Chapter 8A. General
Section 8A.01 Introduction
Traffic control for highway-rail grade crossings includes all signs,
signals, markings, other warning devices, and their supports along
highways approaching and at highway-rail grade crossings. The function
of this traffic control is to permit reasonably safe and efficient
operation of both rail and highway traffic at highway-rail grade
For purposes of installation, operation, and maintenance
of traffic control devices at highway-rail grade crossings, it is
recognized that the crossing of the highway and rail tracks is situated
on a right-of-way available for the joint use of both highway traffic
and railroad traffic.
The highway agency or authority with jurisdiction
and the regulatory agency with statutory authority, if applicable,
jointly determine the need and selection of devices at a highway-rail
In Part 8, the combination of devices selected
or installed at a specific highway-rail grade crossing is referred
to as a "traffic control system."
The traffic control devices, systems, and practices described herein
shall be used at all highway-rail grade crossings open to public
travel, consistent with Federal, State, and local laws and regulations.
To promote an understanding of common terminology
between highway and railroad signaling issues, the following definitions
shall be used:
- Advance Preemption—the notification of an approaching
train that is forwarded to the highway traffic signal controller
unit or assembly by the railroad equipment in advance of the
activation of the railroad warning devices.
- Advance Preemption Time—the period of time that is the
difference between the required maximum highway traffic signal
preemption time and the activation of the railroad warning devices.
- Cantilevered Signal Structure—a structure that is rigidly
attached to a vertical pole and is used to provide overhead
support of signal units.
- Clear Storage Distance—the distance available for vehicle
storage measured between 1.8 m (6 ft) from the rail nearest
the intersection to the intersection stop line or the normal
stopping point on the highway. At skewed highway-rail grade
crossings and intersections, the 1.8 m (6 ft) distance shall
be measured perpendicular to the nearest rail either along the
centerline or edge line of the highway, as appropriate, to obtain
the shorter distance. Where exit gates are used, the distance
available for vehicle storage is measured from the point where
the rear of the vehicle would be clear of the exit gate arm.
In cases where the exit gate arm is parallel to the track(s)
and is not perpendicular to the highway, the distance is measured
either along the centerline or edge line of the highway, as
appropriate, to obtain the shorter distance.
- Design Vehicle—the longest vehicle permitted by statute
of the road authority (State or other) on that roadway.
- Dynamic Envelope—the clearance required for the train
and its cargo overhang due to any combination of loading, lateral
motion, or suspension failure (see Figure 8A-1).
8A-1 Train Dynamic Envelope
- Dynamic Exit Gate Operating Mode—a mode of operation
where the exit gate operation is based on the presence of vehicles
within the minimum track clearance distance.
- Exit Gate Clearance Time—for Four-Quadrant Gate systems,
the exit gate clearance time is the amount of time provided
to delay the descent of the exit gate arm(s) after the entrance
gate arm(s) begin to descend.
- Exit Gate Operating Mode—for Four-Quadrant Gate systems,
the mode of control used to govern the operation of the exit
- Flashing-Light Signals—a warning device consisting of
two red signal indications arranged horizontally that are activated
to flash alternately when a train is approaching or present
at a highway-rail grade crossing.
- Interconnection—the electrical connection between the
railroad active warning system and the highway traffic signal
controller assembly for the purpose of preemption.
- Maximum Highway Traffic Signal Preemption Time—the maximum
amount of time needed following initiation of the preemption
sequence for the highway traffic signals to complete the timing
of the right-of-way transfer time, queue clearance time, and
- Minimum Track Clearance Distance—for standard two-quadrant
railroad warning devices, the minimum track clearance distance
is the length along a highway at one or more railroad tracks,
measured either from the highway stop line, warning device,
or 3.7 m (12 ft) perpendicular to the track centerline, to 1.8
m (6 ft) beyond the track(s) measured perpendicular to the far
rail, along the centerline or edge line of the highway, as appropriate,
to obtain the longer distance. For Four-Quadrant Gate systems,
the minimum track clearance distance is the length along a highway
at one or more railroad tracks, measured either from the highway
stop line or entrance warning device, to the point where the
rear of the vehicle would be clear of the exit gate arm. In
cases where the exit gate arm is parallel to the track(s) and
is not perpendicular to the highway, the distance is measured
either along the centerline or edge of the highway, as appropriate,
to obtain the longer distance.
- Minimum Warning Time—Through Train Movements—the
least amount of time active warning devices shall operate prior
to the arrival of a train at a highway-rail grade crossing.
- Preemption—the transfer of normal operation of highway
traffic signals to a special control mode.
- Pre-signal—supplemental highway traffic signal faces
operated as part of the highway intersection traffic signals,
located in a position that controls traffic approaching the
highway-rail grade crossing in advance of the intersection.
- Queue Clearance Time—the time required for the design
vehicle of maximum length stopped just inside the minimum track
clearance distance to start up and move through and clear the
entire minimum track clearance distance. If presignals are present,
this time shall be long enough to allow the vehicle to move
through the intersection, or to clear the tracks if there is
sufficient clear storage distance. If a Four-Quadrant Gate system
is present, this time shall be long enough to permit the exit
gate arm to lower after the design vehicle is clear of the minimum
track clearance distance.
- Right-of-Way Transfer Time—the maximum amount of time
needed for the worst case condition, prior to display of the
track clearance green interval. This includes any railroad or
highway traffic signal control equipment time to react to a
preemption call, and any traffic control signal green, pedestrian
walk and clearance, yellow change, and red clearance intervals
for conflicting traffic.
