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
• Main streets

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.

Industrial collector road

LID options for the industrial collector road

The function of industrial collectors is to provide efficient traffic flow, accomodation for large transport vehicles and access to industry and other employment land areas. These roads are typically four to five lanes and have wide boulevards. Other characteristics include:

• High profile industry is often located along industrial collectors and a high quality corporate landscape treatment is expected
• To avoid interference with truck movements landscaping near roads should be low and trees should be high branching or setback from the roadway

Typical LID opportunities

Within the roadway:

• Due to high traffic and heavy vehicles, LID options within the roadway are limited. Prefabricated sediment traps and perforated pipe with proper pretreatment are potential options.

Within the boulevard:

• Broad enhanced grass swales with perforated pipe can take advantage of wide boulevard spaces
• Any landscape based solutions must consider the landscaping expectations of adjacent properties both

with respect to aesthetics and maintenance. Some areas will have an expectation for a simple turf lawn frontage that can be easily incorporated into their maintenance, while other higher profile industrial areas will want distinctive signature landscapes with decorative plantings and shrubs.

Minor arterial

LID options for the minor arterial road

Minor arterial roads are automobile oriented roads intended to move high vehicle traffic volumes and are typically four lanes. Pedestrian and bicyclist accommodations are sometimes expected. Other common characteristics include:

• Boulevards are often wide but must accommodate sidewalks on both sides, street trees and splash pads
• May include narrow medians, but runoff is typically directed away from them to road sides

Typical LID opportunities

Within the roadway:

• Dedicated parking lanes or parking lay-bys can be converted to permeable pavers. The permeable parking lane can be designed to accept only the rainfall that falls on it or it can take runoff from up to two additional lanes.

Within the boulevard:

• Attractive bioretention planters and permeable paver sidewalks are appropriate for high density areas and where business districts expect an enhanced or signature streetscape.
• Street trees can be supported with LID options by providing root volume space in bioretention practices or with sidewalk support systems. Permeable sidewalks allow air and moisture to reach tree roots which in turn reduces sidewalk buckling from roots pushing through the surface.

Major arterial road

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Major Arterials are broad, four to six lanes, with an emphasis on speed, high volume vehicle flow and little on pedestrian or bicycle accommodation. Other characteristics include:

• Wide boulevards and large landscaped medians are common
• Due to higher travel speeds, maintaining clear zones and sight distances are critical

Typical LID opportunities

Within the roadway:

• Where possible, replace unnecessarily paved areas such as medians or traffic islands with pervious areas. If road grading allows, than these areas can be converted into treatment practices for surrounding impervious areas
• If the road is double crowned, then medians are an excellent place to treat arterial runoff with a simply landscaped bioretention or bioswales
• If road grades direct no runoff to the median, then reducing the median width and increasing the boulevard space would open more area for stormwater treatment along the side of the roads where the runoff drains
• Getting plants to survive may be difficult in narrow medians, consider decorative permeable paver solution over simply covering them with impervious asphalt or concrete

Within the boulevard:

• Bioretention planters are appropriate for high profile urban arterial roads, but they must be properly designed to handle flows from larger impervious areas and have easily cleaned pretreatment

Main streets

LID options for main streets

Main streets are set in areas with high density commercial, residential, and mixed use and are typically focal points of the community. The buildings have small to no setbacks and create a continuous wall along the street. They offer an opportunity to incorporate beautifying green infrastructure, but they are also a challenge for designers owing to the multiple demands of street parking, street trees, business access, above and below ground utilities, pedestrian accommodations, and vehicle movement. Depending on age and prominence these streets may have been reconstructed multiple times and have infrastructure legacy issues like abandoned utility lines. Other characteristics include:

• Street parking is typical and may have frequent turn over and is necessary for local business.
• ROW dimensions will vary greatly depending on the age of the community.

Typical LID opportunities

Multifunctional LID practices are favored where there is a premium on space. Bioretention planters can serve as both the landscape amenity of the street and treat stormwater. Permeable pavement serves as a treatment practice but is also a hardscape for parking and pedestrians.

Within the roadway:

• Curb extension bioretention can be used as traffic calming features and reduce pedestrian crossing distances.

