A level crossing is an intersection where a railway line crosses a road or path, at the same level. Or in rare situations an airport runway. As opposed to the railway line crossing over or under using an overpass or tunnel. The term also applies when a light rail line with a separate right-of-way or reserved track crosses a road in the same fashion. Level crossings are ideal railway/highway at-grade crossing is designed to fulfill its primary purpose. That is establishing a smooth surface while providing for the safe passage of rubber-tired vehicles across railroad tracks.
EVEN AT-GRADE CROSSINGS
The design of at-grade highway intersections and highway-railroad grade crossings is frequently complex and problematic. They requiring the designer to examine and respond to many different factors and issues. Their design when both are in close proximity is even more problematic. Designers must respond to physical constraints that sometimes require clearances between the railroad and the parallel roadway edge to be reduced. They affect alignment and traffic control devices. Traffic control systems may have to be interconnected to work properly, and warning systems related to the at-grade intersection may conflict or distract from systems related to the highway-railroad grade crossing.
In the field of transportation, highway-rail grade crossings are unique because they are intermodal intersections. Unlike intra-modal intersections, where vehicles/trains from adjacent approaches take turns traversing the crossing, trains have the right of way through highway-rail grade crossings. Trains have been given the right-of-way because of their character and momentum. Vehicular traffic must yield to trains at every grade crossing every time and may not proceed until all trains have cleared the intersection.
The history of level crossings depends on the location, but often early level crossings had a flagman in a nearby booth who would, on the approach of a train, wave a red flag or lantern to stop all traffic and clear the tracks. Gated crossings became commonplace in many areas. As they protected the railway from people trespassing and livestock. Also, they protected the users of the crossing when closed by the signalman/gateman. Manual or electrical closable gates barricaded the roadway started to be introduced. Intended to be a complete barrier against intrusion of any road traffic onto the railway.
Automatic even at-grade railroad crossing is now commonplace in some countries as motor vehicles replaced horse-drawn vehicles and the need for animal protection diminished with time. Full, half, or no barrier crossings superseded gated crossings, although crossings of older types can still be found in places. In rural regions with sparse traffic, the least expensive type of level crossing to operate is one without flagmen or gates, with only a warning signposted. This type has been common across North America and in many developing countries.
TRAFFIC CONTROL DEVICES
Traffic control devices (TCDs) are present at highway-rail grade crossings to remind highway users that they must stop for trains. Several levels of traffic control at highway-railroad grade crossings, divided primarily into passive and active control devices. The most basic of these devices, passive devices, provide static messages of warning, guidance, and perhaps action required by the driver. Among these passive devices are signs and pavement markings.
For more advanced traffic control, active control devices are necessary. These devices give warning of the approach or presence of a train. They are activated by the passage of a train over a detection circuit in the track. One of the most predominant forms of active traffic control is the use of automatic gates. Which physically block the travel lanes and are used in conjunction with flashing lights. Active control devices are supplemented by the same signs and markings used in the passive control.
SAFETY AND MANAGEMENT
Highway/railway at-grade crossings mark the convergence of two of the most critical portions of the transportation network. For this reason, it is essential that the quality of these crossings is maintained. However, maintaining crossing quality is not an easy task. Due to the combination of highway and railroad traffic, at-grade crossings are exposed repetitively to heavy loads carried by passing trains and trucks. As a result, the settlement at these crossings occurs quickly. Settlement greatly affects the quality of the crossing by increasing its surface roughness. Which negatively impacts the motoring public and railroads alike. Crossing roughness can be attributed to the roughness of either the highway approach or the immediate crossing surface.
Rough crossings caused by excessive settlement adversely affect railroad operations by potentially slowing trains. These increasing slow orders and increasing maintenance costs. In addition, settlement places in jeopardy the safe movement of trains over crossings because excessive settlement affects the geometric features of the rail line, which increases the likelihood of derailments. Vehicular traffic is affected similarly. Rough crossings not only create undesirable driving conditions but may also contribute to heightened safety problems. At-grade crossings remain hazardous despite drastic industry-wide safety improvements over the past 40 years.
Minimizing crossing roughness improves the operating efficiency of train and vehicular traffic. Limiting the deceleration of trains near at-grade crossings reduces fuel consumption and minimizes company and consumer costs. Likewise, delays caused by at-grade crossings can impose significant costs in terms of loss of time and energy for vehicular traffic. As railroad and highway volumes continue to mount, the prevalence of rough crossings will increase unless new standards for at-grade crossing rehabilitation and renewal are established.