The Westside Subway Extension is a big, complicated project that has been discussed in Los Angeles in one form or another for the past 50 years. Planning for the current project got underway in 2007 and is now in the final environmental review stage.

The Source is launching a new series called “Subway Facts & History” to address some of the issues generating discussion involving the subway project. The facts below are based on information from Metro staff and consultants planning the project. The information, in various forms, has already been publicly released.

Part one of the series will look at what can be built above subway tunnels and stations since the subway does not travel exclusively under city streets. It’s an especially hot topic because one of the subway routes under study by Metro would require tunnels to travel under parts of the Beverly Hills High School campus.

•Current Metro subway tunnels run under numerous buildings that were there long before the subway was built. The slide below shows just one place where the current subway runs under private property.

•Metro must pay for an easement to tunnel beneath any property. Any impacts to future development of a property would be part of the easement negotiation. Here’s a property acquisition fact sheet with more information.

•The right-of-way for the tunnels would extend 10 feet from the top of the tunnel — not all the way to the surface. In other words, the easement prevents structures from being built within 10 feet of the top of the tunnels.

•It is possible and legal to build new or to rebuild, remodel and retrofit buildings that sit over subways, although some special engineering may be required. The above rendering shows a residential building that is currently being built atop the subway in the Westlake part of Los Angeles.

•Whether the tunnels are built before new development occurs, at the same time or after, Metro typically works with the developer to ensure that both can be accommodated.

•Metro has asked property owners along the subway routes under consideration for information about their buildings, including their foundations. Such a request was also made of the Beverly Hills Unified School District about current high school buildings as well as redevelopment plans for the school.

•The image below (click to see a larger image) shows possible tunnel alignments in the area. It was shown to the community at meetings this past March. If the subway runs under Beverly Hills High property along this alignment, the tops of the tunnels would be approximately 45 to 60 feet below the ground elevation, which varies with the topography of the Beverly Hills High School site.

•There are rail tunnels and stations below schools in other U.S. cities. In California these include West Portal Elementary School and Marshall Elementary School, both in San Francisco, the Bentley School in Berkeley and Young Oak Kim Academy Middle School here in Los Angeles. Some schools outside of California include East Sylvan Middle School in Portland, Ore., Jefferson Middle School and Woodrow Wilson High School in Washington D.C. and the Global Village School in Decatur, Georgia.

•Last fall’s Draft Environmental Impact Statement/Report for the subway included geotechnical information gathered up to that point.

•Since then, Metro has performed additional ground tests on the Beverly Hills High campus and in the surrounding areas but is still reviewing the test results. The latest field test advisory is posted on the project’s web page.

•Tests were conducted on soil conditions, noise and vibration impacts, scanning for active and inactive gas and oil wells and water levels.

•Seismic testing was also done to learn more about two known seismic features in the area — the Santa Monica Fault and the West Beverly Hills Lineament.

•All of this testing and property data is being reviewed by geologists, engineers and other experts and will be shared publicly when the project’s Final Environmental Impact Statement/Report is released, which is scheduled for this fall. That document may also propose some changes to the tunnel alignments currently shown.

•Metro is unaware of any complaints about noise or vibrations from existing residences and commercial properties above the current Red and Purple Line subway tunnels. The buildings include those built before and after the subway opened.

•To prevent the ground from settling during tunneling, most urban tunneling around the world these days uses pressurized-face tunnel boring machines. The machines maintain pressure in the surrounding ground while pre-cast pieces of the concrete tunnel lining are installed. Metro used this type of machine to excavate the 1.8-mile tunnels for the Gold Line Eastside Extension where there was no measurable ground surface settlement or any substantiated property damage claims. The City of Los Angeles also used this type of machine for their East Central Interceptor Sewer that runs under parts of Exposition Boulevard.