Guardrail frequently asked questions
End Treatments - Terminals
Yes. You will need to add a section of guardrail that transitions vertically between the existing 28" height guardrail and the new 31" end terminal. See Standard Plan 601.
For anchors near Bullnose Guardrail, recommended clearance is 20’. See Standard Plan 688.
For anchorages at median crossover, recommended clearance is 20’ from crossover.
For anchorages at signalized intersections coordinate with Maintenance and Traffic offices to determine the best location. These locations are unique and require context for determining optimal location.
For further information consult with Design Standards Unit.
Yes. You will need to add a section of guardrail that transitions vertically between the existing 28" height guardrail and the new 31" end terminal. See Standard Plan 601.
For anchors near Bullnose Guardrail, recommended clearance is 20’. See Standard Plan 688.
For anchorages at median crossover, recommended clearance is 20’ from crossover.
For anchorages at signalized intersections coordinate with Maintenance and Traffic offices to determine the best location. These locations are unique and require context for determining optimal location.
For further information consult with Design Standards Unit.
Guardrail
Working width is defined as the distance between the barrier face before impact and the maximum lateral position of any major part of the system or vehicle during or after impact. This area should be free of any hazards or fixed objects. This detail (PDF) shows how working width is measured.
Yes. Standard plan 695 shows an AGT design to connect a Type 31 guardrail to an F- or J-shape barrier.
If the design shown on standard plan 695 will not work for your project, standard plans 603, 605, 607, 609, 618, and 619 show alternate AGT designs, although the AGT height for these barriers is shorter. The Type 31 guardrail must transition vertically from 31” to 28” prior to connecting to these AGTs. This 3" vertical transition extends over 25' horizontal transition. See standard plan 601 for the vertical transition.
Contact Design Standards if your project has need for a connection without a transition.
This depends on how far (laterally) off of the pavement the guardrail is located, and whether there is curb. This detail (PDF) shows the proper way to measure height of guardrail for different situations.
The Type 31 guardrail (Standard Plan 690) has been successfully tested with up to three consecutive posts omitted, leaving a maximum span of 25 feet between posts. Three CRT wood posts are required at either end of the span. Rail nesting is not required. See Standard Plan 696.
For Type 31 guardrail in non-curbed sections, omitting a single guardrail post is allowed once every 50’ without additional measures taken.
For Type 31 guardrail in curbed sections, a single post may be omitted with the use of 37’6” of nested rail centered about the omitted post.
28" guardrail (Standard Plate 8338) can also have up to three consecutive posts omitted. Three CRT wood posts are required at either side of the span. The rail needs to be nested across the span as well as up- and down-stream from the gap, for a total length of 100 feet.
Note: Guardrail deflection distances/working widths increase when posts are omitted.
Short radius designs use 28”-tall guardrail based on Standard Plate 8307. If you have Type 31 guardrail along the main roadway approaching a short radius installation, use a 25’-long vertical height transition to reduce the guardrail height from 31” to 28” before reaching the short radius guardrail. See Standard Plan 697 for short radius design details and Standard Plan 601 for height transition details.
Guardrail posts must be placed in soil that has a surface slope of 1V:10H or flatter. That slope can break to a 1V:2H or flatter slope with the slope break no less than 24 inches behind the guardrail post. Type 31 guardrail has been tested and approved for installation adjacent to a 1V:2H slope with the slope break at the back of the post when using posts that are 9 feet long. See Standard Plan 690.
A straightforward method to field verify LON in the field is to stand on the roadway edge directly opposite the shielded feature, and then pace off the appropriate runout length from Exhibit 10C-7 in the Facility Design Guide. At that point, turn and look at the shielded area. If the guardrail installation overlaps that line by at least 20’, the area is adequately covered.
(If runout length values from the Table are unavailable pace off 300’ for high speed roadways or 200’ for low speed. If guardrail crosses this line of sight +/- 50’, the area is adequately covered.)
Note: This method is for field use only and should not be used when designing new or replacement systems. The gating section of the end terminal cannot be included in the length of need. Gating sections have different lengths for each proprietary system. For rough estimate ensure that 20ft is past the line of sight.
