Grade separation means trains and road vehicles cross each other on separate levels. This includes the different varieties such as a track bridge over the roadway or an road underpass through the tracks.
The benefits of grade separation include zero possibility of auto-train collisions, reduced traffic congestion, no horn noise, and ability of running more trains without impacting on cross traffic. However grade separation can be costly and if poorly planned, disruptive to the communities during the construction.
Types of grade separation
|Road over tracks||Mathilda Ave in Sunnyvale
San Antonio Road in Mountain View
|Little impact on train operation during construction.||Wider impact on areas further away from the tracks. Not bike/ped friendly.|
|Road under tracks||Jefferson Ave in Redwood City, Hillcrest Blvd in Milbrae||Zero visual impact. Lesser impact during construction. No shoofly during construction of Hillcrest Blvd||More properties may have no or limited access to road. Not as bike/ped friendly.|
|Tracks over road (no road depression)||Brittan Ave in San Carlos. Quint Street in San Francisco||Less impact on access for surrounding properties. More bike/ped friendly.||Greater visual impact. Longer shoofly tracks during construction.|
|Tracks under road||23rd Street in San Francisco||Zero visual impact. More bike/ped friendly. Less impact on access for surrounding properties.||Longer shoofly tracks during construction. High cost. Infeasible in some areas due to waterways.|
|Hybrid (tracks over the road and depressed roadway)||42nd Avenue in San Mateo.||Less impact on access for surrounding properties. More bike/ped friendly. Not as long shoofly tracks during construction.||Visual impact.|
Shoofly – temporary tracks
Grade separation considerations
Even though it may seem putting tracks in a trench is a good idea at first, feasibility and cost are dependent on the length of the grade separations, surrounding land use, and other features such as creeks crossing the tracks. In San Bruno, the grade separation is a hybrid one because the BART subway next to the Caltrain tracks do not allow the roadways to go all the way under nor allow the trains to be in a trench. Tracks cannot go all the way over the roads because of the I-380 over pass nearby.
Generally putting trains fully above or underground will require a longer structure (and longer shoofly during construction) because trains require a flatter grade than automobiles. If the area has several crossings that span a few miles then all of them would have to done at the same time. This could be difficult if the area has an existing auto over or underpass, or any waterway. The hybrid option would help reduce the length needed for the trains by lowering the roadway a bit.
Putting a automobile overpass above the tracks does not involve any shoofly. Some auto underpass constructions also do not involve shoofly. Shoofly require a wider right of way during construction.