Semirigid barriers include strong-post, corrugated beam (e.g.W-beam, thrie beam) guardrail systems. Although variations of thesesystems have been successfully tested near steep slopes (1), their instal-lation can be difficult because of deep embedment depths of the postsor smaller post spacing that are characteristic of these designs. Further,the maintenance and repair of impact damage required for these semi-rigid systems can pose additional risk to workers because of the closeproximity of both traffic and the hazardous slope condition.

Use of a more rigid concrete barrier system can mitigate the costand risk of maintenance and repair. They are often selected wherespace is constrained and only a small amount of deflection is allow-able. These systems are also used where there is a frequent occurrenceof impacts and a reduced maintenance is desired.

Concrete barriers can be cast in place or installed in precast sec-tions. Cast-in-place construction can require more time on-site to buildforms, pour the concrete, and allow for curing. This time results in anincrease in disruption to traffic and more exposure for constructionworkers. Concrete barriers are typically designed with the barrierembedded in the ground, keyed in the pavement, or with some type offoundation to make it rigid. This configuration is relatively typical formedian applications. However, no testing has been performed forthese keyed or embedded barriers in a configuration where the barrieris installed on the roadside adjacent to a steep slope. Some of the con-crete barriers designs have used vertical steel pins that pass throughholes in the barrier and continue some distance into the ground torestrict lateral barrier movement. The barriers in these designs weretested while placed on asphalt or concrete pavements, which helpedreduce deflections during vehicle impacts. Such designs, however, aretypically used in temporary barrier applications.

In the absence of a restraining mechanism, designers recommendseveral feet of embankment behind a concrete barrier to develop therequired strength and barrier stability during an impact. When thisspace is not available, current design practice requires the use of abelow grade moment slab similar to the one depicted in Figure 1.However, the installation of a cast-in-place moment slab (whichincludes excavation, forming, concrete placement, and compactionof soil backfill) can be expensive and requires an additional con-struction phase to build the slab. Because the slab is normally underthe shoulder and possibly the lanes, the disruption of traffic flow isincreased. A cost-effective barrier system that has limited deflectionand low maintenance and repair needs is needed for use on adjacentto steep slopes.

OBJECTIVE

The objective of the research presented here was to develop a cost-effective, concrete barrier system that can be placed in front ofslopes as steep as 1.5H:1V. The design constraints excluded use of

Application of Precast Concrete BarrierAdjacent to Steep Roadside Slope

Nauman M. Sheikh, Roger P. Bligh, Richard B. Albin, and Dave Olson

121

When concrete barriers are installed adjacent to drop-offs or steep road-side slopes such as 1.5H:1V, a cast-in-place concrete moment slab is usu-ally attached to the base of the barrier to resist lateral and overturningforces during vehicle impact. Cast-in-place construction can requiremore time on-site to build forms, pour the concrete, and allow for cur-ing. This time constraint results in an increase in disruption to traffic andmore exposure for construction workers. Furthermore, the installationof a moment slab is very costly and requires an additional constructionphase to build the slab. Because the slab is normally under the shoulderand possibly the lanes, the disruption of traffic flow is increased. A newapplication of a precast 42-in.-tall single-slope concrete barrier for use infront of steep slopes was developed that does not require a moment slab.The lateral movement of the barrier is restricted by embedding it in soil.This design also reduces the embankment behind the barrier to 2 ft. Theembedded barrier application was successfully evaluated under Manualfor Assessing Safety Hardware Test Level 3 criteria. The permanentdeflection of the barrier was 5.5 in. The use of the embedded concretebarrier in lieu of the typically installed barrier with a moment slab isexpected to result in cost savings of approximately $300 per linear footand reduced time to construct.

Roadside barriers are used to shield motorists from hazards locatedoff the traveled way. A naturally occurring hazard common in moun-tainous regions and constrained environments is a steep, nontravers-able roadside slope. Available right-of-way along highways in theseregions is often restricted. Thus, it is desirable to place the barrier asclose to the slope break point as possible to maximize available spacefor travel lanes and shoulders.

Various types of roadside barriers have met current crash test cri-teria and been accepted for use on the National Highway System.These barriers are generally categorized as flexible, semirigid, orrigid depending on their deflection characteristics. Although flexi-ble systems typically have lower injury probability because of theirmore forgiving nature, their use is often limited as a result of thespace required to accommodate their high design deflections. Thus,when installing a barrier near to a steep, nontraversable slope, asemirigid or rigid system is often preferred.

