees, and the cab reached a maxmum roll angle of 25 degrees. The box van then began to rght tself and came to rest uprght 65.4 m (214.5 ft) downstream and 2.6 m FGURE 6 Vehcle after Test

6 --~~~-L-~-= =-:es_.m_-_-_-_-_-_-_-_-_- :-.~~ ~-:---.~ej: CU<t Ut W U rt General nformaton Test Agency.... Test No.... Date.... Test Artcle Type.... nstallaton Length (m) Sze and/or dmenson and materal of key elements.... Sol Type and Condton Test Vehcle Type.... Desgnaton.... Model.... Mass (kg) Curb.... Test nertal. Dummy... Gross Statc. Texas Transportaton nsttute /06/93 Brdge Ral Sngle Slope Concrete 36.6 (120 ft) 81 cm (32 n) hgh concrete Producton Model 8000 s 1982 GMC Sngle-Unt Truck 5,262 (11,590 lb) 8, 172 (18,000 lb) NA 8,172 (18,000!b) mpact Condtons Speed (km/h).... Angle (deg).... Ext Condtons Speed (km/h).... Angle (deg).... Occupant Rsk Values mpact Velocty (ms) x-drecton y-drecton.... THV (optonal).... Rdedown Acceleratons (g's) x-drecton.... y-drecton.... PHO (optonal).... AS (optonal).... Max sec Averages (g's) x-drecton.... y-drecton z-drecton 82.1 (51.0 m/h) 10.0 NA (7.5ft/s) 3.5 (11.5 ft/s) Test Artcle Deflectons (cm) Dynamc.... Permanent.... Vehcle Damage Exteror VOS.... CDC nteror OCD Maxmum Exteror Vehcle Crush (cm).. Max. Occ. Compart. Deformaton (cm) Post-mpact Behavor Max. Roll Angle (deg) Max. Ptch Angle (deg) Max. Yaw Angle (deg). NA 0.2 (0.1 n) RFOOOOOOO 17.8 (7.0 n) FGURE 7 Results for Test

7 Mak et al. 31 The vehcle struck the brdge ral at an angle of 10 degrees nstead of the requred 15 degrees. An extensve nvestgaton revealed that the gudance cable release mechansm dd not functon properly, causng the front tres to tum to the left abruptly, whch n tum caused the truck to yaw counterclockwse. Because of the lower-than-requred mpact angle n the frst sngle-unt-truck test, the sngle-unt-truck test was repeated (Test ). A 1985 GMC sngle-unt truck was used for ths test. The vehcle struck the brdge ral 13.1 m ( 43.0 ft) from the upstream end at a speed of 82.5 km/hr (51.3 mph) and an angle of 17.9 degrees. Shortly after mpact, the rght front tre began to clmb the face of the brdge ral and the front axle became partally separated from the vehcle. The box van began to roll to the rght, reachng a maxmum roll angle of 53 degrees. The lower rght comer and edge of the box van set down on top of the brdge ral and rode along n ths fashon untl the vehcle rode off the end of the brdge ral test nstallaton. After the vehcle rode off the end of the brdge ral test nstallaton, the front axle separated from the vehcle as the front end contacted the pavement and the rear tres of the vehcle dug nto the drt. The vehcle began to roll to the left and eventually rolled onto ts left sde. The vehcle came to rest 49.7 m (163.0 ft) downstream and 2.9 m (9.5 ft) behnd the pont of mpact. The barrer agan receved only cosmetc damage (.e., gouges, scrapes, and tre marks). The vehcle was n contact wth the barrer for 23.5 m (77.0 ft). The vehcle sustaned extensve damage, as shown n Fgure 8. Maxmum crush at the rght front comer of the vehcle was 22.9 cm (9.0 n.). The front axle was separated from the vehcle, and the front suspenson was damaged extensvely. n addton, damage was sustaned by the front bumper and grll and the rght front fender, door, and runnng board. The entre left sde of the vehcle sustaned dents and scrapes due to rollover on the left sde. The fuel tanks were scraped on both sdes. The occupant rsk factors were agan well wthn the lmts set forth n the Gude Specfcatons (3). n the longtudnal drecton, occupant mpact velocty was 2.9 m/sec (9.7 ft/sec), and the hghest sec average rdedown acceleraton was -2.7 g. Lateral occupant mpact velocty was 2.8 m/sec (9.3 ft/sec), and the hghest sec occupant rdedown acceleraton was-10.2 g. A summary of the test results s gven n Fgure 9. The mpact angle of 17.9 degrees was greater than the requred angle of 15 degrees. Extensve nvestgaton, ncludng detaled analyss of photographc and electronc data, faled to reveal any potental problems that could have caused ths hgher-than-requred mpact angle. SUMMARY OF FNDNGS FGURE 8 Vehcle after Test The sngle-slope concrete brdge ral was judged to have successfully met all evaluaton crtera set forth n NCHRP Report 350 (4) and the 1989 AASHTO Gude Specfcatons (3) and s recommended for feld applcatons. For the pckup truck test (Test ), the sngle-slope concrete brdge ral contaned and smoothly redrected the vehcle. There were no detached elements or debrs to cause undue hazard to the occupants of the vehcle or to adjacent traffc. The vehcle sustaned moderate damage wth mnor deformaton nto the occupant compartment. The vehcle remaned uprght and relatvely stable durng the collson perod; however, there were some moderate ptchng and yawng after the vehcle exted from the brdge ral. Although the vehcle came to rest 21.2 m (67.5 ft) from the traffc sde of the brdge ral, the trajectory of the vehcle was judged to pose mnmal potental hazard to adjacent traffc. Part of the vehcle trajectory could be attrbuted to the separaton of the tres and rms from the wheel hubs for the two rght-sde tres. Also, the ext angle of 3.3 degrees was substantally less than 60 percent of the mpact angle. The occupant mpact veloctes and rdedown acceleratons were well wthn the lmts set forth n NCHRP Report 350 (4) and the 1989 AASHTO Gude Specfcatons (3). For the two sngle-unt-truck tests (Tests and ), the sngle-slope concrete brdge ral contaned and redrected the test vehcles and dd not allow the vehcles to penetrate or go over the brdge ral. There were no detached elements or debrs from the brdge ral to present undue hazard to occupants n the vehcles or other adjacent traffc. The ntegrty of the occupant compartment was mantaned. n Test the vehcle remaned uprght and relatvely stable durng and after the collson. n Test the vehcle remaned uprght durng collson wth the brdge ral, but then rolled over onto ts left sde (nonmpact sde) after extng from the brdge ral test nstallaton. The rollover occurred on the traffc sde of the brdge ral, whch s consdered acceptable under the evaluaton crtera set forth n the 1989 AASHTO Gude Specfca-

