Roadside Safety at WSDOT

General Information
Roadside safety is an important component of total highway design that addresses the area outside the roadway. As described in the WSDOT Design Manual, an intentional approach to roadside design can reduce the severity and subsequent consequences of a vehicle roadside encroachment. Whenever possible, a designer should design relatively flat, unobstructed roadsides to provide a forgiving environment to an encroaching vehicle. However, designing clear, flat, roadside areas is not always feasible as projects may have competing needs and tradeoffs to consider. Some different factors that may compete with providing a clear, flat roadside area include existing topography considerations, right of way constraints, environmental constraints, or other various facilities and project needs.

State roadside safety policies and guidance are provided for designers in Division 16 of the WSDOT Design Manual. Before using these chapters, designers need to see WSDOT Design Manual Chapter 1105 (pdf 127 kb) (for Improvement projects) or Chapter 1120 (pdf 97 kb) (for Preservation projects) to determine what kind of roadside safety design and analysis are required on your project.

  • Chapter 1600 Roadside Safety (pdf 678 kb) addresses the area outside of the roadway and is an important component of total highway design. Guidance on fundamental roadside safety issues is presented in this chapter including clear zone, mitigation approaches, medians, rumble strips and rumble stripes, other roadside safety features, and other related topics.
  • Chapter 1610 Traffic Barriers (pdf 1.2 mb) describes the design and use of traffic barrier, terminals, and transitions that are approved for use by WSDOT. Topics include guardrail, cable barrier, concrete barrier, bridge traffic barriers, terminals and transitions, other barriers, and other related topics.
  • Chapter 1620 Impact Attenuators (pdf 1.8 mb) describes the design and use of impact attenuators that are approved for use by WSDOT.

There are standard specifications and special provisions related to roadside safety hardware that designers and others should be aware of including the following:

Please note that there are many other pertinent specifications and GSPs referencing roadside safety that are not shown in the list above but also commonly apply to projects.  

You can use the applicable standard specification or GSP to search the WSDOT Qualified Products List to determine which roadside safety related proprietary devices are available to meet your design requirements. This list is kept updated by the WSDOT Design Office and Materials Lab through correspondence with manufacturers, particularly with respect to WSDOT’s ongoing effort to implement MASH compliant roadside safety products.

Design Bulletins about roadside safety are occasionally issued to provide clarification or additional guidance for certain situations or projects types. They are normally provided between manual updates, and eventually incorporated into the WSDOT Design Manual or retired depending on the topic. See the Roadside Safety questions and answers (docx 22 kb) that specifically addresses emergent questions in roadside safety.

MASH Implementation
The Manual for Assessing Safety Hardware (MASH) updated the testing criteria for crash testing roadside hardware. The WSDOT Design Office policy staff are responsible for developing the criteria, guidance, and policies related to MASH transition for design. This work includes criteria for the acceptance and design of MASH compliant roadside safety hardware. WSDOT’s transition to MASH is organized by the Design Office according to stipulations provided in the AASHTO-FHWA Joint Implementation Agreement for MASH.

The transition to MASH is organized by hardware product category. Expect to find updates to the WSDOT Design Manual, Standard Specifications, GSP’s, Standard Plans, and Qualified Products List over time that reflects this transition. Although the last official MASH implementation date has passed, the transition to MASH for some roadside safety hardware product areas continues. Recent direction from FHWA and AASHTO—recognizing that not all roadside safety hardware is MASH compliant at this time—is allowing non-MASH compliant hardware to be installed in certain circumstances. The following links provide information that may be useful for designers.

Length of Need
Length of need refers to the total length of longitudinal barrier needed to shield a non-crashworthy, fixed object or feature. A length of need calculation is commonly required to determine the configuration of any barrier regardless of type. The length need calculation spreadsheet (xls 20 kb) may be used when calculating the required length of need for a barrier. See WSDOT Design Manual Section 1610.03(5) (pdf 1.8 mb) for more information.