Refer to this detail (PDF).
For Type 31 Guardrail (Standard Plan 690) and guardrail that is 28” in height, two 8" blockouts (16” maximum) may be used at any time for any number of posts. Three 8" blockouts, or two 12" blockouts (24" maximum) may be used at one post only once per 75’.
For Type 31 guardrail, 8” blockouts may be used in place of 12” blockouts.
For Approach Guardrail Transitions (Standard Plans 608, 693, 694, and 695.), additional blockouts are not acceptable with 12” blockouts. Two 8” blockouts may be used in limited applications depending on site condition. Consult with Design Standards.
Post bolt slots on standard w-beam rail are normally spaced at 3’ 1-1/2” (half post spacing). If the rail has no post bolt slots at ¼ post spacing the post with bolted blockout attached can be set flush behind the rail without drilling the slot in the guardrail. Guard rail posts, blockouts, and post bolts through the rail are required at all full and half spaced rail locations.
Generally, a guardrail post can be set in a 1V:2H or flatter cut slope which allows for adequate post movement.
Guardrail can be installed adjacent to curb provided Standard Plan 690 is followed.
See the Facility Design Guide for guidance on preservation projects.
Working width is defined as the distance between the barrier face before impact and the maximum lateral position of any major part of the system or vehicle during or after impact. This area should be free of any hazards or fixed objects. This detail (PDF) shows how working width is measured.
Yes. Standard plan 695 shows an AGT design to connect a Type 31 guardrail to an F- or J-shape barrier.
If the design shown on standard plan 695 will not work for your project, standard plans 603, 605, 607, 609, 618, and 619 show alternate AGT designs, although the AGT height for these barriers is shorter. The Type 31 guardrail must transition vertically from 31” to 28” prior to connecting to these AGTs. This 3" vertical transition extends over 25' horizontal transition. See standard plan 601 for the vertical transition.
Contact Design Standards if your project has need for a connection without a transition.
This depends on how far (laterally) off of the pavement the guardrail is located, and whether there is curb. This detail (PDF) shows the proper way to measure height of guardrail for different situations.
The Type 31 guardrail (Standard Plan 690) has been successfully tested with up to three consecutive posts omitted, leaving a maximum span of 25 feet between posts. Three CRT wood posts are required at either end of the span. Rail nesting is not required. See Standard Plan 696.
For Type 31 guardrail in non-curbed sections, omitting a single guardrail post is allowed once every 50’ without additional measures taken.
For Type 31 guardrail in curbed sections, a single post may be omitted with the use of 37’6” of nested rail centered about the omitted post.
28" guardrail (Standard Plate 8338) can also have up to three consecutive posts omitted. Three CRT wood posts are required at either side of the span. The rail needs to be nested across the span as well as up- and down-stream from the gap, for a total length of 100 feet.
Note: Guardrail deflection distances/working widths increase when posts are omitted.
Short radius designs use 28”-tall guardrail based on Standard Plate 8307. If you have Type 31 guardrail along the main roadway approaching a short radius installation, use a 25’-long vertical height transition to reduce the guardrail height from 31” to 28” before reaching the short radius guardrail. See Standard Plan 697 for short radius design details and Standard Plan 601 for height transition details.
Guardrail posts must be placed in soil that has a surface slope of 1V:10H or flatter. That slope can break to a 1V:2H or flatter slope with the slope break no less than 24 inches behind the guardrail post. Type 31 guardrail has been tested and approved for installation adjacent to a 1V:2H slope with the slope break at the back of the post when using posts that are 9 feet long. See Standard Plan 690.
A straightforward method to field verify LON in the field is to stand on the roadway edge directly opposite the shielded feature, and then pace off the appropriate runout length from Exhibit 10C-7 in the Facility Design Guide. At that point, turn and look at the shielded area. If the guardrail installation overlaps that line by at least 20’, the area is adequately covered.
(If runout length values from the Table are unavailable pace off 300’ for high speed roadways or 200’ for low speed. If guardrail crosses this line of sight +/- 50’, the area is adequately covered.)