N. M. Sheikh and R. P. Bligh, Texas Transportation Institute, Texas A&M UniversitySystem, MS-3135, College Station, TX 77843-3135. R. B. Albin, Federal HighwayAdministration, 12300 West Dakota Avenue, Suite 340, Lakewood, CO 80228. D. Olson, Washington State Department of Transportation, P.O. Box 47329,Olympia, WA 98504-7329. Corresponding author: N. M. Sheikh, nauman@tamu.edu.

Transportation Research Record: Journal of the Transportation Research Board,No. 2195, Transportation Research Board of the National Academies, Washington,D.C., 2010, pp. 121–129.DOI: 10.3141/2195-13

a moment slab and permitted no more than 2 ft of offset from theslope break point. The barrier system was required to meet theimpact performance criteria recommended in the AASHTO Manualfor Assessing Safety Hardware (MASH) (2) and have a deflection ofless than 12 in. for a design impact. If embedment of the barrier wasrequired, the depth of embedment was limited to 10 in.

DESIGN AND ANALYSIS

The design and analysis was performed using the single or constantslope barrier profile. This profile was used because of the ease ofembedment if needed. A standard single slope barrier is 42 in. talland can be embedded 10 in. without needing a change in its profile.At a 10-in. embedment, the barrier would still have a height of 32 in.above the ground, which is typical of most other concrete barrierssuch as the New Jersey and F-shape barriers. The barrier used in thisresearch was precast with a 20-ft segment length. Adjacent barriersegments were connected using the grouted rebar–grid connection.This connection type and segment length is typically used by theparticipating pooled fund states.

Evaluation of Free-Standing Barrier

In 1989, the Texas Transportation Institute performed crash testingof the single-slope barrier with the grouted rebar–grid connection,but the barrier was keyed into an asphalt layer, which prevented itslateral movement. Another test was performed under the sameproject with the free-standing single slope barrier, but the rebargrid connection was not grouted (3). To date, no testing has beenperformed with the single slope barrier using the grouted rebar–gridslot connection in a free-standing condition. As a first step, theresearchers evaluated the performance of the free-standing singleslope barrier. The objective of this evaluation was to determinewhether this connection provided sufficient strength to transfermoments between adjacent barrier segments and cause them todeflect as a single body during vehicle impact, without significantrotation at the joints. If this could be achieved, it was believed thatthe impacting vehicle can be contained and redirected withoutsignificant barrier deflection simply using the weight of the con-crete barrier. This would have also rendered the easiest solutionto the design problem and allowed maximum flexibility in the useof the barrier.

122 Transportation Research Record 2195

To evaluate the performance of the free-standing single slope bar-rier with grouted rebar–grid connection, the researchers first deter-mined the response of a single barrier connection using surrogatebogie vehicle testing. Two 42-in. tall and 20-ft long single-slope bar-rier segments were connected using the grouted rebar–grid connec-tion. The outside ends of the barrier segments were constrained frommoving laterally by a 5-in. diameter pipe that was anchored to the con-crete pavement, as shown in Figure 2a. A 5,000-lb bogie vehicleimpacted the barrier at the connection with an impact speed of 14 mphand an angle of 90°. The impact in the test resulted in a maximum per-manent lateral deflection of 22 in. Because of the impact, the groutedrebar–grid connection cracked near the centerline of the connection.

The researchers used finite element modeling analysis to evalu-ate the barrier performance during different stages of this research.The general modeling and simulation approach are presented in thispaper. Greater specifics about finite element modeling and analysiscan be found elsewhere (4).

A finite element model of the barrier installation used in the bogietest was developed. A surrogate grouted rebar–grid connectionwas modeled with a block of bilinear elastic–plastic material and arebar–grid consisting of beam elements. Simulations were performedwith a 5,000-lb bogie vehicle impacting the barrier connection at testspeed and location. The properties of the surrogate connection in thesimulation were calibrated to match the lateral deflection of the bar-rier observed in the test. Figure 2b shows the calibrated simulationresults compared with the crash test results.

