Posts about Bioretention
Capitol Hill residents recently reviewed traffic-calming options for C Street, NE including separated bike paths ("cycle tracks"), reducing lanes, bulb-outs, "chicanes" where the road curves from side to side, reconfigured intersections, medians, stormwater bioretention araes, and more.
From Toole Design.
C Street, NE through northeastern Capitol Hill serves two roles. It's a neighborhood street with houses and a school, but it's also a major westbound route from the East Capitol Street bridge toward the Capitol and downtown.
In the morning peak, it carries high volumes of traffic. At other times, it has many fewer cars, but the wide configuration encourages them to speed.
At the request of residents, DDOT engaged Toole Design, one of the best local transportation firms, to study alternatives. They found that the wide roadway could become much more, even preserving the ability of the street to move many cars.
All options maintain the existing treebox areas, then place protected bike lanes inside the current curbs, but elevated to sidewalk level. Additional pedestrian and/or planted spaces (in red on the diagrams) then protect the lanes from traffic and parking.
North Carolina Avenue would get an eastbound cycle track and retain its westbound bike lane, while the westbound cycle track would continue on the one-way portion of C Street west of 16th Street and transition to a standard bike lane as the road narrows past 15th.
The largest difference between options is in the numbers of vehicular lanes. All reduce the eastbound lanes to one, as there is little eastbound traffic. Instead, drivers generally use Independence Avenue. For westbound cars, option A preserves the current three lanes and parking. B would preserve the three lanes in the peak but use the space for off-peak parking only, and C reduces the travel lanes to two with full-time parking.
In the center, a planted median would separate the two directions of traffic and provide left turn pockets. Each alternative includes a chicane, gently curving the road back and forth, either at a gentle 3000-foot radius or a narrower and more traffic-slowing 600-foot radius. The medians also prevent cars from crossing over C on smaller cross streets such as 17th Place, 18th Street, and 20th Street.
Raised crosswalks would slow traffic on cross streets to assist pedestrians. To the west, there is an option to reconfigure the intersection of Constitution and North Carolina to create one large island instead of several small ones.
Options for the intersection of Constitution and North Carolina Avenues.
Finally, the proposals contain significant "green streets" elements. The cycle tracks and new pedestrian paces in red would use permeable paving to minimize stormwater runoff. In addition, where there are large bulb-outs (also in red), Toole proposes bioretention areas, planted areas that are left more wild than manicured and can hold water like miniature wetlands during and after storms, letting it slowly drain into the ground rather than overloading storm sewers.
This project could create DC's first real "green street" and show how good design can do so much more with public spaces. I'm just disappointed we aren't getting the same for projects like 17th Street, NW, now under construction. Fortunately, the new DDOT is using Toole for several other ongoing projects, boding well for more designs like this to come.
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