The unprecedented increase in vehicular traffic in the past ten years and recent increases in transit and rail traffic lead to a major concern for safety and roadway/railway interfaces.
As grade crossings are evaluated, there comes a time when the logistics of maintaining the safety and integrity of a highway-rail grade crossing outweigh the cost of eliminating it. At that time the owner and designer need to select a grade separation structure type based on several considerations: traffic maintenance and control; construction staging; train scheduling; vehicular clearances; aesthetics; and, of course, economy. Many grade separation alternatives are available to solve the concerns of all those involved and responsible for the crossing.
The type of structure most commonly used is the bridge structure, which vertically separates the transportation modes such that one is raised over the other. The construction methods used to deploy this type of solution are many and often quite creative since the railway, or roadway, cannot be closed for extended periods of time, if at all.
Similar to this approach is another solution: the underpass. Typically, this type of structure enables the roadway to pass beneath existing railroad tracks. Another alternative is the railroad trench. One significant trench project has recently been constructed-see the Railroad Trench Structures section for more information.
Another unique approach to the construction of grade separations is tunnel jacking. Tunnel jacking is a technique of installing an access way-vehicular, pedestrian, or utility-beneath an existing facility, such as a roadway or railway, without disrupting the operations of that facility. In simple terms, the process involves constructing a concrete tunnel structure adjacent to the facility at a desired depth, and then "jacking" or horizontally pushing the preconstructed tunnel under the facility while simultaneously excavating the soil as the tunnel advances.
Considered an accepted practice in Canada, Europe, Australia, India, South
Africa, and the Far East, the use of tunnel jacking has been increasing
in the U.S.