Once the response of a single grouted rebar–grid connection wascalibrated, the researchers used it to develop a full-scale barrier sys-tem model of a 100-ft long installation of the free-standing singleslope barrier. It was then evaluated under MASH Test Level 3 (TL-3)impact conditions (i.e., impact with a 5,000-lb vehicle at 62 mph and25°). The objective of this simulation was to determine whether theoverall lateral deflection of the free-standing barrier installation wassmall enough to allow its use adjacent to steep slopes. The barrier sys-tem model consisted of five 20-ft long single-slope barrier segmentsconnected using the calibrated grouted rebar–grid connection model.A 5,000-lb vehicle impacted the barrier 4 ft upstream of the connec-tion between the second and the third barrier segment. Simulationresults indicated that the free-standing barrier will result in deflectionof more than 30 in. in a full-scale 5,000-lb vehicle impact at 62 mphand 25°. This deflection was much higher than acceptable per theobjectives of this research. Hence, the researchers started evaluatingthe performance of the barrier when restrained by embedding it in soil.

The vehicle model used in the simulation analysis was origi-nally developed by the National Crash Analysis Center with furthermodifications from Texas Transportation Institute researchers. This4,409-lb pickup truck model was developed and widely used as adesign vehicle model specified in NCHRP Report 350 criteria (5),which preceded the more recent MASH criteria. Whereas NCHRPReport 350 required a 4,409-lb, 3⁄4-ton, standard cab pickup truck,MASH requires a 5,000-lb, 1⁄2-ton, four-door pickup truck. A publicdomain finite element model of the 5,000-lb, 1⁄2-ton, four-doorpickup truck was not available during the period of this research.The researchers increased the mass of the available 4,409-lb pickuptruck model by distributing additional mass over different parts of thevehicle and bringing the total vehicle mass to 5,000-lb. Doing soenabled the researchers to impart the same level of impact energyinto the barrier system as required by MASH. Because of the differ-ences in vehicle types and vehicle inertia characteristics, it wasexpected that the vehicle dynamics response of the 5,000-lb vehiclemodel would not match the vehicle response observed in a crash

8"

32"

12"

10"

42"

24"

28.6"

4.5'

54"

FIGURE 1 Single-slope barrier with a moment slab.

Sheikh, Bligh, Albin, and Olson 123

(a)

(b)

FIGURE 2 Evaluation of free-standing rebar–grid connection using bogie testing and simulation analysis: (a) bogie test setup and (b) test andsimulation results.

test. However, previous testing of the single-slope barrier had shownthat the vehicle remains fairly stable during the impact (3). Thus thevehicle dynamic characteristics were not deemed as critical, andaccounting for the increased vehicle mass was expected to enable asuccessful evaluation of the barrier system for the MASH criteria.

Evaluation of Embedded Barrier

To evaluate the barrier in embedded configuration, the researchersconducted another bogie impact test with two single-slope barriersegments connected via grouted rebar–grid connection and embed-ded 10 in. in soil behind the barrier. The width of the soil was 24 in.behind the barrier and a 1.5H:1V slope was used for the soil cut, asshown in the test setup in Figure 3a. The type of soil and the com-paction method used were as specified in the MASH criteria. Use ofthis bogie test helped evaluate the response of a single grouted

124 Transportation Research Record 2195

rebar–grid connection when embedded in a 10-in. soil layer. As aresult of the impact from a 5,004-lb bogie vehicle at a speed of14.4 mph, the maximum permanent barrier deflection was 4.45 in.at the joint. The researchers then incorporated the 10-in. soil layerinto the finite element model of the bogie test and calibrated soilproperties to match the barrier deflection observed in the test (seeFigure 3b).

Once the response of a single grouted rebar–grid connection withsoil behind the barrier was calibrated, the researchers developed a full-scale system model to evaluate a 100-ft-long installation. The instal-lation model consisted of five 20-ft-long single-slope barrier segmentsconnected using grouted rebar–grid connection and embedded 10 in.in soil in front of and behind the barrier. The widening of the soilbehind the barriers was 2 ft, and the slope of the soil embankmentwas 1.5H:1V, as in the bogie test. A simulation was performed witha 5,000-lb vehicle impacting the barrier at 25° and 62 mph. Thevehicle impacted the barrier 4 ft upstream of the connection between

(a)

(b)

FIGURE 3 Evaluation of embedded barrier with grouted rebar–grid connection using bogie testing and simulation analysis: (a) bogie testsetup and (b) test and simulation results.

the second and the third barrier segment. The vehicle was success-fully contained and redirected by the embedded barrier system in astable manner (see Figure 4). The maximum permanent deflection ofthe barrier was 9.75 in., which was within the 12-in. limit specifiedin the design objectives.

