Installation of the apparently relatively simple roadbed and rails of at grade systems in the center of existing streets and medians creates many unseen problems. The relocation of existing underground utilities and drainage systems can greatly increase the cost of construction and delay the implementation of such systems. In some cases, the installation of the at grade rail system affects surface storm flows and requires construction of additional drainage systems to prevent flooding of traffic lanes.
In many areas, at grade construction requires the removal of a large amount of existing material and its replacement with specific materials designed for tracked roadbeds, including placement of rubberized materials to reduce transmission of the vibrations of the rail commuter traffic to adjacent properties.
Wherever track alignment must leave surface streets, construction requirements and difficulties may escalate; particularly when rails must pass over, or under existing streets, highways or freeways. Such grade separating design and construction represent the most expensive and time-consuming components of at grade rail installation projects.
Alignments which pass through residential areas, whether within streets or not, require extensive screenings, sound walls and other mitigation measures to reduce the negative impacts of trains as they pass through these environments and settings.
Grade separation structures, generally utilized to avoid conflict with existing streets and automobile traffic, tend to be massive structures resembling highway overpasses or freeway transition ramps. In order to maintain the track grade required for efficient train operation, the structures and elevated roadbeds of grade separation structures must extend hundreds of feet on either side of the elevated crossing or underpass. A typical example of this design can be observed where the Los Angeles Expo Line is elevated to pass over La Brea Avenue, as the rail line runs in an abandoned railroad right of way.
Where at grade rail lines intersect cross streets, either at existing intersections or new locations, crossing gates are often required for safety and traffic circulation control. Such facilities, often including pedestrian crossing gates as well, cost well over one million dollars per crossing to install, and must be rigorously maintained. Where the speed of trains passing across minor streets at grade is kept to low enough speeds, rail system operators can elect to exclude crossing gates from intersections, but must employ traffic signals, warning horns, bells and lights adequate to maintain safety and avoid collisions with vehicles and pedestrians. A recently completed at grade rail system which operates without grossing gates can be observed on the eastern section of the East Los Angeles Gold Line Extension.
