FAQ - Frequently Asked Questions
SKT Wood and Steel Post System – Tangent W-Beam Terminal
- Can the SKT roadside terminals be used on a left shoulder if the shoulder is a median for oncoming traffic?
- Can 6'-0" long steel foundation tubes without soil plates be used at SKT posts #3 through #8?
- Can standard hex bolts be used to attach the cable anchor bracket to the SKT guardrail end section?
- The SKT-SP (Standard Post) system is sometimes called out as 12'-6" long. Is that allowable?
Yes, provided the distance from the exit slot of the terminal to the edge of the pavement for the oncoming traffic is at least 25 feet. Studies of many accidents have shown that a lateral distance of 20 feet was the effective maximum distance that any component of a damaged tangent terminal came to rest. The recommended 25-foot distance has a 5-foot safety factor. In addition, the proper Length-of-Need must be established.
No. The 6'-0" long steel foundation tubes without soil plates may only be used at SKT posts #1 and #2. If foundation tubes are used at SKT posts #3 and #4 or at #3 through #8, they must be the 4'-6" long foundation tubes. The soil plates for these short tubes at posts 3 through 8 are now optional. The 4'-6" long foundation tubes with soil plates may also be used at SKT post #1 and #2 if desired. Either way, steel foundation tubes must be used at posts #1 and #2 for the wood post option.
NO!! The SKT requires eight special 1/2" high-strength cable anchor bracket shoulder bolts with two structural washers and a 1/2" structural nut on the traffic side. The unthreaded shoulders of the bolts provide the release mechanism for the anchor bracket for end-on impacts.
Yes, but there are certain conditions that must exist. The adjoining downstream 25'-0" length of the system must utilize standard W6" x 8.5# (or 9#) x 6'-0" long guardrail posts. In addition, if the SKT-SP is joining with anything other than standard W-Beam rail (i.e. Thrie Beam or a transition), an additional 12'-6" of standard W6" x 8.5# (or 9#) x 6'-0" long guardrail posts must be used.
FLEAT Wood and Steel Post System – Flared W-Beam Terminal
- Does the FLEAT terminal need to have additional flare if the run of guardrail it attaches to is already flared?
- Is a special attachment required to connect the last FLEAT rail section to the beginning of the run of guardrail where the straight flare begins?
- Can steel foundation tubes be used at FLEAT posts #3 through #7?
- Can standard hex bolts be used to attach the cable anchor bracket to the FLEAT guardrail end section?
- The FLEAT-SP (Standard Post) system is sometimes called out as 12'-6" long. Is that allowable?
When the FLEAT is attached to a run of guardrail that is parallel to the travelway, the offset flare for the FLEAT is measured from the point where the guardrail ends and the FLEAT begins. The offset for the Test Level 3 FLEAT can be varied anywhere between 2'-6" to 4'-0" (3.8 degrees to 6.1 degrees) over the 37'-6" long terminal length. The Test Level 2 FLEAT can be varied anywhere between 1'-8" to 2'-8" (3.8 degrees to 6.1 degrees) over the 25'-0" long terminal length. These offsets represent flare rates of 15:1 to approximately 10:1. When the FLEAT is attached to guardrail that has been flared per the recommendations of the AASHTO Roadside Design Guide, the flare rate for the FLEAT may not need to be changed from that of the downstream guardrail. If the flare rate of the guardrail falls between 15:1 and 10:1, install the FLEAT in line with the run of guardrail at the same flare rate. If the flare rate of the guardrail is less the 15:1, then you must adjust the FLEAT farther away from the run of guardrail to provide the proper flare rate. If the recommendations of the AASHTO Roadside Design Guide are followed, the standard run of guardrail will not have a flare rate that is greater than 10:1 (semi-rigid barriers) for Test Level 2 (70 km/hr) or Test Level 3 (100 km/hr) design speeds. This means the FLEAT should not need to be flared back toward the travelway with respect to the flare rate of the guardrail.
No. The contractor must install the FLEAT beginning at the downstream end where the run of guardrail begins and work toward post #1. The splice of the last FLEAT rail section where the flare departure begins (FLEAT post #7 for the 37'-6" long Test Level 3 system) must be firmly bolted before the rail within the FLEAT itself is flared. If desired, post #7 can be set back a short distance to minimize the severity of the bend at that post. The angle of departure will depend on the offset selected. Based on a Test Level 3 FLEAT that is 37'-6" long, the maximum angle will be 6.1 degrees for a 4'-0" offset and the minimum angle will be 3.8 degrees for a 2'-6" offset. For a Test Level 2 FLEAT, the angle will remain the same but the offset will change to 2'-8" and 1'-8" respectively.
