Jul. 28, 2025
KYTC currently uses Midwest Guardrail System (MGS) for new installations of standard guardrail and corresponding end treatments. MGS is a non-proprietary steel or wood post W-beam guardrail system that meets MASH Test Level 3 criteria. The system adopts a typical W-beam guardrail with the following characteristics:
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• 31-inch top of rail mounting height and tolerance of +/- 1 inch (see Section 3.5, Guardrail Height).
• Minimum 6-foot-long W6 x 9 steel posts or 6-inch x 8-inch wood posts
o Longer posts may be used (e.g., 7 feet or 9 feet) (see Section 5.1, Strengthening Guardrail).
• 6 inch x 8 inch routed or non-routed wood or composite plastic offset blocks
• Mid-span rail splices
o MGS relocates the splice (weakest link) away from the highest stress point at the post and blockout.
For MGS installations, contractors must use W-beam panels that are 12 feet 6 inches or 25 feet in length, but they may employ a 6-foot 3-inch panel at the end of the run.
Prior to the standard guardrail in Kentucky was the strong-post W-beam. It consists of wood or steel posts that support a W-beam rail element blocked out from the posts. Blockouts are typically made of timber or composite plastic and are 6 or 8 inches deep and 6 inches wide. The strong-post W-beam meets NCHRP 350 Test Level 3 criteria and was mainly used before the adoption of MASH testing criteria. Strong-post W-beam guardrail systems have been installed at different heights, ranging between 27 to 29 inches.
Although the Cabinet has adopted MGS for all new installations, many miles of strong-post W-beam barrier have been installed based on previous NCHRP 350 guidance. Many of these systems have and should continue to have acceptable real-world performance. Raising all existing guardrail systems to meet current criteria is neither cost-effective nor practical. KYTC maintenance crews will continue to maintain strong-post W-beam guardrail systems until they reach the end of their service lives.
Other approved guardrail types may be used on Kentucky highways. Examples of alternative guardrail systems include the weak post W-beam, Weathering Steel Guardrail, and Steel Backed Timber Guardrail. If an alternative guardrail is utilized, it should be appropriate for the road context. Use of an alternative guardrail system requires written justification. The Division a project originates in — Division of Highway Design or Division of Maintenance — is responsible for reviewing and approving the use of alternative guardrail systems.
Contractors that install a temporary guardrail during construction must comply with construction requirements for permanent guardrail.
See the HKP article, Roadside Safety (coming soon), for a discussion of barrier warrants.
The LON is the length of barrier required to adequately shield the object or area of concern and prevent a vehicle from reaching the shielded feature. The length of guardrail must be sufficient to properly shield the object or area of concern, which is critical for roadside safety. See the HKP article, Roadside Safety (coming soon), for a discussion of LON.
During project design, the designer determines whether to install guardrail and calculates the LON. The LON is then used to lay out the guardrail system, and the designer notes on the plans where to install guardrail. If possible, designers should take steps such as flattening slopes with excess earthwork material (where field conditions allow) to reduce the need for guardrail. Refer to KYTC’s Standard Drawings and to AASHTO’s Roadside Design Guide guidance on lateral offsets, barrier deflection, terrain effects, flare rates, and LON.
KYTC measures guardrail quantity in linear feet. The distance is measured along the actual length of the rail between the limits of end treatments, terminal sections and bridge end connections, and crash cushions. Shop curved guardrail is measured in linear feet at 1.3 times the actual length.
Designers commonly design guardrail in to the nearest 12-foot-6-inch or 25-foot increment. A 6-foot-3-inch increment may be used if needed. Field conditions often differ from what plans depict, which can in turn affect the quantity of guardrail needed. Construction Engineers have the final responsibility for determining the placement and installed length of guardrail. A best practice for designers is to slightly overestimate guardrail length so that any construction field adjustments result in a negative-cost change order.
