Incorporating green infrastructure into transit street design can improve water quality, detain stormwater flows, reduce the volume of stormwater runoff, and relieve burden on municipal water treatment systems.
Green infrastructure can complement transit by calming traffic, enhancing comfort while waiting for transit, and creating opportunities for safer pedestrian crossing at bus bulbs and curb extensions with green infrastructure.
APPLICATION
Integrate green infrastructure into sidewalks, medians, curbs, and other features, including bioswales, flow-through planters, or pervious strips.
At stations and terminals, an enhanced landscape can improve aesthetic appearance, user comfort, and ecological performance.
BENEFITS
A tree canopy and green features can improve transit experience for waiting riders, increasing comfort and reducing perceived wait time.
Green infrastructure improves the natural ecosystem and reduces harmful pollutants. Where vehicles leave oil and other pollutants on the road surface, a bioswale facility can prevent large amounts of pollution from entering the watershed.
CONSIDERATIONS
Select appropriate plantings; in dry climates, drought-resistant landscaping (xeriscaping) reduces water and maintenance requirements.
Choose green infrastructure based on pedestrian volume and the intensity of use on a sidewalk.
RECOMMENDED
As required, install a perforated pipe at the base of the facility to collect the treated runoff.
Bioswales have a slight longitudinal slope that moves water along the surface to allow sediments and pollutants to settle out. In-place infiltration then allows localized groundwater to recharge. Ideal side slopes are 4:1, with a maximum slope of 3:1. Use a maximum 2% gentle side slope to direct water flow into the facility.Use appropriate media composition for soil construction. The engineered soil mixture should consist of 5% maximum clay content.
The planter should drain within 24 hours; this is especially critical near transit stops where pooling can degrade transit access.
Ensure that infiltration rates meet their minimum and maximum criteria. The engineered soil mixture should be designed to pass 5–10 inches of rain water per hour.
Where a near-side boarding bulb is combined with a turn restriction, design the curb to self-enforce the turn restriction and monitor closely to ensure that transit vehicles are not suffering from delays.