Smith 9th st elevated F train question

[BobLI]

Why was the subway elevated at that stop and also 4th ave and then go back underground?

Too much ground water in the area for a tunnel? And also why does it then go elevated at Ditmas for the rest of the trip? Cheap construction verses tunnel?

Thanks for all the replies.

[Allan]

Why was the subway elevated at that stop and also 4th ave and then go back underground?

Too much ground water in the area for a tunnel? And also why does it then go elevated at Ditmas for the rest of the trip? Cheap construction verses tunnel?

Thanks for all the replies.

You've got the general idea on the Smith-9th St station.

Why does it go elevated at Ditmas? For one thing that structure was already there built by the BRT/BMT and opened in 1919 as part of the elevated system in Brooklyn.

The IND line (ending at Church Av) was built by the City of NY and opened in 1933. Keep in mind that the BMT and IND were separate systems. (BRT/BMT - private operator, IND operated by the City of NY)

When the City of NY took over the operations of the the the IRT and BMT systems in 1940, there were plans to extend the Church Av line to the BMT Culver line structure (a concrete ramp was started) but it was interrupted by WWII. The work resumed in the early 1950s and completed in 1954.

For reference: http://www.nycsubway.org/perl/stations?212:212120

[Gerry6309]

The use of els and tunnels in the Smith-9th area is also driven by economics. To keep the subway near street level for cut & cover construction, the tunnel runs upgrade from Bergen St. south. When the terrain starts to drop, the subway grade remains constant until it levels out at Smith-9th. After crossing the Gowanus Canal, the local grade again rises, and the line goes underground again as it crosses 4th Av. It was much easier to cross the Gowanus on a bridge than to tunnel beneath it, and build about a mile of tunnel under Smith, followed by a very deep bore under 4th Av. and the ridge to the east. Much easier, thus cheaper to build. (Which meant more money available for other purposes. )

[BobLI]

Thank you for the answers.