During construction, a guardrail is constructed to the alignment and at the locations shown in the Contract. Sometimes field conditions require that the amount and location of installed guardrail be adjusted. Before ordering guardrail materials, the Engineer and Contractor should meet on the job site to verify the LON and end treatment locations designated in the plans are appropriate for the field conditions. Adjustments should be made as needed. The LON, final location, and end treatment types are approved by the Construction Engineer.
Where possible, construction personnel should flatten earth-fill slopes using excess fill material to attain a clear zone and remove or minimize the need for guardrail. When laying out guardrail field installations, the Engineer should consult with the Roadway Designer when questions arise.
A guardrail installation should have a minimum length of 200 feet (including the end treatments) as this ensures adequate tensile strength for the system to perform well. In some cases, field conditions may warrant a shorter installation, which is acceptable. In these cases, consider strengthening the guardrail (see Section 5.1, Strengthening Guardrail). Similarly, if a guardrail will be installed prior to a fixed object, minimum guardrail length (including end treatments) should be 200 feet. Again, this length may be reduced if field conditions warrant.
Avoid short gaps between two guardrail installations. If connection gaps between barrier termini are less than 200 feet, the installations should be connected as a single run. Installing additional guardrail will be easier to maintain and less expensive than two end treatment installations. Exceptions may be necessary to provide access to locations behind the guardrail (for mowing and other maintenance tasks) or for other project considerations.
Guardrail system performance is tied closely to the height of the W-beam rail element. Installation height is computed by taking a measurement at the center of the rail, at the bolt. Here, the height is measured from either the pavement surface, theoretical pavement, nominal terrain, or gutter pan to the top of the rail. A guardrail should be installed to the true gradient with no sags.
The method used to measure guardrail height varies based on guardrail location. Five scenarios and their corresponding methods are described on the following page.
To give vehicles sufficient opportunity to recover without impacting an obstacle, place guardrail as far away from the traveled way as practical. Typically, guardrail is installed in the shoulder 2 feet from the slope break hinge point (see Section 3.10, Soil Backing). Narrow shoulders are often widened to facilitate guardrail placement.
The usable shoulder is the width available for vehicles to make an emergency stop or parking stop. The graded shoulder is distance from the edge of the travel lane to the normal slope break. Unless guardrail is present, typically the graded shoulder width is equal to the usable shoulder width. Once the usable shoulder width is established for a project and the decision has been made to install guardrail, the graded shoulder will need to be widened 3 feet 5 inches beyond the usable shoulder width to accommodate the guardrail installation. With the guardrail’s face located along the outside of the usable shoulder, the additional graded width provides 2 feet of soil backing behind the guardrail posts. If installing 2 feet of graded shoulder behind the posts is impractical, longer guardrail posts can be utilized.
For a discussion of shoulder width and slope, see the HKP article, Roadway Design Elements (coming soon).
Do not install guardrail posts in structural pavements that will restrict post movement during impact.
In some cases, guardrail may be installed closer to an obstacle rather than at the roadway shoulder edge. Installations of this type reduce the length of rail needed to shield the obstacle. Placing guardrail farther from the roadway lessens the probability of a vehicle impact. At the same time, when a vehicle strikes a guardrail it may have a higher encroachment angle. This is an undesirable condition.
Lateral placement of guardrail away from the shoulder edge is most applicable when small areas of concern are present (e.g., point-type obstacles such as overhead sign bridge supports and bridge piers).
Carefully select where to place guardrail installations on earthen terrain slopes. Judicious positioning will minimize the likelihood of an errant vehicle vaulting over a guardrail and improve the guardrail’s performance. MGS can be placed at any position on a slope (relative to the slope only) if the slope in front of the barrier is flat (i.e., 10:1 or flatter). This also applies to areas in front of the flared section of guardrail and the area approaching terminal ends.
Guardrail should not be placed on a steep slope. For slopes steeper than 10:1, see the HKP article, High-Tension Cable Barrier (coming soon).