Note: This method is for field use only and should not be used when designing new or replacement systems. The gating section of the end terminal cannot be included in the length of need. Gating sections have different lengths for each proprietary system. For rough estimate ensure that 20ft is past the line of sight.
Refer to this detail (PDF).
For Type 31 Guardrail (Standard Plan 690) and guardrail that is 28” in height, two 8" blockouts (16” maximum) may be used at any time for any number of posts. Three 8" blockouts, or two 12" blockouts (24" maximum) may be used at one post only once per 75’.
For Type 31 guardrail, 8” blockouts may be used in place of 12” blockouts.
For Approach Guardrail Transitions (Standard Plans 608, 693, 694, and 695.), additional blockouts are not acceptable with 12” blockouts. Two 8” blockouts may be used in limited applications depending on site condition. Consult with Design Standards.
Post bolt slots on standard w-beam rail are normally spaced at 3’ 1-1/2” (half post spacing). If the rail has no post bolt slots at ¼ post spacing the post with bolted blockout attached can be set flush behind the rail without drilling the slot in the guardrail. Guard rail posts, blockouts, and post bolts through the rail are required at all full and half spaced rail locations.
Generally, a guardrail post can be set in a 1V:2H or flatter cut slope which allows for adequate post movement.
Guardrail can be installed adjacent to curb provided Standard Plan 690 is followed.
See the Facility Design Guide for guidance on preservation projects.
This depends on how far (laterally) off of the pavement the guardrail is located, and whether there is curb. This detail (PDF) shows the proper way to measure height of guardrail for different situations.
The Type 31 guardrail (Standard Plan 690) has been successfully tested with up to three consecutive posts omitted, leaving a maximum span of 25 feet between posts. Three CRT wood posts are required at either end of the span. Rail nesting is not required. See Standard Plan 696.
For Type 31 guardrail in non-curbed sections, omitting a single guardrail post is allowed once every 50’ without additional measures taken.
For Type 31 guardrail in curbed sections, a single post may be omitted with the use of 37’6” of nested rail centered about the omitted post.
28" guardrail (Standard Plate 8338) can also have up to three consecutive posts omitted. Three CRT wood posts are required at either side of the span. The rail needs to be nested across the span as well as up- and down-stream from the gap, for a total length of 100 feet.
Note: Guardrail deflection distances/working widths increase when posts are omitted.
Short radius designs use 28”-tall guardrail based on Standard Plate 8307. If you have Type 31 guardrail along the main roadway approaching a short radius installation, use a 25’-long vertical height transition to reduce the guardrail height from 31” to 28” before reaching the short radius guardrail. See Standard Plan 697 for short radius design details and Standard Plan 601 for height transition details.
Guardrail posts must be placed in soil that has a surface slope of 1V:10H or flatter. That slope can break to a 1V:2H or flatter slope with the slope break no less than 24 inches behind the guardrail post. Type 31 guardrail has been tested and approved for installation adjacent to a 1V:2H slope with the slope break at the back of the post when using posts that are 9 feet long. See Standard Plan 690.
A straightforward method to field verify LON in the field is to stand on the roadway edge directly opposite the shielded feature, and then pace off the appropriate runout length from Exhibit 10C-7 in the Facility Design Guide. At that point, turn and look at the shielded area. If the guardrail installation overlaps that line by at least 20’, the area is adequately covered.
(If runout length values from the Table are unavailable pace off 300’ for high speed roadways or 200’ for low speed. If guardrail crosses this line of sight +/- 50’, the area is adequately covered.)
Note: This method is for field use only and should not be used when designing new or replacement systems. The gating section of the end terminal cannot be included in the length of need. Gating sections have different lengths for each proprietary system. For rough estimate ensure that 20ft is past the line of sight.
Refer to this detail (PDF).
For Type 31 Guardrail (Standard Plan 690) and guardrail that is 28” in height, two 8" blockouts (16” maximum) may be used at any time for any number of posts. Three 8" blockouts, or two 12" blockouts (24" maximum) may be used at one post only once per 75’.