Within the boulevard:

• Due to the high profile of this street type, they are maintained on a frequent basis and provide the most appropriate setting for an aesthetic bioretention feature.
• Street trees are high priorities for this road type and LID options should support or incorporate them by providing root volume space in bioretention practices or with sidewalk support systems.

Other Design Considerations

The previous sections presented the most common options based on the type of construction and the road type. The project team must use the information gathered through the background review Link field reconnaissance Link, feedback gained from the public engagementLink as well as from the LID practice Suitability & Considerations Comparison Table Link to determine the feasible and optimal LID options for the site. Below is a list of factors to be considered when choosing the type of practice and how it will be incorporated into the site:

Relevant stormwater criteria – compliance with high level municipal and agency documents (i.e. Subwatershed study, master drainage plan).

Site users – who are the users and how will they use the site in future (i.e. are pedestrians using this street to access other services such multi-use pathways, bus routes, commercial areas).

Surrounding land use – schools, community centers, industrial, residential or commercial areas.

Project support – are the local users likely to support the initiatives and become engaged in the project (renters vs. property owners).

Mature vegetation – large trees can be a constraint particularly in municipalities with tree protection bylaws.

Underground and overhead utilities – utility conflicts may eliminate an LID option but there are workaround solutions

Accommodation of surface elements – location, sizing, and spacing of LID practices must consider surface elements such as light standard, transit shelters and fire hydrants. The structural support of these also must be considered, for example a light standard near bioretention may require a deeper base.

Current or future transportation requirements - transportation planning initiatives can be integrate into the ROW retrofit design objectives to facilitate future projects.

Existing aesthetic character of the site – neighborhoods with established gardens, mature trees, and professionally landscaped frontages may be more receptive to a higher landscape aesthetic of vegetated LID practices such as bioretention or bioswales.

Existing maintenance protocols and equipment – how is the ROW currently maintained and can the same techniques be used after the LID practice is constructed.

Impacts to local drinking water wells – consider if threats under Source Water Management Plans have been identified.

Encroachment issues (residents encroaching within the ROW) – including fences, driveways, or other structures

Traffic safety issues – are there reports or records of increased traffic issues. If so consider how the LID practice can be used to address the issues.

Parking availability and access – where parking must be preserved, permeable pavement should be considered, but where parking is underused, then impervious area can be reduced with curb extensions or reduced street width.

Additional benefit opportunities – are there other retrofit opportunities that can be incorporated into the retrofit such as park improvements, trail connections and educational signage potential.

Existing municipal policies and by-laws – The existing policies and by-laws review should not be considered as barriers to the project, but instead should be considered in the context of points of discussion for the municipal project team during the implementation process. Undertaken in the context of a demonstration project, the existing by-laws and standards can be relaxed and reviewed within a controlled environment. With all the departments leads present, a demonstration project can be an opportune time to discuss and re-evaluate. Typical municipal codes, standards and bylaws to be investigated may include:

• Noxious weed by-laws – can exclude native species and limit plant selection. Redefinition and re-evaluation of plants within these lists may be warranted.
• Property standards by-laws – can prevent implementation of LID practices such as permeable pavements (gravel or turf stone driveways), bioretention or bioswales which incorporate temporary surface ponding.
• Boulevard planting by-laws – can prevent implementation of LID practices such as bioswales due to plant type and height restrictions of planting along municipal ROW and boulevards.
• Standing water by-laws – can prevent implementation of LID practices which incorporate temporary surface storage. The definition (or redefinition) of ‘standing water’ to allow for up to 48 hours of ponded water within LID practices may be warranted.

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.

A hard surface area (e.g., road, parking area or rooftop) that prevents or retards the infiltration of water into the soil.

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

Natural vegetation and vegetative technologies in urban settings such as: urban forests; green roofs; green walls; green spaces; rain gardens; bioswales; community gardens; natural and engineered wetlands and stormwater management ponds; and porous pavement systems. These systems are designed to provide multiple benefits, such as moderate temperatures, clean air and water, and improve aesthetics.

Surface runoff from at-grade surfaces, resulting from rain or snowmelt events.

Refers to the conditions in which an organism lives and survives or the conditions in which an organism resides. These conditions can be described as aspects of a “physical”, “social” or an “economic” environment, depending on the perspective perceived by the observer.

Water ponded on the ground surface.

Water ponded on the ground surface.