While the use of curbs with guardrails is discouraged, curbs more than 6 inches in height should not be used with guardrail. By themselves, curbs typically cannot redirect vehicles, except for very low speed impacts. Placing a curb near guardrail can result in a vehicle vaulting over the barrier. The following guidance can assist in planning curb type and guardrail placement when the use of guardrail/curb combinations is unavoidable:
• For design or posted speeds of 45 mph and less:
o Construct the guardrail so its face is flush with the curb’s face. Avoid locating a curb in front of a guardrail. Consider reducing the curb height to 4 inches and stiffening the rail to reduce vaulting potential. (see Section 5.1, Strengthening Guardrail).
o If it is not practical to install the guardrail flush with the face of the curb, construct the guardrail with a minimum offset of 6 feet from the curb’s face to the guardrail’s face.
• For design or posted speeds greater than 45 mph:
o Facility designs should omit curbs. However, a mountable curb may be used at the edge of the shoulder if necessary. If guardrail is needed in this situation, construct it so the rail’s face is flush with the curb’s face.
Occasionally a guardrail system must be strengthened to reduce the design deflection distance. For example, a transition section is needed where a guardrail attaches to the approach end of a rigid concrete bridge rail (See the HKP article, Barrier Classifications (coming soon)). A guardrail must be stiffened if a rigid object obstacle is present within the design deflection distance. Standard installations can be modified using the following techniques to strengthen the guardrail:
• Add a rubrail
• Install additional posts (reducing the post spacing) (See MGS Working Width Table in Section 3.11.)
• Use extra length posts (e.g., 7-foot or 9-foot posts, not the standard post length of 6 feet)
• Use thicker gauge posts (e.g., 10-gauge posts instead of 12-gauge posts)
• Double nest the rail
• Bolt a W-beam to back of the posts
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Featured content:For extra length posts and nested guardrail, quantities should be measured and bid items provided. Consult Section 719 of the Standard Specifications for Road and Bridge Construction for additional information. Where extra strength is needed different methods may be combined (e.g., when the area of concern is near the back of rail).
A guardrail is classified as a semi-rigid barrier due to its deflection distance upon crash impact (see the HKP article, Roadside Safety (coming soon), for a discussion on barrier categories). A transition section is needed when a guardrail connects to a rigid barrier (e.g., bridge railing or concrete barrier) or rigid object (e.g., bridge pier or sign structure). The transition should provide a gradual, continuous stiffening of the guardrail system from a less rigid to more rigid system. This reduces or prevents a vehicle from snagging or punching through the barrier. Use of a cast-in-place anchor or through-bolt connection is recommended to ensure the connections are as strong as the barrier itself.
Use TL-2 or TL-3 Thrie-Beam Guardrail Transitions to connect W-beam guardrail to concrete bridge rails, rigid barriers, or rigid objects. The TL-2 railing transition should be used when speeds are 45 mph or less. The TL-3 railing transition must be used when speeds are over 45 mph. For more details, see Standard Drawings Nos. BHS-013 and BHS-014.
Historically, the Guardrail Connector to Bridge End Type A was used on both bridge ends on undivided highways and on the approach bridge ends of divided highways. A Guardrail Connector to Bridge End Type A1 was used on the exit bridge ends of divided highways. A Guardrail Connector to Bridge End Type D was applied on each end of a bridge on which a sidewalk was present or its installation was proposed on the structure (and not on the roadway). This only applied to rural structures having two-direction traffic with a sidewalk.
Type A, A1, and D connectors are no longer installed on new highway construction. When repairing or restoring existing concrete barrier wall and these guardrail connectors, see Standard Drawings RBC-004, RBC-005, RBC-05N, and RBC-006. Refer to the RBB and RBC series of Standard Drawings in the HKP article, Bridge Railings and Transitions (coming soon), for more details.
On some retrofit projects use of standard guardrail connectors may not be appropriate. Contact Central Office Division of Maintenance for guidance.