For Type 31 guardrail, 8” blockouts may be used in place of 12” blockouts.
For Approach Guardrail Transitions (Standard Plans 608, 693, 694, and 695.), additional blockouts are not acceptable with 12” blockouts. Two 8” blockouts may be used in limited applications depending on site condition. Consult with Design Standards.
Post bolt slots on standard w-beam rail are normally spaced at 3’ 1-1/2” (half post spacing). If the rail has no post bolt slots at ¼ post spacing the post with bolted blockout attached can be set flush behind the rail without drilling the slot in the guardrail. Guard rail posts, blockouts, and post bolts through the rail are required at all full and half spaced rail locations.
Generally, a guardrail post can be set in a 1V:2H or flatter cut slope which allows for adequate post movement.
Guardrail can be installed adjacent to curb provided Standard Plan 690 is followed.
See the Facility Design Guide for guidance on preservation projects.
Short radius designs use 28”-tall guardrail based on Standard Plate 8307. If you have Type 31 guardrail along the main roadway approaching a short radius installation, use a 25’-long vertical height transition to reduce the guardrail height from 31” to 28” before reaching the short radius guardrail. See Standard Plan 697 for short radius design details and Standard Plan 601 for height transition details.
Guardrail posts must be placed in soil that has a surface slope of 1V:10H or flatter. That slope can break to a 1V:2H or flatter slope with the slope break no less than 24 inches behind the guardrail post. Type 31 guardrail has been tested and approved for installation adjacent to a 1V:2H slope with the slope break at the back of the post when using posts that are 9 feet long. See Standard Plan 690.
A straightforward method to field verify LON in the field is to stand on the roadway edge directly opposite the shielded feature, and then pace off the appropriate runout length from Exhibit 10C-7 in the Facility Design Guide. At that point, turn and look at the shielded area. If the guardrail installation overlaps that line by at least 20’, the area is adequately covered.
(If runout length values from the Table are unavailable pace off 300’ for high speed roadways or 200’ for low speed. If guardrail crosses this line of sight +/- 50’, the area is adequately covered.)
Note: This method is for field use only and should not be used when designing new or replacement systems. The gating section of the end terminal cannot be included in the length of need. Gating sections have different lengths for each proprietary system. For rough estimate ensure that 20ft is past the line of sight.
Refer to this detail (PDF).
For Type 31 Guardrail (Standard Plan 690) and guardrail that is 28” in height, two 8" blockouts (16” maximum) may be used at any time for any number of posts. Three 8" blockouts, or two 12" blockouts (24" maximum) may be used at one post only once per 75’.
For Type 31 guardrail, 8” blockouts may be used in place of 12” blockouts.
For Approach Guardrail Transitions (Standard Plans 608, 693, 694, and 695.), additional blockouts are not acceptable with 12” blockouts. Two 8” blockouts may be used in limited applications depending on site condition. Consult with Design Standards.
Post bolt slots on standard w-beam rail are normally spaced at 3’ 1-1/2” (half post spacing). If the rail has no post bolt slots at ¼ post spacing the post with bolted blockout attached can be set flush behind the rail without drilling the slot in the guardrail. Guard rail posts, blockouts, and post bolts through the rail are required at all full and half spaced rail locations.
Generally, a guardrail post can be set in a 1V:2H or flatter cut slope which allows for adequate post movement.
Guardrail can be installed adjacent to curb provided Standard Plan 690 is followed.
See the Facility Design Guide for guidance on preservation projects.
A straightforward method to field verify LON in the field is to stand on the roadway edge directly opposite the shielded feature, and then pace off the appropriate runout length from Exhibit 10C-7 in the Facility Design Guide. At that point, turn and look at the shielded area. If the guardrail installation overlaps that line by at least 20’, the area is adequately covered.
(If runout length values from the Table are unavailable pace off 300’ for high speed roadways or 200’ for low speed. If guardrail crosses this line of sight +/- 50’, the area is adequately covered.)
