Section 4: Placement of Guard FenceAnchor: #i1005411
The placement of guard fence pertains to the lateral and longitudinal position.Anchor: #i1005422
Lateral Placement at Shoulder Edge or Curb Face
Typically the face of rail is placed at the shoulder edge or curb face throughout most of its length as shown in Figure A-4.
Figure A-4. Placement at Shoulder Edge or Curb Face
Guard fence placed in the vicinity of curbs should be blocked out so that the face of curb is located directly below or behind the face of rail. Rail placed over curbs should be installed so that the post bolt is located 25 in [550 mm] above the gutter pan or roadway surface.Anchor: #i1005448
Lateral Placement Away From the Shoulder Edge
In certain instances it is desirable to place guard fence closer to the obstacle rather than at the shoulder edge or curb face as shown in Figure A-5. Placement in this manner can substantially reduce the length of rail required to shield a given obstacle and minimize the probability of impact, but undesirably, encroachment angles may increase. This manner of placement is most applicable to small areas of concern—point type obstacles such as overhead sign bridge supports, bridge piers, etc.
To preclude vaulting or impacting at an undesirable position by errant vehicles; care should be exercised in selecting placement location of guard fence with respect to slope conditions. Guard fence may be placed at any lateral location on a side slope only if the slope rate between the edge of the pavement and the face of the barrier is 1V:10H or flatter.
Figure A-5. Location of Roadside Guard fence. Click here to see a PDF of the image.