8 ,-r\ "j. ' - ",...,... : ~~~.. '@:'... General nformaton Test Agency.... Test No Date.... Test Artcle Type.... nstallaton Length (ml Sze and/or dmenson and materal of key elements.... Sol Type and Condton.. Test Vehcle Type.... Desgnaton.... Model.... Mass (kgl Curb Test nertal Dummy Gross Statc. Texas Transportaton nsttute /06/93 Brdge Ral Sngle Slope Concrete 36.6 (120 ftl 81 cm (32 nl hgh concrete Producton Model 8000 s 1985 GMC Sngle-Unt Truck 5,207 (11,470 lbl 8, 172 (18,000 lb) 8, 172 (18,000 lb) mpact Condtons Speed (km/h).... Angle (deg).... Ext Condtons Speed (km/h).... Angle (deg).... Occupant Rsk Values mpact Velocty (m/s) x-drecton.... y-drecton.... THV (optonal).... Rdedown Acceleratons (g's) x-drecton.... y-drecton.... PHO (optonal).... AS (optonal).... Max sec Averages (g's) x-drecton.... y-drecton.... z-drecton Test Artcle Deflectons 82.5 (51.3 m/h) (cml 17.9 Dynamc... Permanent (0.1 n) 0 Vehcle Damage Exteror VOS (9.7 ft/s) CDC (9.3 ft/s) nteror OCD... RFOOOOOOO -2.7 Maxmum Exteror Vehcle Crush (cm) Max. Occ. Compart. Deformaton (cm) -2.0 Post-mpact Behavor -5.6 Max. Roll Angle (deg) Max. Ptch Angle (deg) 4.3 Max. Yaw Angle (deg) FGURE 9 Results for Test

9 Mak et al. 33 tons (3). The vehcle trajectory dd not pose any potental hazard to adjacent traffc n ether test. The mpact angles for the two sngle-unt-truck tests were too low (10 degrees) n the frst test and too hgh (17.9 degrees) n the second test. However, because both tests successfully met all evaluaton crtera, t s reasonable to argue that the sngle-slope concrete brdge ral would have performed satsfactorly had the mpact angle been at the requred 15 degrees. A revew of the two tests showed that, for the test wth the hgher mpact angle, the vehcle was less stable wth a much hgher roll angle toward the barrer and a slghtly hgher clmb on the barrer durng mpact wth the brdge ral. Of course, the vehcle rolled over after extng from the brdge ral n the test wth the hgher mpact angle. REFERENCES 1. Beason, W. L., H. E. Ross, Jr., H. S. Perera, and W. L. Campse. Development of a Sngle Slope Concrete Medan Barrer. Fnal Report 9429C-1. Texas State Department of Hghways and Publc Transportaton, Austn, Feb Mche, J. D. NCHRP Report 230: Recommended Procedures for the Safety Performance Evaluaton of Hghway Appurtenances. TRB, Natonal Research Councl, Washngton, D.C., March Gude Specfcatons for Brdge Ralngs. AASHTO, Washngton, D.C., Ross, H. E., Jr., D. L. Sckng, R. A. Zmmer, and J. D. Mche. NCHRP Report 350: Recommended Procedures for the Safety Performance Evaluaton of Hghway Features. TRB, Natonal Research Councl, Washngton, D.C., 1993.