On the basis of results of the simulation analysis, the researchersrecommended performing a crash test with the single-slope barrierby embedding it 10 in. in soil.

FULL-SCALE CRASH TEST

Test Article Design and Construction

The test article consisted of a 100-ft-long installation of single-slopeconcrete barrier embedded 10 in. in soil. Five 20-ft-long barrier seg-ments were connected using the grouted rebar–grid slot connectionto achieve the 100-ft installation length.

The single-slope barrier segments were 42 in. tall, 24 in. wide atthe base, and 8 in. wide at the top. At each end of the barrier seg-ments, a 3-in. wide, 24-in. deep, and 10.5-in. long slot was cast intothe barrier to incorporate the grouted rebar–grid connection. Theconcrete reinforcement of the barrier segments consisted of #4 ver-tical bars that were bent to approximately match the profile of thebarrier faces and were spaced 12 in. apart along the length of the bar-rier. The spacing of the vertical bars was reduced around the slot castat each end for the grouted rebar–grid connection. In addition to thevertical bars, ten #5 longitudinal bars were located along the heightof the barrier. The barrier segments had a 4-in. wide and a 2-in. highslot cast at the bottom.

The barrier was embedded in crushed limestone road base materialthat conformed to MASH standard soil. To embed the barrier, a2-ft depth of the native soil adjacent to the testing facility’s concretepavement was excavated. The excavated area was then backfilledwith standard MASH soil and compacted in approximately 6-in.lifts. Once the backfill soil reached a level of 10 in. below the con-crete pavement surface, the barrier was set in place and further soilwas added and compacted in front and back of the barrier. The bar-rier was placed adjacent to the concrete pavement at a 1-ft lateral

Sheikh, Bligh, Albin, and Olson 125

offset. The soil widening behind the barrier was 2 ft. As the soil wasbackfilled, a 1.5H:1V slope was built into the embankment.

A rebar–grid was then dropped into the slot at each barrier con-nection location. It consisted of two vertical #6 bars that werespaced 10 in. apart and three longitudinal #8 bars that were spaced8 in. apart. With the rebar–grid in place, the connection was groutedusing a nonshrink grout. Details of the test article and its installationare shown in Figure 5.

The concrete of the barrier was specified to have a minimum com-pressive strength of 4,000 psi. The reinforcing steel was specified tobe grade 60 steel. The steel material used for manufacturing therebar–grid was also specified to be grade 60. The grout used for mak-ing the connection was a nonshrink grout with a minimum strength of4,000 psi. The soil used for embedding the barriers was crushed lime-stone road base material that conforms to standard MASH soil. Themoisture content of the soil on the day of the test was 8.5%.

The process of embedding the barrier in the field may be differ-ent from the test. The barrier can be installed by first compacting thesoil to roadway surface and then excavating a 2-ft-wide area forembedding the barrier. Once the barrier has been placed, some levelof compaction may be needed, depending on site conditions. If com-paction is needed behind the barrier, a compactor placed on a swingarm can be used.

Testing Requirements

According to MASH, two tests are recommended to evaluate longitudinal barriers for TL-3 as described here:

MASH Test Designation 3-10. 2,425-lb vehicle impacting the crit-ical impact point of the length of need section at a speed of 62 mphand an angle of 25°.

MASH Test Designation 3-11. 5000-lb pickup truck impactingthe critical impact point of the length of need section at a speed of62 mph and an angle of 25°.

The researchers performed Test 3-11 of MASH (i.e. 5,000-lbvehicle, 62 mph, 25°) on the design finalized from the simulation

(a)

(b)

FIGURE 4 Simulation results with 100-ft installation of single-slope barrier embedded 10 in. in soil: (a) initial state and (b) final state.

