Appendix to Subpart B of Part 646 - Horizontal and Vertical Clearance Provisions for Overpass and Underpass Structures
23:1.0.1.7.29.2.1.12.24 :
Appendix to Subpart B of Part 646 - Horizontal and Vertical
Clearance Provisions for Overpass and Underpass Structures
The following implements provisions of 23 CFR 646.212(a)(3).
a.
Lateral Geometrics
A cross section with a horizontal distance of 6.1 meters,
measured at right angles from the centerline of track at the top of
rails, to the face of the embankment slope, may be approved. The
6.1-meters distance may be increased at individual structure
locations as appropriate to provide for drainage if justified by a
hydraulic analysis or to allow adequate room to accommodate special
conditions, such as where heavy and drifting snow is a problem. The
railroad must demonstrate that this is its normal practice to
address these special conditions in the manner proposed.
Additionally, this distance may also be increased up to 2.5 meters
as may be necessary for off-track maintenance equipment, provided
adequate horizontal clearance is not available in adjacent spans
and where justified by the presence of an existing maintenance road
or by evidence of future need for such equipment. All piers should
be placed at least 2.8 meters horizontally from the centerline of
the track and preferably beyond the drainage ditch. For multiple
track facilities, all dimensions apply to the centerline of the
outside track.
Any increase above the 6.1-meters horizontal clearance distance
must be required by specific site conditions and be justified by
the railroad to the satisfaction of the State highway agency (SHA)
and the FHWA.
b.
Vertical Clearance
A vertical clearance of 7.1 meters above the top of rails, which
includes an allowance for future ballasting of the railroad tracks,
may be approved. Vertical clearance greater than 7.1 meters may be
approved when the State regulatory agency having jurisdiction over
such matters requires a vertical clearance in excess of 7.1 meters
or on a site by site basis where justified by the railroad to the
satisfaction of the SHA and the FHWA. A railroad's justification
for increased vertical clearance should be based on an analysis of
engineering, operational and/or economic conditions at a specific
structure location.
Federal-aid highway funds are also eligible to participate in
the cost of providing vertical clearance greater than 7.1 meters
where a railroad establishes to the satisfaction of a SHA and the
FHWA that it has a definite formal plan for electrification of its
rail system where the proposed grade separation project is located.
The plan must cover a logical independent segment of the rail
system and be approved by the railroad's corporate headquarters.
For 25 kv line, a vertical clearance of 7.4 meters may be approved.
For 50 kv line, a vertical clearance of 8.0 meters may be
approved.
A railroad's justification to support its plan for
electrification shall include maps and plans or drawings showing
those lines to be electrified; actions taken by its corporate
headquarters committing it to electrification including a proposed
schedule; and actions initiated or completed to date implementing
its electrification plan such as a showing of the amounts of funds
and identification of structures, if any, where the railroad has
expended its own funds to provide added clearance for the proposed
electrification. If available, the railroad's justification should
include information on its contemplated treatment of existing grade
separations along the section of its rail system proposed for
electrification.
The cost of reconstructing or modifying any existing
railroad-highway grade separation structures solely to accommodate
electrification will not be eligible for Federal-aid highway fund
participation.
c.
Railroad Structure Width
Two and eight tenths meters of structure width outside of the
centerline of the outside tracks may be approved for a structure
carrying railroad tracks. Greater structure width may be approved
when in accordance with standards established and used by the
affected railroad in its normal practice.
In order to maintain continuity of off-track equipment roadways
at structures carrying tracks over limited access highways,
consideration should be given at the preliminary design stage to
the feasibility of using public road crossings for this purpose.
Where not feasible, an additional structure width of 2.5 meters may
be approved if designed for off-track equipment only.
[53 FR 32218, Aug. 24, 1988, as amended at 62 FR 45328, Aug. 27,
1997]