LID opportunities in road-right-of-ways

File:Anatomy of a green street.png

Anatomy of a green street (Source: Ann English)

ROW standards in Ontario vary by municipality, but generally there are seven typical ROW types:

• Local residential road
• Residential collector road
• Local industrial road
• Industrial collector road
• Minor arterial
• Major arterial road
• High density commercial road

The characteristics, LID opportunities and constraints, and examples are presented for each of these ROW types on the following pages. Typical LID options for each of these street types are offered. However, this guidance is not intended to be prohibitive of other LID options, but rather to help reduce the number of LID options in the preliminary phases of screening and alert the designer to LID opportunities unique to that road type. Other considerations such as adjacent landuses, traffic demands, utility locations, budget constrains and geological conditions will determine the most appropriate LID solution.

Local residential road

Rural Cross-Section

Residential Road (Rural Cross-Section) and applicable LID options

Local residential streets are the most common street type. They serve as access to the residential lots within those areas created by, or bounded by, thoroughfares, arterials, collectors,and primary residential streets and other physical boundaries such as natural streams and railroads. Since the primary function is local vehicular access rather than intercommunity circulation, theses roads have low traffic volumes and mostly lightweight vehicular traffic, but they must accommodate the rapid access needs of emergency vehicles. Other characteristics specific to the residential rural cross section include:

• Shoulders are grassed, gravel, or bare soil from winter maintenance, pedestrians and street side parking
• Side drainage ditches are often narrow, poorly graded,and can be difficult for homeowners to maintain
• Utilities are often in separate trenches rather than a combined utility trench

Typical opportunities for rural cross section

Within the roadway:

• Use of permeable pavement within the roadway is not economical when there are adjacent swales to filter and infiltrate runoff

Within the boulevard:

• Bioswales or the use of perforated pipes beneath grass swales can reduce the nuisance problems associated with conventional swales like standing surface water and steep slopes
• Permeable pavement systems can be used to stabilize and improve degraded shoulders
• Converting degraded ditches to enhanced grass swales is the simplest LID improvement to make to residential rural cross-section roads. Driveway culverts can be slightly raised to provide storage and encourage infiltration

Urban Cross-Section

Local residential road (urban cross-section) and applicable LID options

Characteristics specific to the urban cross section include:

• Parking zones are often underused
• Residential boulevard space is the easiest to modify and use for stormwater management compared to other street types
• Utility lines may be in separate or shared trenches

Typical LID opportunities

Within the roadway:

• Curb extension bioretention is a good method for calming traffic and using underutilized parking zones
• Due to low speeds and low traffic, permeable pavement can be used for the roadway from curb to curb

Within the boulevard:

• Boulevard bioretention can be easily incorporated into a rural to urban upgrade by allowing for stormwater treatment within the boulevard space

Residential collector road

Cross section of a residential collector road

The function of these streets is to act as connectors between residential neighborhoods and other collectors and arterials. The character of these streets can vary widely from completely residential to pockets of commercial or mixed use land uses. Other characteristics include:

• Moderate to high traffic volumes, average daily traffic 1500 to 3000 vehicles
• Street parking is atypical unless there are adjacent mixed uses.
• Often have multi-modal use, transit, pedestrian, and cyclists
• Institutions such as schools, recreational facilities, and churches are often located along collectors

Typical LID opportunities

Within the roadway:

• Permeable pavement should be avoided for high traffic travel lanes, but they are an option for parking lanes

and sidewalk. However, permeable pavers are susceptible to clogging if receiving runoff drainage from adjoining asphalt roadway. Pervious concrete or porous asphalt are options for bike lanes.

• Perforated pipes are suitable for collectors with very limited space and particularly where there is no routine landscaping maintenance. However, adequate pretreatment such as grass swales, extended sump catchbasins, or prefabricated units must be provided.
• Curb extension bioretention is not a common practice for collectors, but they can be used in some cases to reduce pedestrian crossing distances at intersections

Within the boulevard:

• Collectors with few driveway access points and continuous stretches of open boulevard space are good candidates for bioswales
• Institutional uses along collectors offer opportunities for innovative LID solutions. Runoff can be treated within adjacent park space or on school properties where agreements have been made with school boards. These areas are also good opportunities for LID showcases or demonstrations.