126 Transportation Research Record 2195

END VIEW

ELEVATION

PLAN

FIGURE 5 Test article details and barrier installation.

effort to verify simulation results. It was argued that this is the crit-ical test for the design, and the test with smaller 2,425-lb vehicle isnot needed. Because of higher impact energy, the test with the5,000-lb pickup truck will result in greater lateral deflection and helpevaluate connection strength and the tendency of the barriers to rotate.An impact resulting from the lighter 2,425-lb passenger car undersame impact speed and angle will not result in any increase in lateraldeflection of the barrier, nor will it impart a higher force on the bar-rier to evaluate connection strength and barrier rotation. Furthermore,because of the small deflection expected in the test, the small carimpact with the embedded single-slope barrier will be no differentthan the rigid single-slope barrier. Thus, the test was conducted withthe 5,000-lb pickup only.

Test Description

MASH Test 3-11 involves a 2,270P vehicle weighing 5,000 lb ±100 lb and impacting the barrier at an impact speed of 62.2 mph ±2.5 mph and an angle of 25° ± 1.5°. A 2002 Dodge pickup truck wasused in the test, which weighed 4,953 lb. The vehicle impacted the bar-rier with a speed and angle of 63.1 mph and 24.2°, respectively. Thetest impact point was 62.0 in. upstream of the joint between Segments2 and 3. At approximately 0.042 s, the left front tire began to climb theface of the barrier, and the vehicle began to redirect. At 0.169 s, thevehicle began to travel parallel to the barrier while traveling at a speedof 58.7 mph. At 0.173 s, the right rear of the vehicle contacted thebarrier, and at 0.176 s, the vehicle began to roll clockwise. The rightrear corner of the bed of the vehicle contacted the top of the barrierat 0.616 s, and after that, dust obscured the view in all cameraviews. Brakes on the vehicle were applied at 1.5 s after impact, andthe vehicle came to rest 247 ft downstream of impact and 10 fttoward traffic lanes.

Damage to Test Installation

Damage to the impacted barrier segments was minimal, as shown inFigure 6a. Tire marks were on the traffic face of the barrier and therewas no evidence of cracking in the barrier. Length of contact of thevehicle with the barrier was 14.0 ft. Maximum permanent deflectionof the barrier was 5.5 in. The working width was 19.6 in. Maximumdynamic deflection during the test was 5.6 in.

Vehicle Damage

The 2270P vehicle sustained damage to the right front corner and alongthe right side, as shown in Figure 6b. The right upper A-arm, right tierod end, and sway bar were deformed. Also damaged were the frontbumper, grill, right-front fender, right-front and rear doors, right-exterior side of bed, rear bumper, and tailgate. The right-front and rearwheel rims were deformed and the right-front tire was deflated. Max-imum exterior crush to the vehicle was 14.0 in. in the side plane at theright-front corner at bumper height. Maximum occupant compartmentdeformation was 0.5 in. in the right-front door at hip height.

Occupant Risk Factors

Data from the accelerometer, located at the vehicle’s center of grav-ity, were digitized for evaluation of occupant risk and were com-puted as follows. In the longitudinal direction, the occupant impactvelocity was 12.1 ft/s (3.7 m/s) at 0.090 s, the highest 0.010-s occu-

Sheikh, Bligh, Albin, and Olson 127

pant ridedown acceleration was −2.4 Gs from 0.173 to 0.183 s, andthe maximum 0.050-s average acceleration was −6.5 Gs between0.009 and 0.059 s. In the lateral direction, the occupant impactvelocity was 24.6 ft/s (7.5 m/s) at 0.090 s, the highest 0.010-s occu-pant ridedown acceleration was −11.3 Gs from 0.187 to 0.197 s, andthe maximum 0.050-s average was −13.0 Gs between 0.026 and0.076 s. These data and other pertinent information from the test aresummarized in Figure 7.

Assessment of Test Results

An assessment of the crash test on the basis of the applicable MASH08 safety evaluation criteria is presented in Table 1. As shown, theembedded single-slope barrier with grouted rebar grid connection

(a)

(b)

FIGURE 6 Test article and vehicle damage (a) test article damageand (b) vehicle damage.

