Automatic Gates

An automatic gate serves as a barrier across the highway when a train is approaching or occupying the crossing. The gate is reflectorized with vertical red and white stripes. To enhance visibility during darkness, three red lights are placed on the gate arm. The light nearest to the tip remains steadily on; the other two flash alternately. The gate is combined with a standard flashing ‑light signal that provides additional warning before the arm starts to descend, while the gate arm is across the highway, and until the gate arm ascends to clearance. The gate mechanism is either supported on the same post with the flashing ‑light signal or separately mounted on a pedestal adjacent to the flashing ‑ light signal post. Additional guidance regarding these devices can be found in Chapter 3. In a normal sequence of operation, the flashing ‑light signals and the lights on the gate arm in its normal upright position are activated upon the detection or approach of a train. The MUTCD standard in Section 8C.04 requires that the gate arm should start its downward motion not less than 3 seconds after the signal lights start to operate, should reach its horizontal position before the arrival of the train, and should remain in that position while the train occupies the crossing. When the train clears the crossing, and no other train is approaching, the gate arm should ascend to its upright position normally in no more than 12 seconds, after which the flashing ‑lights and the lights on the gate arm should cease operation. In the design of individual installations, accommodations for large and/or slow-moving highway vehicles (regarding timing the operation of the gate arm) should be considered. Section 9.6 of the California Public Utilities Commission (CPUC) General Order 75-D requires that, when the gates are fully lowered, the gap between the ends of two complementary gates must be less than two feet. This CPUC General Order also requires that, if there is a median, centerline striping, or other form of channelization installed, the gap between the gate end and the channelization device must be within one foot.” Some railroads request reconfiguration of the crossing when gate arm lengths would exceed 32 feet and it may be necessary to place gate assemblies in the median to cover the approach highway, in which case a 9-foot wide median should be used to provide adequate clearance. In these cases, crash cushions or other safety barriers may be desirable. Under no circumstances should signals or gate assemblies be placed in an unprotected painted median. Conversely, some railroads would prefer longer gate arms rather than a gate mechanism in the median. When no train is approaching or occupying the crossing, the gate arm is held in a vertical position and the minimum clearance from the face of the vertical curb to the nearest part of the gate arm or signal is 2 feet, for 17 feet above the highway. Where there is no curb, a minimum horizontal clearance of 2 feet from the edge of a paved or surfaced shoulder is required per MUTCD 8C.01, with a minimum clearance of 6 feet from the edge of the traveled highway. Where there is no curb or shoulder, the minimum horizontal clearance from the traveled way is 6 feet. Where flashing ‑lights or gates are located in the median, additional width may be required to provide the minimum clearances for the counterweight support. It should be noted that gate arms have a maximum standard length of 32–38 feet, depending upon the railroad. 65The lateral location of flashing light and gate assemblies should provide adequate clearance from the track as well as space for construction of the foundations. (The area for the foundation and excavation should be analyzed to determine the effect on sidewalks, utility facilities, and drainage.) Figure 27 indicates current standards: It should be noted that commercially available components may encroach on the desired 10-foot clearance between the face of the device and center of rail, therefore a 12-foot setback may be inadequate. For these reasons, some railroads require a 15-foot minimum clearance. Figure 27. Typical Location of Signal Devices Source: Institute of Transportation Engineers. 66If it is necessary to locate the supporting post in a potentially hazardous position to ensure adequate visibility, some type of safety barrier should be considered. These are discussed in a later section. Large multilane intersections and intersections with unusual configurations should be carefully studied to determine the appropriate layout of crossing gate locations. For such conditions, gate arm requirements may become a principal factor in the layout of the intersection geometry and channelization from the outset. The crossing gate (and, therefore, traffic control) treatment should be an integral part of the design of an intersection, not an afterthought. Discussion on pedestrian treatments can be found in the Pedestrian Treatments section of this document.It is desirable to place crossing gates perpendicular to the direction of travel on the approach roadway. Figure 28 provides an illustrative example for an orthogonal crossing. The crossing gate mast should be 15 feet from the center of rail; where necessary, this distance can be reduced with concurrence from the railroad provided a minimum distance of 10 feet from the center of rail to the face of any part of the device is maintained. The crossing gate arm typically has a maximum length of 32 feet; if allowed by the railroad, longer gate arms may be used. At locations where the crossing is at a skew angle, the crossing gates need to be set back to be installed perpendicular to the roadway while meeting the required minimum 12-foot distance from the center of rail ( refer to Figure 29 and Figure 30 for obtuse and acute angled crossings, respectively). At locations where there is a frontage road intersection close to the crossing, it may not be possible to achieve a mounting perpendicular to the approach roadway and angling the crossing gates may be required as shown in Figure 31. Angled crossing gates reduce the size of the zone between the crossing gate and rail, and may be helpful to prevent vehicles from driving around the entry