Local Industrial road

LID options for the local industrial road

The function of local industrial roads is to provide access to industry and other employment zones. The ability to provide access and easy movement for large vehicles are a primary design characteristic of these types of streets. They are two to three lanes and are not intended for through traffic. Other characteristics include:

• Traffic volumes may be low but the road must still be wide enough to accommodate large vehicle turning movements and have increased structural strength to support heavy loads
• To avoid interference with truck movements landscaping should be low, and trees should be high branching or setback from the roadway
• Boulevards are often wide allowing for swale or other landscape treatment options

Typical LID opportunities

Within the roadway:

• Consideration should be given for wide turning trucks which may encroach on and degrade landscaping or road shoulders. Grid paver systems or widened gravel shoulders near turning areas can be used to accommodate occasional encroachment.

Within the boulevard:

• LID options for local industrial roads will heavily depend on the adjacent industries. For example, bioswales and other filtering practices may clog quickly where heavy industry like concrete mixing plants will track sediment onto the roads. Grass swales with sediment traps or prefabricated oil/grit separators which can be cleaned out on a frequent routine basis would be appropriate. Conversely, bioswales and perforated pipe can work well in areas of light industrial and commercial landuses.

High density commercial road

Go back to Screening LID Options

A road on which traffic movement and access to property have similar importance.

A road primarily for through traffic.

Low Impact Development. A stormwater management strategy that seeks to mitigate the impacts of increased urban runoff and stormwater pollution by managing it as close to its source as possible. It comprises a set of site design approaches and small scale stormwater management practices that promote the use of natural systems for infiltration and evapotranspiration, and rainwater harvesting.

An alternative practice to traditional impervious pavement, prevents the generation of runoff by allowing precipitation falling on the surface to infiltrate through the surface course into an underlying stone reservoir and, where suitable conditions exist, into the native soil.

A shallow constructed channel, often grass-lined, which is used as an alternative to curb and channel, or as a pretreatment to other measures. Swales are generally characterized by a broad top width to depth ratio and gentle grades.

The portion of water precipitated onto a catchment area, which then flows as surface discharge from the catchment area past a specified point.

Water from rain, snow melt, or irrigation that flows over the land surface.

Linear bioretention cell designed to convey, treat and attenuate stormwater runoff. The engineered filter media soil mixture and vegetation slows the runoff water to allow sedimentation, filtration through the root zone, evapotranspiration, and infiltration into the underlying native soil.

A shallow constructed channel, often grass-lined, which is used as an alternative to curb and channel, or as a pretreatment to other measures. Swales are generally characterized by a broad top width to depth ratio and gentle grades.

Vegetated, open channels designed to convey, treat and attenuate runoff. Design variations range from simple grass channels, which are designed primarily for conveyance to more complex treatment and volume reduction designs like enhanced grass swales, and dry swales or bioswales.

An alternative practice to traditional impervious pavement, prevents the generation of runoff by allowing precipitation falling on the surface to infiltrate through the surface course into an underlying stone reservoir and, where suitable conditions exist, into the native soil.

The slow movement of water into or through a soil or drainage system.

Penetration of water through the ground surface.

A shallow excavated surface depression containing prepared filter media, mulch, and planted with selected vegetation.

A mixture of mineral aggregates bound with bituminous materials, used in the construction and maintenance of paved surfaces.

Initial capturing and removal of unwanted contaminants, such as debris, sediment, leaves and pollutants, from stormwater before reaching a best management practice; Examples include, settling forebays, vegetated filter strips and gravel diaphragms.

Linear bioretention cell designed to convey, treat and attenuate stormwater runoff. The engineered filter media soil mixture and vegetation slows the runoff water to allow sedimentation, filtration through the root zone, evapotranspiration, and infiltration into the underlying native soil.

The portion of water precipitated onto a catchment area, which then flows as surface discharge from the catchment area past a specified point.

Water from rain, snow melt, or irrigation that flows over the land surface.

A shallow constructed channel, often grass-lined, which is used as an alternative to curb and channel, or as a pretreatment to other measures. Swales are generally characterized by a broad top width to depth ratio and gentle grades.

Soil, sand and minerals washed from land into water, usually after rain. They pile up in reservoirs, rivers and harbors, destroying fish-nesting areas and holes of water animals and cloud the water so that needed sunlight might not reach aquatic plans. Careless farming, mining and building activities will expose sediment materials, allowing them to be washed off the land after rainfalls.

A shallow constructed channel, often grass-lined, which is used as an alternative to curb and channel, or as a pretreatment to other measures. Swales are generally characterized by a broad top width to depth ratio and gentle grades.

Vegetated, open channels designed to convey, treat and attenuate runoff. Design variations range from simple grass channels, which are designed primarily for conveyance to more complex treatment and volume reduction designs like enhanced grass swales, and dry swales or bioswales.