California Department of Transportation

Development of Weed Control Barrier Beneath Metal Beam Guard Railing


Weed growth beneath metal beam guardrail (MBGR) systems is unsightly and provides the starting point for large brush or wild land fires. Caltrans currently uses herbicides, mechanical methods, or asphalt concrete to control weeds beneath the metal beam guardrail.

Caltrans District 2 Maintenance Engineer Salvador Torres, Jr. developed a non-proprietary product and dubbed it CRMCrete because it is comprised of concrete with recycled scrap tire crumb rubber. Crash testing of the product was needed in order to determine whether this product could be placed beneath MBGR to prevent weed growth yet still allow the guardrail posts to move as needed for system compliance with NCHRP Report 350 Test Level 3 criteria for longitudinal barriers.  Use of this product is expected to lower costs, increase durability, reduce worker roadside exposure and provide environmental alternatives for disposal of scrap tire rubber.  

Development of the Weed Control Barrier

Six posts were built for Bogie testing prior to construction of a full barrier.  Two posts were constructed without weed control barrier to establish a baseline for post performance. Additional post configurations (two each) were constructed with weed barrier control. Based on the results of the Bogie tests, a full-scale vehicle test was conducted. Rollover of vehicle in Test 658 required a slight redesign of the weed barrier. A 193.25 foot section of MGBR with steel posts was constructed at the Caltrans Dynamic Test Facility. The barrier design for Test 659 is shown in Figure 1.

CRMCrete Configuration
Figure 1. CRMCrete Configuration

Type 90 Detail
Concrete Pour

Type 90 Bridge Rail Front
Close-up of Barrier

Type 90 Back
Completed Barrier End

Type 90 Back of Post Close-up
Completed Barrier


Impact Conditions

Test 652
Vehicle: Bogie
Impact Speed: 33.1 km/h

Test 653
Vehicle: Bogie
Impact Speed: 32.0 km/h

Test 654
Vehicle: Bogie
Impact Speed: 34.4 km/h

Test 655
Vehicle: Bogie
Impact Speed: 33.6 km/h

Test 656
Vehicle: Bogie
Impact Speed: 34.3 km/h

Test 657
Vehicle: Bogie
Impact Speed: 34.6 km/h

Test 658 (NCHRP Report 350 Test 3-31)
Vehicle: 1988 Chevrolet 2500 ¾ Ton Standard Cab Pickup
Impact Speed: 99.8 km/h
Impact Angle: 25.8°

Test 659 (NCHRP Report 350 Test 3-31)
Vehicle: 1994 Chevrolet 2500 ¾ Ton Standard Cab Pickup
Impact Speed: 99.5 km/h
Impact Angle: 24.3°

High-speed Crash Test Videos

Test 659
Tower Upstream
Tower Downstream

Related Documents and Links

Contact Information

David Whitesel
Project Engineer

John Jewell
Senior Engineer

Bob Meline
Senior Engineer