No. The FLEAT only has steel foundation tubes at post #1 and #2. The tubes may either be the 6'-0" long steel foundation tubes without soil plates or the 4'-6" long foundation tubes with soil plates. Either way, steel foundation tubes must be used at posts #1 and #2 for the wood post option.
NO!! The FLEAT requires eight special 1/2" high-strength cable anchor bracket shoulder bolts with two structural washers and a 1/2" structural nut on the traffic side. The unthreaded shoulders of the bolts provide the release mechanism for the anchor bracket for end-on impacts.
Yes, but the adjoining downstream 25'-0" length of the system must utilize standard W6" x 8.5# (or 9#) x 6'-0" long guardrail posts.
SKT-MGS and FLEAT-MGS W-Beam Terminals for 31"-Tall Rail
- Can the SKT-MGS and FLEAT-MGS systems with 12" blockouts be used with the 31" tall Gregory Mini Spacer (GMS) system that does not use blockouts?
- Can standard hex bolts be used to attach the cable anchor bracket to the SKT-MGS or FLEAT-MGS guardrail end sections?
- Can 8" blocks be used in place of the 12" blocks for the SKT MGS or FLEAT MGS terminals?
Yes, but the offset caused by the blockouts in the terminal must be considered when driving the posts.
NO!! The SKT-MGS and FLEAT-MGS require eight special 1/2" high- strength cable anchor bracket shoulder bolts with two structural washers and a 1/2" structural nut on the traffic side. The unthreaded shoulders of the bolts provide the release mechanism for the anchor bracket for end-on impacts.
Yes, if the specifying agency has called for 8" blocks on the downstream MGS W-Beam Barrier, 8" blocks may be used in the terminals. Drawings are available upon request.
FLEAT-MT Wood or Steel Post – Median W-Beam Terminal
- Can the FLEAT-MT be used in either 1-way or 2-way traffic?
- Can the FLEAT-MT be installed using seven foundation tubes rather than the three tubes (at posts 1, 2 and 4) shown on the drawings?
- Can standard hex bolts be used to attach the cable anchor bracket to the FLEAT-MT guardrail end section?
Yes, but consideration should be given to placement of the front 18'-9" single-sided segment. That portion of the terminal should be placed on the side where traffic volumes would be expected to be heaviest.
Yes. Drawings are available for this option.
NO!! The FLEAT-MT requires eight special 1/2" high-strength cable anchor bracket shoulder bolts with two structural washers and a 1/2" structural nut on the traffic side. The unthreaded shoulders of the bolts provide the release mechanism for the anchor bracket for end-on impacts.
BEAT and BEAT-MT Box Beam Terminals
- The drawings show the BEAT to be 14 feet long. Is that allowable?
- The BEAT-MT (median terminal) uses many of the same parts as the BEAT (roadside terminal) including 6" x 6" box beam tube. Since box beam median barrier is 6" x 8", how is the BEAT-MT connected to 6" x 8" tubing?
Yes, but there are certain conditions that must exist. The adjoining downstream 18'-0" length of the system must utilize standard 6" x 6" box beam with standard 3" posts spaced at 6'-0".
There is a transition element that goes from 6" x 6" to 6" x 8" that is supplied with all BEAT-MT terminals.
BEAT-SSCC Single-Sided Crash Cushion
- Are there options available for varying lengths in the BEAT-SSCC?
- Are the breakaway posts for the BEAT-SSCC used anywhere else?
- Do the holes for the end wall anchor bolts need to be drilled all the way through the wall?
- Is a concrete foundation or pad required for the BEAT-SSCC?
Yes. Normally the standard TL-3 system is 28 feet long. In locations where additional Length-of-Need is required, the BEAT-SSCC is also available in lengths of 32 feet, 36 feet, 40 feet and 44 feet.
Yes. The plug-welded line posts are used in the BEAT-BP Bridge Pier system and may also be used in the SKT, FLEAT and FLEAT-MT W-Beam terminals. The front anchor post is used in the BEAT, BEAT-MT and the BEAT-SSCC box beam systems.
It depends. The bolt length and anchor requirements depend on the wall thickness. Anchorage systems that develop the full capacity of the bolt may be used as an alternate to drilling through the concrete wall.
No, the BEAT-SSCC is normally ground-mounted with driven posts. But a Surface-Mounted option is available if a concrete surface already exists.
BEAT-BP Bridge Pier System
- Can the BEAT-BP be used at varying locations where the number of piers, the size/shape of the piers and/or the spacing/positioning of the piers vary?
