Several years ago, as the Silver line was being planned, there was a debate about whether to build the line underground through Tysons Corner. Eventually, the elevated option was selected, but there’s still a tunnel. Reader Dennis McGarry wants to know why.
Why is there a short tunnel on the Silver Line with no underground stops? Why not just build the entire track above ground? It seems like such a huge undertaking with little payback.
There are two short tunnels in Tysons (one for each track). They run about 1700 feet between Tysons Corner station and Greensboro station. The reason they exist is to cut through the highest point in Fairfax County, at 520 feet above sea level.
The tracks through Tysons are already high above the streets, and the climb between McLean and Tysons Corner is noticeable, especially from the front of a westbound train. Because trains are limited in the grade they can ascend, crossing this hill with an elevated viaduct would make the stations at Tysons Corner and McLean obscenely high.
In addition to the engineering and aesthetic challenges that a super-high viaduct would have caused, trying to keep the line elevated would have probably been much more expensive. So it was probably cheaper for the contractor to build these short tunnels than it would have been to keep the line elevated over the hill.
As a result, riders at McLean get a soaring view of the Tysons skyline (and in fact, you can see Bethesda, too), but a few minutes later, they find themselves riding underground, ever so briefly.