Johns Hopkins University

OPEN GALLERY

Highlights

• Site – 8 acres
• 1 mile of new and improved pedestrian walks
• 345-foot-long pedestrian bridge
• 12,909 sq ft of impervious area removed
• 750 sq ft of microbioretention
• 4,640 cu ft of stormwater treatment (exceeding the required 2,465 cu ft)
• 588 lf of bioswale

Perspectives

San Martin Drive is a historic roadway that defines the western edge of the campus. Winding along the steep Stony Run Valley, the forested drive is a critical north-south connection for pedestrians, cyclists, and vehicles. It is a natural asset, but also dangerous. Sharp bends offered poor sight distance, vehicles traveled too fast, and existing sidewalks abruptly ended, forcing pedestrians into the road.

Integrated planning began with a detailed site assessment. The design team identified areas of new forest plantings and easements, tree protection measures, and poor-condition trees to be removed for improved safety. A historic Olmsted stone arch bridge was determined to be too narrow to support a continuous sidewalk, resulting in the addition of a new elevated, 350-foot pedestrian bridge through the canopy. The team walked the woods to define the bridge alignment to preserve mature canopy trees. Challenging terrain and protected forest pushed the team to look at how stormwater facilities could be constructed in the city-owned right-of-way instead of on private property. The design team incorporated an interconnected system of bioswales to redirect and cleanse stormwater that otherwise carried pollutants into the watershed.

The forest preservation easements restricted excavation and canopy impacts, meaning traditional bridge foundations and construction techniques were not permitted. The team had to re-think how to lay out, design, and build a bridge. To solve this challenge, the team designed the bridge utilizing micropiles, which could be installed with equipment small enough to work around the trees and under the canopy. The bridge’s structural components were designed to be small and light enough to be erected utilizing a topdown approach, so that equipment would not work on the forest floor or impact tree roots.

The project transforms the corridor into an immersive walk through the woods on a pathway that preserves and enhances the natural ecology of the site, incorporates significant stormwater treatment measures, and solves significant pedestrian and vehicular safety issues by installing a variety of traffic calming measures, narrowing travel lanes, completing sidewalk gaps, and widening existing sidewalks.

Project Team

Ayers Saint Gross; also RK&K