gates. Current retroreflective materials are activated over a very wide angle and should be visible at night; rotating the gates minimizes the area behind the gate and results in a shorter pedestrian zone behind the gates. Multi-lane highways typically require use of median-mounted crossing gates. A median-mounted gate may satisfy the criteria to have one set of flashing ‑light devices aimed at each approach lane. If there are three or more approach lanes, a cantilever is usually required. Examples showing use of medians with median gates and with the cantilever mounted upstream and downstream from the crossing gates are shown in Figure 32 and Figure 33, respectively. Refer to the subsequent topic Use of Channelization with Gates for more information on median treatments. Figure 28. Typical Crossing Gate Placement at 2-Lane Orthogonal Crossing Source: Institute of Transportation Engineers. Figure 29. Typical Crossing Gate Placement at Obtuse Angled Crossing Source: Institute of Transportation Engineers. Figure 30. Typical Crossing Gate Placement at Acute Angled Crossing Source: Institute of Transportation Engineers. Figure 31. Alternate Crossing Gate Placement at Acute Angled Crossing (Shown with Exit Gates) Source: Institute of Transportation Engineers. Figure 32. Typical Crossing Gate and Cantilever Placement at Multi-Lane Roadway with Medians and Median Gates—Cantilever Upstream from Gates Source: Institute of Transportation Engineers. Note: Location of crossing gate and cantilever may be switched Figure 33. Typical Crossing Gate and Cantilever Placement at Multi-Lane Roadway with Medians and Median Gates—Cantilever Downstream from Gates Source: Institute of Transportation Engineers. 70Four-Quadrant Gates Four-quadrant gate1 systems consist of a series of automatic flashing ‑light signals and gates in which the gates extend across all roadway lanes on both the approach and the departure side of the crossing. Unlike two-quadrant gate systems, four-quadrant gates provide additional visual constraints and inhibit most traffic movements over the crossing after the gates have been lowered. The use of four ‑ quadrant gates has increased significantly in the past decade for two main reasons: (1) design criteria adopted by transit and commuter rail operators which requires use of gates on all crossing approaches, and (2) “Quiet Zones” where four-quadrant gates have been used for risk reduction. There are two recognized methods for operation of the exit gates: timed or dynamic. In the first instance, exit gates operate on a delay timer to allow vehicles which pass by the entry gates to exit the crossing zone before the exit gates are lowered. In the second case, known as “dynamic exit gate operating mode,” an “exit gate management system” with detection loops in the crossing area is used to monitor vehicle presence within the crossing and hold open and/or raise the exit gates if vehicles are on the crossing after the entry gates are lowered. This second method is costlier to install and maintain but may be preferred at locations where the traffic flow rate is unpredictable to assure exit gates do not descend on vehicles. On the other hand, it is possible for a vehicle to back up into the vicinity of an exit gate loop and cause the gate to raise. It should be noted that some jurisdictions may require use of the dynamic operating mode by policy. Entry gates are designed to “fail-safe in the down position” (e.g., they are powered up and if the power fails, they will lower by gravity). However, the failure mode for exit gates is to “fail-safe in the up position” so that vehicles do not become trapped on the crossing in the event of a power failure. Additional guidance for Four-Quadrant Gate Systems operation can be found in MUTCD Section 8C.06. Four-quadrant gates are recognized as a “Supplemental Safety Measure” (SSM) in FRA regulations governing Quiet Zones (49 CFR Part 222, Appendix A). It should be noted that FRA has assigned a lower effectiveness rate to installations that include vehicle presence detection because the act of raising the exit gates may allow vehicles to enter the crossing. Figure 34 shows four quadrant gate treatments for various conditions. 1 Because of varying intersection configurations, not all crossings using exit gates have gates in all four quadrants; the term “Full Closure” is a broader characterization of crossings with gates to block exit lanes. 2 For example, the California Public Utilities Commission (CPUC) requires use of a vehicle presence system “subject to a Commission staff diagnostic field meeting recommendation and an engineering study performed by railroad or local agencies” (General Order 75 ‑D). Figure 34. Example of Location Plan for Flashing-Light Signals and Four-Quadrant Gates Source: Manual on Uniform Traffic Control Devices, 2009 Edition, Figure 8C-2, Washington, DC, FHWA, 2009. 72Barrier Gate The barrier gate is a movable automatic gate designed to close an approaching roadway temporarily at a highway-rail crossing (see Figure 35). A typical installation includes a housing containing electromechanical components that lower and raise the gate arm, the arm itself, and a locking assembly bolted to a concrete foundation to receive and hold the lowered gate arm in place. The barrier gate arm has been installed with a system consisting of three steel cables, the top and bottom of which are enclosed aluminum tubes. Figure 35. Example of a Resistance Barrier Source: B&B Roadway—Resistance Barrier. (n.d.). Retrieved July 17, 2018, from http://bbroadway.com/site/products/vt-6802hdtr/ Barrier devices should at least meet the evaluation criteria for a MASH(24) attenuator; stopping an empty 4,500-pound pickup truck traveling at 43 mph. Barrier gates have been tested to safely stop a pick-up truck traveling at 45 mph. Barrier gates could be applied to situations requiring a positive barrier, such as closing-off road traffic and opening crossings only on demand. FRA regulations(7) also require use of FRA- approved barrier and/or enhanced warning systems for train operation over 110 mph. FRA has indicated that a barrier gate, if equipped with monitoring device, may be used to enforce a nighttime closure for partial quiet zones.