Note: This method is for field use only and should not be used when designing new or replacement systems. The gating section of the end terminal cannot be included in the length of need. Gating sections have different lengths for each proprietary system. For rough estimate ensure that 20ft is past the line of sight.
Refer to this detail (PDF).
For Type 31 Guardrail (Standard Plan 690) and guardrail that is 28” in height, two 8" blockouts (16” maximum) may be used at any time for any number of posts. Three 8" blockouts, or two 12" blockouts (24" maximum) may be used at one post only once per 75’.
For Type 31 guardrail, 8” blockouts may be used in place of 12” blockouts.
For Approach Guardrail Transitions (Standard Plans 608, 693, 694, and 695.), additional blockouts are not acceptable with 12” blockouts. Two 8” blockouts may be used in limited applications depending on site condition. Consult with Design Standards.
Post bolt slots on standard w-beam rail are normally spaced at 3’ 1-1/2” (half post spacing). If the rail has no post bolt slots at ¼ post spacing the post with bolted blockout attached can be set flush behind the rail without drilling the slot in the guardrail. Guard rail posts, blockouts, and post bolts through the rail are required at all full and half spaced rail locations.
Generally, a guardrail post can be set in a 1V:2H or flatter cut slope which allows for adequate post movement.
Guardrail can be installed adjacent to curb provided Standard Plan 690 is followed.
See the Facility Design Guide for guidance on preservation projects.
Post bolt slots on standard w-beam rail are normally spaced at 3’ 1-1/2” (half post spacing). If the rail has no post bolt slots at ¼ post spacing the post with bolted blockout attached can be set flush behind the rail without drilling the slot in the guardrail. Guard rail posts, blockouts, and post bolts through the rail are required at all full and half spaced rail locations.
Generally, a guardrail post can be set in a 1V:2H or flatter cut slope which allows for adequate post movement.
Guardrail can be installed adjacent to curb provided Standard Plan 690 is followed.
See the Facility Design Guide for guidance on preservation projects.
Guardrail can be installed adjacent to curb provided Standard Plan 690 is followed.
See the Facility Design Guide for guidance on preservation projects.
Transitions
The Approach Guardrail Transition (AGT) is a newer term for what has been historically called a Design Special by MnDOT. This new terminology better represents the system's purpose and also brings MnDOT in line with other States.
No, Standard Plate 8318 is not used with Type 31 AGT. Type 31 AGT shall be used on the approach end and the departing/trailing end of bridge rail/barrier if guardrail is needed
For single slope barrier (Standard Plan 681) and/or single slope bridge end post connection use Standard Plan 5-297.694.
For vertical bridge end post connection use Standard Plan 5-297.693.
For F-Shape and J-Shape bridge rail connections use Standard Plan 5-297.695.
Type 31 AGT shall be used on the departing/trailing end of bridge rail/barrier if guardrail is needed. See Standard Plans 693, 694, and 695.
The Approach Guardrail Transition (AGT) is a newer term for what has been historically called a Design Special by MnDOT. This new terminology better represents the system's purpose and also brings MnDOT in line with other States.
No, Standard Plate 8318 is not used with Type 31 AGT. Type 31 AGT shall be used on the approach end and the departing/trailing end of bridge rail/barrier if guardrail is needed
For single slope barrier (Standard Plan 681) and/or single slope bridge end post connection use Standard Plan 5-297.694.
For vertical bridge end post connection use Standard Plan 5-297.693.
For F-Shape and J-Shape bridge rail connections use Standard Plan 5-297.695.
Type 31 AGT shall be used on the departing/trailing end of bridge rail/barrier if guardrail is needed. See Standard Plans 693, 694, and 695.
For single slope barrier (Standard Plan 681) and/or single slope bridge end post connection use Standard Plan 5-297.694.
For vertical bridge end post connection use Standard Plan 5-297.693.
For F-Shape and J-Shape bridge rail connections use Standard Plan 5-297.695.
Type 31 AGT shall be used on the departing/trailing end of bridge rail/barrier if guardrail is needed. See Standard Plans 693, 694, and 695.