The Transportation Research Board 92nd Annual Meeting is being held this week in Washington, D.C. This year there are nearly 12,000 attendees from around the world to participate in the more than 4,000 presentations covering all transportation modes and addressing topics of interests to all, including policy makers, administrators, researchers and practitioners.
A session on rail updates included a look at the use of green tracks for rail projects: replacing the standard ballasted track with green media. With the Maryland Transit Administration (MTA) looking for solutions to ever-increasing environmental regulations, Ken Schmidt of Mahan Rykiel talked about the Red Line Corridor Transit Study in Baltimore, Md.
As Schmidt described it, it’s like bringing green roof technology back down to the ground. The pilot project within the corridor is studying the effectiveness of using plant material between and along the rails instead of the traditional ballast.
Green tracks reduce pollutants, reduces runoff, reduces heat island, reduces noise, preserves green space, improves aesthetics and enhances habitat with pollinators.
Some specifics mentioned were that it is between 10 and 15 degrees lower than the adjacent pavement temperatures and the noise levels are 2 to 4 decibels lower than traditional ballast or slab construction.
The succulent plants retain water, so the team is coordinating with Maryland’s Department of the Environment (MDE) regarding stormwater management (SWM) credits.
Considerations
They looked at track design considerations for drainage, stability and maintenance, as well as different plants and media. While soil composition holds up fine for plants, it compacts from the vibration of rail, while a crushed recycled brick mix did not migrate and kept soil fairly loose.
For the plant establishment, the contractor provided a higher level of initial maintenance, minimal weeding and watering with no long-term maintenance. “We need something that’s going to be sustainable on its own,” Schmidt said.
The design team established monitoring protocol, including temperature readings and soil testing. It also provide monthly and thrice-yearly reporting.
Challenges and Surprises
There was some traffic that compacted the soil and wouldn’t let anything grow and that included footprints and car tire tracks. One test area had a lot of pedestrian traffic and sedums don’t like to be stepped on. At one of the test areas, after an art fest, someone drove on the green tracks, leaving the tire tracks.
Sedums hold a lot of water and the state of California uses them as fire suppression because they hold moisture. However, they found that while sedums can perform really well in hot and humid areas, many of those areas cool to 70 degrees or so at night. In Baltimore, the heat and humidity remains more consistent. Different plants respond to different weather site conditions, though rail activity had minimal impact on growth.
Going Forward
For environmental sustainability of rail projects, multi-disciplinary team collaboration is critical, including engineers, architects and landscape architects. Another key point Schmidt made was that public education and awareness needs to be elevated. Signage at test areas and information at community meetings needs to be a part of it and it needs to be stressed to the public that green tracks doesn’t mean grass; it’s not going to be manicured.