- Separation Time—the component of maximum highway traffic
signal preemption time during which the minimum track clearance
distance is clear of vehicular traffic prior to the arrival
of the train.
- Simultaneous Preemption—notification of an approaching
train is forwarded to the highway traffic signal controller
unit or assembly and railroad active warning devices at the
- Timed Exit Gate Operating Mode—a mode of operation where
the exit gate descent is based on a predetermined time interval.
- Vehicle Intrusion Detection Devices—a detector or detectors
used as a part of a system incorporating processing logic to
detect the presence of vehicles within the minimum track clearance
distance and to control the operation of the exit gates.
- Wayside Equipment—the signals, switches, and/or control
devices for railroad operations housed within one or more enclosures
located along the railroad right-of-way and/or on railroad
Section 8A.02 Use
of Standard Devices, Systems, and Practices
Because of the large number of significant variables to be considered,
no single standard system of traffic control devices is universally
applicable for all highway-rail grade crossings.
The appropriate traffic control system to be used at a highway-rail
grade crossing should be determined by an engineering study involving
both the highway agency and the railroad company.
The engineering study may include the Highway-Rail Intersection
(HRI) components of the National Intelligent Transportation Systems
(ITS) architecture, which is a USDOT accepted method for linking
the highway, vehicles, and traffic management systems with rail
operations and wayside equipment.
More detail on Highway-Rail Intersection components is available
from USDOT’s Federal Railroad Administration, 1120 Vermont
Ave., NW, Washington, DC 20590, or www.fra.dot.gov.
Traffic control devices, systems, and practices shall be consistent
with the design and application of the Standards contained herein.
Before any new highway-rail grade crossing traffic
control system is installed or before modifications are made to
an existing system, approval shall be obtained from the highway
agency with the jurisdictional and/or statutory authority, and from
the railroad company.
To stimulate effective responses from vehicle operators and pedestrians,
these devices, systems, and practices should use the five basic
considerations employed generally for traffic control devices and
described fully in Section
1A.02: design, placement, operation, maintenance, and uniformity.
Many other details of highway-rail grade crossing traffic control
systems that are not set forth in Part 8 are contained in the publications
listed in Section 1A.11.
Section 8A.03 Uniform
All signs used in highway-rail grade crossing traffic control systems
shall be retroreflectorized or illuminated as described in Section
2A.08 to show the same shape and similar color to an approaching
road user during both day and night.
No sign or signal shall be located in the center
of an undivided highway, except in a raised island.
Such signs or signals should be installed with a clearance of at
least 0.6 m (2 ft) from the outer edge of the raised island to the
nearest edge of the sign or signal, except as allowed in Section
Where the distance between tracks, measured along
the highway between the inside rails, exceeds 30 m (100 ft), additional
signs or other appropriate traffic control devices should be used.
Section 8A.04 Highway-Rail
Grade Crossing Elimination
Because highway-rail grade crossings are a potential source of crashes
and congestion, agencies should conduct engineering studies to determine
the cost and benefits of eliminating these crossings.
When a highway-rail grade crossing is eliminated, the traffic control
devices for the crossing shall be removed.
If the existing traffic control devices
at a multiple-track highway-rail grade crossing become improperly
placed or inaccurate because of the removal of some of the tracks,
the existing devices shall be relocated and/or modified.
Any highway-rail grade crossing that cannot be justified should
Where a roadway is removed from a highway-rail
grade crossing, the roadway approaches in the railroad right-of-way
should also be removed and appropriate signs should be placed at
the roadway end in accordance with Section
Where a railroad is eliminated at a highway-rail
grade crossing, the tracks should be removed or paved over.
Based on engineering judgment, the TRACKS OUT OF SERVICE (R8-9)
sign (see Figure 8B-3) may be
temporarily installed until the tracks are removed or paved over.
The length of time before the tracks will be removed or paved over
may be considered in making the decision as to whether to install
Section 8A.05 Temporary
Traffic Control Zones
Temporary traffic control planning provides for continuity of operations
(such as movement of traffic, pedestrians and bicycles, transit
operations, and access to property/utilities) when the normal function
of a roadway at a highway-rail grade crossing is suspended because
of temporary traffic control operations.
Traffic controls for temporary traffic control zones that include
highway-rail grade crossings shall be as outlined in Part
When a highway-rail grade crossing exists either
within or in the vicinity of a temporary traffic control zone, lane
restrictions, flagging, or other operations shall not be performed
in a manner that would cause vehicles to stop on the railroad tracks,
unless a law enforcement officer or flagger is provided at the highway-rail
grade crossing to minimize the possibility of vehicles stopping
on the tracks, even if automatic warning devices are in place.
Public and private agencies, including emergency services, businesses,
and railroad companies, should meet to plan appropriate traffic
detours and the necessary signing, marking, and flagging requirements
for operations during temporary traffic control zone activities.
Consideration should be given to the length of time that the highway-rail
grade crossing is to be closed, the type of rail and highway traffic
affected, the time of day, and the materials and techniques of repair.
Temporary traffic control operations should minimize
the inconvenience, delay, and crash potential to affected traffic.
Prior notice should be given to affected public or private agencies,
emergency services, businesses, railroad companies, and road users
before the free movement of vehicles or trains is infringed upon
Temporary traffic control zone activities should
not be permitted to extensively prolong the closing of the highway-rail
The width, grade, alignment, and riding quality
of the highway surface at a highway-rail grade crossing should,
at a minimum, be restored to correspond with the quality of the
approaches to the highway-rail grade crossing.
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