Delineators must be installed on new guardrail. Standard Drawing No. RBR-055 (Delineators for Guardrail) illustrates delineator elements, placement, and spacing. Section 830 of the Standard Specifications addresses retroreflective requirements for guardrail delineators.
The District is responsible for deciding (1) whether to install new delineators on existing guardrail systems which lack delineation or (2) whether it is necessary to replace existing guardrail delineation due to non-reflective and/or missing delineators. High-priority locations for guardrail delineation include curves and ramps on freeways and expressways, as well as guardrail sections located in the median. The District may elect to place delineation to indicate openings at entrances on highways.
Where a guardrail end treatment adjacent to the roadway is marked, a Type 3 object marker is typically used. Alternating stripes of Type 3 object markers should slope downward, toward the side on which traffic is to pass. Generally, the end treatment manufacturer supplies Type 3 object markers. Use retroreflective sheeting that conforms to the size of the approach end.
Double-faced guardrail has two W-beam rails configured as a single beam on each side of post. It is typically used in the median in place of concrete barriers, particularly when the required shielding length is relatively short. Double-faced guardrail is also used when a guardrail may be exposed to impacts from either side. When installed near the pavement edge, it is critical for the area between the posts to be free of asphalt.
On longitudinal guardrail installations, double blockouts (up to 16 inches deep) may be used to increase the post offset to avoid obstacles such as curbs. There is no limit on the number of posts that can have double blockouts installed.
Do not employ double blockouts for transitions and terminals, unless approved by the manufacturer. Under special circumstances (e.g., avoiding buried obstacles that are not relocated), additional blockouts may be installed to obtain up to 24 inches of clearance (three 8-inch blockouts or two 12-inch blockouts) for one or two posts in a section of guardrail. Standard Drawing RBR-031 (Guardrail End Treatment Type 3 Pipe Drainage Detail) offers an example of using extra blockouts.
Omit a post only under special circumstances and only on a standard run of guardrail. Omitting a post requires the construction engineer’s approval.
Single posts may be omitted along runs of MGS W-beam guardrail without the system needing modification (i.e., no weakened posts, no nested rail elements, no special posts). Always consider the following issues before taking this step:
1. At least 50 feet is required between omitted posts, a terminal, or other special design.
2. Omitted posts cannot be used within transitions, terminals, or special designs.
3. No curbs are present where guardrails are installed.
4. Additional deflection resulting from the omitted post.
Occasionally, an intersecting side road or driveway is located so close to a side obstacle that installing a minimum length MASH TL-3 guardrail is infeasible. This most occurs often at bridge ends. A short radius curved guardrail installation may accommodate this situation. See Standard Drawing RBI-001 for more details.
Keep the following in mind when designing a short-radius curved guardrail:
• Installations at intersections and driveways can create nuisance hit problems for turning traffic (e.g., tractor trailers turning off of or onto side roads, farm implements turning into and out of field entrances). Check turning patterns to ensure a guardrail installation will not significantly affect turning movements.
• Installations at intersections and driveways can obstruct motorist sight, especially if the side road or entrance is at or near the crest of a vertical curve. Perform sight distance analysis for both plan and profile views to determine what effects guardrail installation may have on motorist line-of-sight.
On roadways where the design speed is between 30 and 45 mph and there is a curb adjacent to the traveled way (e.g., urban and suburban roadways), keep the border area free of obstacles. Any decision to use a guardrail within the border area should be informed by careful evaluation. A guardrail used in the border area should present less of a hazard than the obstacle it shields. See Chapter 10 of AASHTO’s Roadside Design Guide for further guidance on clear zones in urban areas.
Use the appropriate omitted-post design (as discussed above) if rock is present where a single guardrail post is to be installed. If rock is present at several points where posts will be installed, place the posts in cored holes (see Section 719.03.01 of the Standard Specifications for Road and Bridge Construction).