128 Transportation Research Record 2195

0.000 s 0.098 s 0.296 s 0.393 s

General InformationTest Agency.............................Texas Transportation InstituteTest No. ..................................40516-13-1Date.........................................April 16, 2009

Test ArticleType.........................................Concrete BarrierName.......................................Single-Slope Barrier on 1.5H:1V SlopeInstallation Length...................100 ftMaterial or Key Elements........42-inch tall x 20 ft long single-slope

Soil Type and Condition...........Standard Soil, Dry

Test VehicleType/Designation.....................2270PMake and Model......................2002 Dodge Ram 1500 PickupCurb.........................................4630 lbTest Inertial..............................4953 lbDummy....................................No DummyGross Static.............................4953 lb

concrete barrier embedded 10 inches in soil in front of 1.5H:1V slope

Impact ConditionsSpeed....................................63.1 mi/hAngle.....................................24.2 degreesLocation/Orientation..............62 inch upstrm

Exit ConditionsSpeed....................................Out of viewAngle.....................................Out of view

Occupant Risk ValuesImpact Velocity

Longitudinal........................12.1 ft/sLateral................................24.6 ft/s

Ridedown Accelerations Longitudinal........................ -2.4 GLateral................................-11.3 G

THIV...................................... 29.6 km/hPHD....................................... 11.3 G

Max. 0.050-s Average Longitudinal........................ -6.5 GLateral................................-13.0 GVertical............................... -4.2 G

Joint 2-3

Post-Impact TrajectoryStopping Distance.........................247 ft dwnstrm

Vehicle StabilityMaximum Yaw Angle.....................-42 degreesMaximum Pitch Angle....................-11 degreesMaximum Roll Angle...................... 44 degreesVehicle Snagging...........................NoVehicle Pocketing..........................No

Test Article DeflectionsDynamic.........................................5.6 inchesPermanent.....................................5.5 inchesWorking Width...............................19.6 inches

Vehicle DamageVDS...............................................01RFQ5CDC...............................................01RFEW4Max. Exterior Deformation.............14.0 inchesMax. Occupant Compartment

Deformation.............................0.56 inches

10 ft fwd

FIGURE 7 Summary of results for MASH 08 Test 3-11 on the single-slope barrier on 1.5H:1V slope.

TABLE 1 Performance Evaluation Summary for MASH 08 Test 3-11 on Single-Slope Barrier on Slope

MASH 08 Evaluation Criteria Test Results Assessment

Structural AdequacyA. Test article should contain and redirect the vehicle or bring the

vehicle to a controlled stop; the vehicle should not penetrate,underride, or override the installation although controlled lateral deflection of the test article is acceptable.

Occupant RiskD. Detached elements, fragments, or other debris from the test

article should not penetrate or show potential for penetratingthe occupant compartment, or present an undue hazard to othertraffic, pedestrians, or personnel in a work zone.Deformations of, or intrusions into, the occupant compartmentshould not exceed limits set forth in Section 5.3 andAppendix E of MASH 08.

F. The vehicle should remain upright during and after collision.The maximum roll and pitch angles are not to exceed 75°.

H. Longitudinal and lateral occupant impact velocities should fallbelow the preferred value of 9.1 m/s (30 ft/s), or at least belowthe maximum allowable value of 12.2 m/s (40 ft/s).

I. Longitudinal and lateral occupant ridedown accelerations shouldfall below the preferred value of 15.0 Gs, or at least below themaximum allowable value of 20.49 Gs.

Vehicle TrajectoryFor redirective devices, the vehicle shall exit the barrier within

the exit box.

NOTE: Test agency: Texas Transportation Institute; test no.: 405160-13-1; test date: 4/16/2009.

Pass

Pass

Pass

Pass

Pass

Pass

Pass

Single-slope barrier in front of 1.5H:1V slope containedand redirected the 2270P vehicle. The vehicle did not penetrate, underride, or override the installation. Maxi-mum dynamic deflection during the test was 5.6 in.

No detached elements, fragments, or other debris were present to penetrate or show potential to penetrate theoccupant compartment, or to present undue hazard to others in the area.

Maximum occupant compartment deformation was 5.5 in.

2270P vehicle remained upright during and after the colli-sion event. Maximum roll was 44°.

Longitudinal occupant impact velocity was 12.1 ft/s, and lateral occupant impact velocity was 24.6 ft/s.

Longitudinal ridedown acceleration was −2.4 G, and lateralridedown acceleration was −11.3 G.

Vehicle remained within the exit box.

was judged to meet all the required impact performance criteria fora TL-3 impact.

SUMMARY AND CONCLUSIONS

The objective of this research was to develop a precast concretebarrier that can be placed adjacent to steep slopes such as 1.5H:1V,without using a concrete moment slab.

