Cities, counties, and local agencies are promoting sustainable development and capital improvements in a variety of different ways. Low impact design (LID) related to stormwater infiltration and treatment is a common goal. As noted previously, San Mateo County’s Sustainable Green Streets and Parking Lots Design Guidebook is a notable resource and reference. SB 790 and other State and Federal regulations can be expected to promote and likely require such treatment of stormwater runoff in the near future. However, current State highway design standards require complete drainage of stormwater.
Street improvements should incorporate stormwater infiltration and biofiltration features wherever feasible. Figure 5-24 depicts a basic street improvement condition (i.e. widened sidewalk, consistent shade trees, ornamental streetlights) with stormwater infiltration features. These include: a) pervious paving, structural soil, and appropriate subsurface drainage facilities within the curbside amenity zone; b) a “rain garden” bulb-out with drainage inlets and subsurface drainage facilities, and: c) pervious paving with subsurface drainage facilities in the parking zone.
Dining within the right-of-way as depicted requires sidewalk relinquishment; Caltrans typically requires a minimum relinquishment of 1 to 2 blocks.