13.11 Railroad-Highway Grade Crossings
13.11.1 Horizontal Alignment
If practical, the roadway should intersect the tracks at a right angle with no nearby intersections or driveways. This layout enhances the driver's view of the crossing and tracks, reduces conflicting vehicular movements from crossroads and driveways, and is preferred for bicyclists and pedestrians.
Highly skewed railroad-highway crossings can cause wheels of bicycles to get caught in the gap between the rail and pavement. To the extent practical, crossings should not be located on either roadway or railroad curves. Roadway curvature inhibits a driver's view of crossing ahead. A driver's attention may be directed toward negotiating the curve rather than looking for a train. Railroad curvature may inhibit a driver's view down the tracks from both a stopped position at the crossing and on the approach to the crossing. Those crossings that are located on both roadway and railroad curves present maintenance challenges and poor rideability for roadway traffic due to conflicting superelevation.
Where roadways that are parallel with main tracks intersect roadways that cross the main tracks, there should be sufficient distance between the tracks and the roadway intersections to enable roadway traffic in all directions to move expeditiously. Where physically restricted areas make it impractical to obtain adequate storage distance between the main track and a roadway intersection, the following should be considered:
- Interconnection of the roadway traffic signals with the grade crossing signals to enable vehicles to clear the grade crossing when a train approaches; and
- Placement of a "Do Not Stop on Tracks" sign on the roadway approach to the grade crossing
13.11.2 Vertical Alignment
It is desirable from the standpoint of sight distance, rideability, braking, and acceleration distances that the intersection of roadway and railroad be made as level as practical. Vertical curves should be of sufficient length to provide an adequate view of the crossing.
In some instances, the roadway vertical alignment may not meet acceptable geometrics for a given design speed because of restrictive topography or limitations of ROW. To prevent drivers of low-clearance vehicles from becoming caught on the tracks,
the road crossing surface should be level with the top of the rail for a distance of 2-ft from the nearest rail and not more than 3 inches higher or lower than the top of the nearest rail at a point 30-ft from the rail,
as shown in
. Vertical curves should be used to traverse from the roadway grade to a level plane at the elevation of the rails. Rails that are superelevated, or a roadway approach section that is not level, need a site-specific analysis for rail clearances.
Figure 13-18: Railroad-Highway Grade Crossing
Source: AASHTO A Policy on Geometric Design of Highways and Streets
13.11.3 Crossing Design
The geometric design of railroad-highway grade crossings should be made jointly when determining the warning devices to be used. When only passive warning devices are used, such as signs and pavement markings, the roadway drivers are warned of the crossing location but need to determine for themselves whether there are train movements for which they should stop. On the other hand, when active warning devices such as flashing light signals or automatic gates are used, the driver is given a positive indication of the presence or the approach of a train at the crossing. Many significant variables should be considered in determining the type of warning device to be installed at a railroad-grade crossing. For certain low-volume roadway crossings, where adequate sight distance is not available, additional signing may be needed.
Traffic control devices for railroad-highway grade crossings consist primarily of signs, pavement markings, flashing light signals, and automatic gates. Criteria for the design, placement, installment, and operation of these devices, refer to the
, as well as the use of various passive warning devices.
Some of the considerations for evaluating the need for active warning devices at a grade crossing include the type of roadway, volume of vehicular traffic, volume of railroad traffic, maximum speed of the railroad trains, permissible speed of vehicular traffic, volume of pedestrian traffic, crash history, sight distance, and geometrics of the crossing. The potential for complete elimination of grade crossings without active traffic control devices (e.g., closing lightly used crossings and installing active devices at other more heavily used crossings) should be given prime consideration.
These guidelines are not all-inclusive. Situations not covered by these guidelines should be evaluated using good engineering judgment. Additional information on railroad-highway grade crossings can be found in the following sources:
- Railroad-Highway Grade Crossing Handbook;
- Railroad-Highway Grade Crossing Surfaces;
- Sight Distance and Approach Speed;
- Traffic Control and Roadway Elements-their Relationship to Highway Safety;
- NCHRP Report 288; and
- Traffic Control Devices and Rail-Highway Crossings.
Numerous index formulas have been developed to assess the relative conflict potential at railroad-highway grade crossings based on various combinations of its characteristics. Although no single formula has universal acceptance, each has its own values in establishing an index. When used with sound engineering judgment, each formula provides a basis for a selection of the type of warning devices to be installed at a given crossing.
The geometric design of a railroad-highway grade crossing involves the elements of alignment, profile, sight distance, and cross-section. The appropriate design may vary with the type of warning device used. Where signs and pavement markings are the only means of warning, the roadways should cross the railroad, at or nearly at, right angles. Even when flashing lights or automatic gates are used, small intersection angles should be avoided. Regardless of the type of control, the roadway gradient should be flat at, and adjacent to, the railroad crossing to permit vehicles to stop when necessary, and then proceed across the tracks without difficulty.
13.11.4 Sight Distance
Sight distance is a primary consideration at crossings without train-activated warning devices. For a complete discussion of sight distance at grade crossings, refer to
and
. Refer to
for sight distance calculations.