Yes. The BEAT-BP uses a common set of parts that will allow coverage of any length and width of pier structure. It's the same parts, but the quantities and the installation positioning will vary to shield the pier. The posts along the piers require at least 4-ft of cover to be installed. If the pier foundations cause interference, the layout can be adjusted to accommodate the site conditions.
TRANSITION Cable to W-Beam
- Is the Cable to W-Beam Transition recommended for the newer high- tension cable barrier systems?
No. The Cable to W-Beam Transition is recommended for low-tension cable barriers. The connections were not designed for the tension required in the high-tension systems. There are specific W-Beam transition designs for the high-tension cable barrier systems.
General Terminal Questions
- What are the recommended grading details adjacent to guardrail terminals?
- Can a terminal be used at a steep slope?
- When a terminal is installed on a steep grade, what is the proper placement of the impact head?
- Can terminals be used on a curve?
- Can breakaway steel posts be mixed with breakaway wood posts in the same SKT or FLEAT terminal?
- Can the SKT or FLEAT be supplied in weathering steel such as Corten?
- Can the BEAT Box Beam Systems be supplied in weathering steel such as Corten?
Special grading is required around guardrail terminals to assure that field performance is similar to that observed during full-scale crash testing. Relative to the placement of the terminal, FHWA refers to this as Advance Grading, Adjacent Grading and Run-out Grading. Note that crash testing is normally conducted on flat and level ground and it is important to avoid installing terminals on or too near steep slopes. Relatively flat terrain is required in front of guardrail terminals in order to assure that vehicles are not vaulted into the air or diving into the ground when the terminal is struck. Further, modest slopes are utilized behind guardrail terminals in order to allow sufficient recovery areas for vehicles gating through the end treatment. The FHWA has developed guideline requirements based on engineering judgment for both tangent and flared terminals. See FHWA Memo titled "Supplemental Guidance for the Selection of W-Beam Barrier Terminals" dated November 17, 2005 and the accompanying FHWA-issued CD ROM dated December 2006 for additional information. Generally, energy-absorbing terminals (such as the SKT and FLEAT) would require less stringent grading requirements than pure controlled gating terminals. Also see the recommended grading details shown in the AASHTO Roadside Design Guide. Ongoing additional research is needed to give better guidelines.
Remember that a terminal does not solve a slope problem. If there is a steep slope in the immediate vicinity of the terminal, additional barrier may be needed before the terminal is installed. See the question above on grading for additional information.
The important thing to remember is to keep the impact head parallel to the guardrail, not perpendicular to post #1. The reason is to allow the head to freely travel down the rail. The SKT and FLEAT impact heads are connected to the first post of the terminal with either two lag screws (for a wood post) or two hex head bolts (for a steel post). When the system is impacted end-on, the impact head only needs to move a short distance before the first post is fractured. The connection of the impact head to the post needs to be strong enough to support the weight of the head prior to impact. If the terminal is placed on a hill and the posts are driven so they will not be perpendicular to the guardrail, the post bracket angle on the impact head will not set flush against the post. Normally that gap will not exceed a width that will prevent the lag screw or hex bolt from holding the impact head to the post. If under extreme circumstances the gap becomes too large and the connection is not secure, we would recommend using a spacer and a longer bolt.
The SKT, FLEAT or BEAT terminals themselves cannot be curved. In order for the impact heads to travel down the rail during end-on impacts, the rail must be straight to maintain the column strength of the rail section. The last downstream rail section of the terminal may be bolted to the beginning of the first curved guardrail section but no curved sections are permitted within the terminal itself.
Yes, but this is not normally recommended -- with the exception of two steel posts at Locations 1 and 2, and wood CRT posts at Locations 3 and beyond. Also remember, it's important that the foundation tube criteria as described above is followed. With the exception of a few nuts and bolts and the wood blocks (routed blocks needed for the steel posts), all of the SKT and FLEAT components are interchangeable between the wood post and the steel post options.
The FHWA has recently taken the position that weathering steel should not be used in the W-Beam guardrail terminals because deterioration of the steel weakens the rail which could cause the rail to fail during impacts. Where aesthetics are the primary concern, we believe the best option to be galvanizing the impact head, the upper post #1 in our SP system and all guardrails in the W-Beam terminal before a brown powder coating finish is applied. In addition, if weathering steel posts are used, the lower portion that will be below ground must be hot dipped galvanized.
No. The materials must be hot-dipped galvanized. The galvanized surface on the inside of the tubing assists in allowing the impact head to burst the tube. The tube may be painted brown over the galvanized surface if desired.
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