The final design incorporated 20-ft long precast single-slope barriersegments with grouted rebar grid connection. The 42-in.-tall single-slope barrier was preferred over other concrete barrier types becauseof the ease of embedment without requiring changes in the barrier’sprofile. Because the performance of the grouted rebar–grid connec-tion in a free-standing, single-slope barrier was not known underMASH evaluation criteria, the researchers evaluated its performanceusing a smaller scale bogie impact test and simulation analysis. It wasdetermined that the grouted rebar–grid connection did not provideenough strength to restrict lateral deflections. Results of the simula-tion analysis showed that large lateral deflection was expected withthe grouted rebar–grid connection when used with the single-slopebarrier in a free-standing mode.

The researchers then evaluated restricting the deflection of the bar-rier by embedding it 10 in. in soil. The barrier was placed in front of a1.5H:1V slope. The offset of the barrier from the slope break point ofthe soil embankment was restricted to 2 ft. Another phase of bogie test-ing and simulation analysis was performed to evaluate the performanceof the grouted rebar grid connection in the embedded barrier configu-ration. Results of the simulation analysis showed that the embeddedbarrier system will result in acceptably reduced lateral deflections.

A full-scale crash test was subsequently performed to validate thedesign. The embedded single-slope barrier in front of 1.5H:1V slopeperformed acceptably according to the requirements of MASH. Thepermanent lateral deflection of the barrier was 5.5 in.

The embedded single-slope barrier application developed in thisresearch is expected to result in significant cost savings for the usertransportation agencies. The benefit of this application comes fromthe elimination of the use of a moment slab to restrict lateral barrierdeflection. The cost of constructing and installing the single-slopebarrier with a moment slab is typically $375 per linear foot (on thebasis of recent bids received by Washington State Department ofTransportation). The cost of constructing and installing the embed-ded single-slope barrier is approximately $75 per linear foot (on thebasis of test article construction in this research). This implies a cost

Sheikh, Bligh, Albin, and Olson 129

saving of nearly 80%. In addition, the use of a precast barrier mini-mizes the amount of time to construct in traffic, which reduces traf-fic disruptions and worker exposure. Eliminating the moment slabfurther reduces time by eliminating a construction phase.

In comparison to some of the metal guardrail systems developedfor use on slopes, the initial cost of installing the embedded singleslope barrier will be higher. However, because of its small perma-nent deflection, the embedded barrier design is expected to requirelittle or no maintenance under most vehicle impacts. Because metalguardrail systems require significant repair time and cost, the embed-ded barrier design developed in this research is expected to result insignificant life-cycle cost savings in areas where frequent vehicle hitsare encountered.

ACKNOWLEDGMENTS

This research was performed under a Pooled Fund program betweenthe state of Alaska Department of Transportation and Public Facilities,California Department of Transportation, Louisiana Department ofTransportation and Development, Minnesota Department of Trans-portation, Tennessee Department of Transportation, Texas Departmentof Transportation, and Washington State Department of Transporta-tion, and FHWA. The authors acknowledge and appreciate theagencies’ guidance and assistance.

REFERENCES

1. Polivka, K. A., R. K. Faller, D. L. Sicking, and J. R. Rohde. W-BeamGuardrail Adjacent to a Slope. In Transportation Research Record: Jour-nal of the Transportation Research Board, No. 1743, TRB, NationalResearch Council, Washington, D.C., 2001, pp. 80–87.

2. Manual for Assessing Safety Hardware. AASHTO, Washington, D.C.,2008.

3. Beason, W. L., H. E. Ross, Jr., H. S. Perera, W. L. Campise, and D. L.Bullard, Jr. Development of a Single-slope Concrete Median Barrier.Texas Transportation Institute, College Station, 1989.

4. Sheikh, N. M., R. P. Bligh, and W. L. Menges. Development and TestingOf a Concrete Barrier Design for Use In Front of Slope or on MSE Wall.Report 405160-13-1. Texas Transportation Institute, College Station, 2009.

5. Ross, H. E., Jr., D. L. Sicking, R. A. Zimmer, and J. D. Michie. NCHRPReport 350: Recommended Procedures for the Safety Performance Eval-uation of Highway Features. TRB, National Research Council, Wash-ington, D.C., 1993.

The Design Section peer-reviewed this paper.