When shales are used in embankment fill sections, acidic shale is generally encased inside the embankment. At least 4 feet of nondurable shale or clay soil should be placed atop the embankment to control the corrosion of guardrail posts. It may be appropriate to install corrosion-resistant guardrail posts. See Special Note 8N Corrosion Resistant Guardrail and the Geotechnical Guidance Manual GT-609-5 on Acid-Producing Shales.
Horizontal lagging walls are often used for temporary or permanent retention of soil material and other backfill. Lagging may consist of wood, guardrail, or geogrid. When backfill is placed or compacted behind the guardrail wall, it is imperative that rails not to be damaged.
Lagging has traditionally been designed based on experience or empirical methods. (e.g., the Federal Highway Administration uses the Goldberg Zoino chart). Contact the Geotechnical Branch for more information.
When launching a project with respect to guardrails for highways, it is necessary to think of many crucial things in terms of safety, durability, and economical installation. Here’s a detailed guide to help you make an informed decision:
AASHTO Compliance: It is very important that the guardrail system is constructed according to or above the set standards laid down by the American Association of State Highway and Transportation Officials (AASHTO). The higher the compliance, the better the crashworthiness and performance.
RehumanizeLocal Regulations: Ensure that you always confirm whether the guardrails conform to any such regulations that are more specific to your locality or country. Local compliance is as crucial as national standards.
RehumanizeCrash Testing Data: Ask the manufacturer to provide you crash testing data. This data contains pieces of information about how the guardrail behaves in the real world, showing that it can ensure safety, and besides, it presents some other aspects of safety.
Steel Type: Choose galvanized steel, which is used as the standard for corrosion resistance, for the production of guardrails. For the very hazardous environmentally, a very hot-dipped galvanized steel one, will withstand it best.
RehumanizeCoating Thickness: The thickness of the protective coating is paramount for the long-term durability and the weathering resistance. Make sure the coating is thick enough for your weather conditions.
RehumanizeMaterial Certifications: Material certifications must be tor-tified to clear the quality and standards of the steel used. This aspect makes sure that the quality of the materials is well sustained.
Guardrail Profile: The guardrail profiles include W-beam, box beam, and Thrie-beam, which possess different levels of deflection and impact absorption. Pick the appropriate profile per your road design and the traffic speed.
Post Spacing: Establish the proper post spacing of the guardrail system according to the site conditions. In most cases, spacing is close to one another, which strengthens the structure and improves its performance.
RehumanizeEnd Treatments: Appropriate end treatments are advisable to redirect the vehicles safely in case of a collision. This aspect is most important for the reduction of the injury and damage.
Post Type: Do not forget to address the kind of posts needed for your guardrail system e.g., H-posts, C-posts. You may pick the kind that suits your installation environment and specific needs.
Anchoring Methods: Choose the best anchoring method be it concrete or ground anchors depending on soil conditions and project requirements.
RehumanizeInstallation Expertise: Make sure you have qualified installers who are capable of adhering to the specifications accurately and have the system installed correctly.
Total System Cost: Before making a comparison of the alternatives, include the cost of the guardrail, posts, hardware, end treatments, and installation in the total cost. This crosswide cost assessment is useful in budget planning.
RehumanizeMaintenance Requirements: Select a system that needs little to no maintenance. Better quality of materials and the coatings can greatly reduce the repair cost over the years.
RehumanizeExperience and Track Record: Highway safety manufacturers different but their best ones are those which are reputable and have proper experience and track record to prove that they are able to design and produce safety products. Their knowledge may act as a warranty for the durability of their products.
Product Warranties: Ask about any warranties that come with the product. Find out if the warranties include defective or performance problems.
RehumanizeTechnical Support: They should make sure to give you some technical help if necessary, and do this by reference guide or any paperwork where you can find answers for your questions. This aid becomes especially important if the project requires any installation instructions or solving difficulties that may come about during the execution.
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