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Concepts For a Shared Rail/Road Bridge

June 10, 2012
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In our previous article we discussed the benefit of combining a vehicular and rail crossing located near the CIA facility. The bridge should provide a compact design that would reduce the impact to the natural environment of the Potomac. It would be the most environmentally sensitive to have no mid-river piers, therefore a cable stayed system with land piers should be preferred. Here is a quick mock up of what the transportation segments would look like.

Cable stayed bridges provide little benefit in the case of a road bridge for river crossings, beyond aesthetics, as in most cases the simpler and more economical choice is a standard pier and deck system. When a much more demanding live load from a heavy rail system is included the cable stay provides an efficient method of addressing the new structural requirements. The cost per mile is increased but compared to two individual bridges this method would remain more efficient.

By providing a pedestrian/emergency vehicle road deck above the metro rail, the bridge width is reduced and a central corridor for emergency vehicles can be provided to address bridge incidents. This also provides a greater safety in the separation of vehicles and trains that can prevent intentional attacks on the rail tracks.

The bridge is designed to carry 6 vehicular lanes of 11′ each with a 3′ shoulder and 2′ curbed retaining wall. The cable stayed towers would need to be approximately 250′ above bridge deck, for a total height over water of approximately 350′. The elevation of the towers would be approximately 100′ above the side banks of the Potomac at this part of the river. Much of the towers could be screened with vegetation. Most importantly, while the towers might have a visual impact, the water body itself can remain undisturbed without mid-span piers.

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6 Responses to Concepts For a Shared Rail/Road Bridge

  1. Richard on January 23, 2013 at 5:21 pm

    Would work better as an extension of the purple line than a heavy rail option the capitol crescent trail could be used for a few miles of it as well.

    • Tysons Engineer on January 23, 2013 at 5:30 pm

      That is an excellent point. The reasoning behind the heavy was so that Orange line trains could be split, thereby reducing the need for the also necessary blue line tunnel. Just trying to kill two birds with one stone. Instead of increasing capacity of the current blue/orange crossing you could effectively reduce in half the number of orange line trains going through, and therefore increase the availability to the blue line trains.

      It would certainly be an improvement to the corridor with only LRT as well, and would cost a lot less for structural consideration of the bridge.

    • Richard on January 23, 2013 at 6:16 pm

      also running the line down 123 would better serve the community than down the center of 495

      • Tysons Engineer on January 23, 2013 at 6:22 pm

        Unfortunately, this is not a realistic alignment. There are several very expensive homes, a police station, several midrise offices along the Right of way (within 10-20′) of the paved surface.

        In order to run anything down Route 123 either 2 lanes would need to be removed from the 4 lane road… something that McLean residents would likely object to, or the entire system to be tunneled.

        Considering the system for Tysons which was being substantially paid for by Fed funds and private developers was rejected for tunneling due to a 10% increase in cost, it is unlikely a tunnel will be accepted.

        I agree with you though, it would be far better if it could simply run down the right of way of Route 123, but certain groups will never allow it.

  2. Matt on February 8, 2013 at 12:37 pm

    Almost any plan that helps put another bridge across the river inside the beltway is a good one! The fact that this connects the Red and Orange (Silver) lines before going all the way to Metro Center makes it even better!

  3. WFY on April 10, 2013 at 1:48 pm

    Are there that many Tysons to Bethesda trips though? I think a rail link between Tysons and the 270 corridor makes more sense.

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