Nov 192011
 

Planners are trying to figure out how to connect the Capital Crescent Trail (on a trestle) to the Rock Creek Trail 40 feet below.

Here’s my solution:

Note the 85% grade

Thank you Photoshop.  Actually the Planning Board recommends a switchback ramp system at a cost of $1.4M.   I’ve labeled it “switchback chosen” on this planning diagram“A new option” is my own (inferior) path idea, which adds about 1/3 mile for CCT users coming from the west.   Not shown is another option, putting a path along Jones Mill Road from the CCT south to the park.

Jack Cochrane
Chair, MoBike

 

  5 Responses to “Another trail crossing idea”

  1. Jack:

    Your new option looks good on an overhead view, but I fear it will not look so good on an elevation drawing.

    The rebuilt trail will not cross Rock Creek on a level path as it does now, but will drop down on and approx. 3 percent grade from Jones Mill Road to Rock Creek, to be about 30′ lower than it is now where it crosses Rock Creek on a new trail bridge. It will then climb at an approx. 3 percent grade to behind the apartment buildings east of the Park.

    Your new option would connect to the rebuilt trail where its elevation is about 30′ higher than would the “switchback chosen” option. I’m not sure it can even climb that high within the approx 1000′ length your route would have within a 5 percent grade, but to do so it would have to start climing immediately. That means you would have to build it almost entirely on the side of the railroad berm, you cannot just cross the meadow to start the climb. If your ramp has to be almost entirely on the side of the berm, the cost and environmental advantages go away, or even become reversed.

    On your path, trail users climbing the ramp and turning to take the rebuilt CCT west would climb and extra 30′, only to turn and give it all back as they follow the rebuilt CCT down to its lowest elevation over Rock Creek. The “switchback chosen” option would meet the rebuilt CCT near its lowest point to avoid this problem.

    I agree $1.4M appears to be a lot to pay for a switchback connection, but nonetheless I think the “switchback chosen” is on the best route.

  2. Wayne, thanks for this excellent explanation. So will there be a new trail bridge lower than the existing bridge on every option, even the Susanna Lane option? Thank you for the correction on the grade number. On the Planning Board’s recommended solution, is the grade on the actual switchback ramp limited to 3%? The relatively new bike/ped bridge in Rockville over I-270 has a 5% grade if memory serves. Well, $1.4M probably isn’t such a big deal given the use of these two trails. It would buy about a mile of the Matthew Henson Trail, but only 1/6 of the RC trail bridge over Veirs Mill Road (which is justified), and (I’m guessing) the comparable link from the ICC trail to the Matthew Henson Trail (which is justified).

    • Jack:

      Yes, every option shown so far will have the new trail bridge lower than the existing trail bridge.

      I finally jogged my memory to recall where I had seen the elevation drawing of the proposed Rock Creek crossing. It is in the set of drawings the MTA left with the CCCT at their Sept. 13, 2010 meeting. It shows the elevation of the rebuilt trail to be 214′ at its lowest point directly over Rock Creek. The surface of Rock Creek shows at 175′ in that drawing. The rebuilt trail is shown to follow a 3.87% slope as it travels east, and at 1000′ east of Rock Creek it is at elevation 250′ and still climbing. This is about where your new option would meet the CCT.

      The grade of the trail going west from over Rock Creek and toward Bethesda is shown as 2.25%

      The elevation difference between the trail it is lowest point over Rock Creek, and behind the apartment buildings 1000′ to the east, is shown in the drawings as 36′.

      These are only concept drawings and will change as the design proceeds. These same drawings confidently show the trail being in the Bethesda tunnel above the Purple Line, and we are seeing how that is working out! But the drawings also show the elevations of the existing groundline, and that groundline will always give us a similar problem with any RCT/CCT connection that chases the grade to the east.

      • The “other idea” I refer to in the title is climbing wall shown in the photo, not the ground options which I suppose we have to keep around for people afraid of heights. You can even rent those walls! Think of the savings.

  3. Don’t forget the zip line, Jack.

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