Selection, Installation and Maintenance of W-Beam Guardrail End Terminals

This brief provides essential guidelines for selecting, installing, and maintaining W-beam guardrail terminals. It also highlights common concerns associated with these components and presents widely accepted practices to tackle these issues. For further reference, the American Association of State Highway and Transportation Officials (AASHTO) Roadside Design Guide, 4th Edition, Chapter 8.3 offers comprehensive insights into terminal design principles.

With competitive pricing and prompt delivery, DACHU aspires to be your preferred supplier and partner.

Choosing the Right Terminal

Currently, there are three primary designs for W-beam guardrail end terminals: Burke-in-backslope, non-energy-absorbing, and energy-absorbing. Understanding the behavior of these terminals under impact is crucial. For instance, Figure 1 illustrates how vehicles react when colliding with non-energy-absorbing and energy-absorbing terminals at high speeds (62 mph). The choice between an energy-absorbing terminal and a non-energy-absorbing terminal should be made based on the likelihood of a near end-on impact and the characteristics of the recovery area directly behind the terminal.

Figure 1: Vehicle Trajectories by Terminal Type

Features of Various Terminal Types

1. Non-Energy Absorbing: This type of terminal does not significantly dissipate kinetic energy during a head-on impact and serves as a gating system that allows the vehicle to pass through the area adjacent to the guardrail. Key features include:

   • Minimal reduction in vehicle speed during near head-on impacts
   • Possible run-out distances exceeding 150 feet
   • Most effective in locations with extensive, traversable areas behind the guardrail, such as wide freeway medians

2. Energy Absorbing: This terminal effectively dissipates substantial kinetic energy during head-on collisions. Notable characteristics include:

   • Required for installations under 150 feet from any shielded object
   • Can halt an impacting pickup truck within approximately 50 feet in a head-on collision
   • Ideal for areas with limited clear zones behind the terminal or regions containing fixed object threats

3. Buried-in-Backslope: This terminal integrates the W-beam guardrail installation by burying the end into a backslope. Proper grading is vital as the terrain leading to the buried section must allow vehicle traversal without presenting hazards. Designers must consider various grading specifications:

   • The backslope must be steep enough to prevent vehicles from surmounting the rail
   • The barrier flare rate must complement roadway design speed and traffic volume
   • The guardrail height must consistently relate to the roadway edge until it crosses the ditch flow-line
   • W-beam rub rails must be used if the distance from the base of the primary rail to the ground exceeds 17 inches.

Figure 2 serves as a foundational flowchart for designers to determine the most suitable terminal for specific locations. It’s essential to begin with a verification of the need for a barrier and confirm the proper length of need. For barriers shorter than 150 feet, an energy-absorbing terminal selection is advisable. Additionally, when a feasible backslope exists near the terminal, the buried-in-backslope option should be evaluated. Otherwise, non-energy-absorbing or energy-absorbing terminals may be suitable based on site conditions.

Figure 2: Terminal Selection Flow Chart

As you consider terminal selection, be aware of common issues and adopt generally accepted practices to facilitate effective installation:

Side-by-Side Terminals:
When two barriers are within seven feet of each other, they should be combined and terminated as either a median barrier or a bullnose design to minimize the risk of vehicles encountering hazards.

Curbs:
Curbs can destabilize vehicles upon contact with terminals; thus, their presence should be reduced or avoided if possible. Any added components should comply with the original design to ensure optimal terminal performance.

Are you interested in exploring further about Hot Dip Galvanized W-Beam Guardrail? Contact us today for an expert consultation!

Terminal Installation:
Prior to installation, the manufacturer's manual should be adhered to meticulously. The grading surrounding the terminal is critical, as terminals receive crashworthiness testing under flat, unobstructed conditions. Key grading zones of concern include:

1. Advance area
2. Adjacent area
3. Run-out area

Each of these areas must be carefully evaluated during the design phase. Proper earthwork and grading specifications are necessary to achieve successful terminal performance. Moreover, essential earthmoving must be finalized before safety feature installation.

Figure 3: Terminal Grading Areas

Terminal Maintenance:
The Roadside Design Guide categorizes maintenance routines into three segments: (1) routine maintenance, (2) crash maintenance, and (3) material and storage standards. Routine maintenance requires regular inspections of roadside devices to assess condition and identify needed repairs, ensuring proper materials are stored for effective maintenance work.

In light of the aforementioned guidelines and practices, incorporating robust training, certifications, and engineered earthwork design in construction plans can significantly improve the efficacy of W-beam guardrail installations. Ensuring optimal performance through attentive maintenance and installation practices leads to enhanced roadside safety.

For further inquiries, please visit Galvanized Highway W Beam Guardrail.