Type 31 Beam Guardrail
Type 31 beam guardrail is used in all new installations except in certain circumstances (see (Old) Type 1 Beam Guardrail section below). All beam guardrail systems require either an anchor or crashworthy terminal at their endpoints. In general, a crashworthy terminal is used when a guardrail end is located inside the Design Clear Zone (see WSDOT Design Manual Section 1600.02 (pdf 615 kb)) and can be struck head on by a vehicle. An anchor is allowed when the guardrail end is located outside the Design Clear Zone or inside the Design Clear Zone and not subject to head-on impacts (i.e. trailing ends of guardrail runs on one-way roadways). The WSDOT Beam Guardrail Type 31 Buried Terminal Type 2 (Standard Plan C-22.16) is the preferred guardrail terminal since the end of the guardrail run is buried and not subject to head-on vehicle impacts. Shop drawings and additional information about designing and identifying guardrail terminals and anchors from different manufacturers.

(Old) Type 1 Beam Guardrail
Type 1 guardrail is no longer used in new installations except in intersection radius designs. A primary reason for phasing out Type 1 guardrail is that all configurations of the Type 1 guardrail are not MASH- compliant (pdf 139 kb) whereas Type 31 guardrail is MASH compliant.

(Old) Type 1 Beam Guardrail Placement Cases (Removed from Design Manual in 2017) (pdf 140 kb)
(Old) Type 1 Beam Guardrail Terminals and Anchors (pdf 111kb)
(Old) Type 1 Beam Guardrail Transitions (pdf 146 kb)

When an intersection radius is needed in new construction, it is permissible to use either one of the (Old) Type 1 designs (Placement Case 12 or 13, (pdf 140 kb) or the Guardrail Placement Strong Post Type 31 Intersection Design (Standard Plan C-22.42. See the Plan Sheet Library for Type 1 weak post intersection design plans.

Type 20 and Type 21 Guardrail
Type 20 and Type 21 guardrail are primarily used in conjunction with Service Level 1 bridges. Type 20 and Type 21 guardrail are TL-2 systems appropriate for speeds 45 mph or less.

See Type 1 Placement Case 14 (pdf 140 kb) for use on Service Level 1 bridge retrofit rail systems. Type 20 guardrail is used on the approach and no transition is needed between the Type 20 guardrail and the Service Level 1 bridge rail since they are both weak post systems. A Type 6 transition is used when connecting the Type 20 to a strong post guardrail or a terminal. See the Plan Sheet Library for more information about these designs.

Contact Bridge and Structures Office for more information about Bridge Service Level 1 retrofits.

Cable Barrier
All cable barrier systems that are available for use in new construction are proprietary. New construction requires the 4-strand versions of these systems. See WSDOT Design Manual Section 1610.05 (pdf 1.3 mb) for more information.

Concrete Barrier
Concrete barrier is available in either precast or cast-in-place configurations. Precast barrier may be anchored or unanchored according to project requirements and desired deflection characteristics (see WSDOT Design Manual Section 1610.03(3) (pdf 615 kb)). High Performance concrete barrier, which are taller, are available for use when required in certain situations (see WSDOT Design Manual Section 1610.03(1)(b) (pdf 1.3 mb)).

Versions of these concrete barrier designs are available with drainage scuppers along the base and may be specified where drainage has to pass through the barrier run. Standard plans for scupper barrier are in development and are planned to be available in September 2021. In the meantime, scupper concrete barrier details are available for incorporating into PS&E packages on a project-by-project basis. Contact HQ Design for more information about scupper barrier, and see WSDOT Design Manual Section 1610.06 (pdf 1.3 mb) for more information about concrete barrier.

Impact Attenuators
Impact attenuators are protective systems that prevent or reduce the severity of head-on impacts with an object or feature by either gradually decelerating the vehicle to a stop when hitting the attenuator head-on, or redirecting the vehicle away from the object or feature when struck on the side. These systems are used for rigid objects or other features that cannot be removed, relocated, or made breakaway.  All impact attenuator systems are proprietary items. Use the attenuator selection template (docx 22 kb) to determine which products are available to meet your project specific constraints.

See WSDOT Design Manual Chapter 1620 (pdf 1.8 kb) for more information on impact attenuators and for links to impact attenuator product documents that may be needed for the design at the impact attenuator location (i.e. attenuator foundation requirements, or other).

If you have any comments or questions, please contact the HQ Design Office:
Tim Moeckel, PE
Roadside Safety Engineer
Ph: 360-704-6377
Fax: 360-705-6815