Category: Streetscape Planning + Design

About a month ago, I posted a question on my Facebook page which asked,  “What in your view, makes a perfect city street?”  Clearly an unscientific sampling, but I was amazed by the dozens of answers that I received.   They all spoke to characteristics that we can all easily visualize.

Here’s a sampling:

• “ a residential street in Brooklyn Heights. Four story brownstones running down either side of the street and a row of old trees in front of each of them.”
•  “Trees, wide sidewalks, bike lanes, short blocks, lots of pedestrians”
•  “.an unintimidating scale, a few places where people can sit, houses, good sidewalks, street corners that are designed with all different ages and physical capabilities, bikes and motorists accommodated, definitely lots of trees,…”
•  “Wide sidewalks, large tree canopy, outdoor cafes, cleanliness, good people watching!”
•  “No above head wires ,or any wires whatsoever, good evening lighting….treed meridian…..cobble stones….Edinburgh new town crossed with Berlin”
•  “Seating and a boulevard for kiosks and fountains. Go to Lisbon”
•  “….trees, wide sidewalks, seating areas, elegant lighting, no overhead wires, bike lanes…”
•  “ Trees!”
•  “Quality shops . Outdoor cafe seating . Lighting and of course trees”

 There were a few themes common to the posts.   Not one of them mentioned ‘move traffic’ or ‘room for cars’,  though many talked about accommodating both cars and bikes.    Many of them talked about sympathetic architecture and land uses and almost ALL of them spoke to the importance of street trees!  This last point actually surprised me. It is also interesting to note that not one of these comments was from a practitioner.

This little survey got me to thinking.   What IS the perfect city street?   Is there any way to confirm that the design of a new street will meet the goal of a perfect city street?  Is  there any way to confirm that the design of a new street will meet the expectations held by the general public?

Streetscape planning and design is the most complex undertaking in urban design and landscape architecture.  It is so because it requires the successful reconciliation of the widest number of competing interests.   It is the only discipline in design that must successfully marry the following interests:

• Land Use fit (particularly at street level)
• Architectural fit (height, character, animation)
• Right-of-way width, particularly in relation to architectural height
• Day-lighting triangle dimensions and form (triangle vs. rounding)
• Boulevard widths
• Building Set-backs
• Cross-walk design and placement
• Accommodation of dedicated left and right turn lanes
• Median design (where desired)
• Roundabout design (where desired)
• The design of abutting private landscapes
• Transit infrastructure
• Above-ground utilities
• Below-ground utilities
• Vehicular traffic and turning movements
• On-street and adjacent parking
• Bike traffic, comfort and safety
• Pedestrian traffic, movements, comfort and safety
• Street lighting and pedestrian way lighting
• Street tree selection, spacing and sustainability
• Low impact development infrastructure
• Woonerf Design (where desired)
• Street furnishings
• Materials and finishes

It is also the only discipline within urban design where one wrong move by the designer, or domination of the process by one or more interests can compromise the goal of creating a ‘perfect street’.

This is not to suggest that there is one kind of ‘perfect street’, but rather that there are many, and the designers success will be tested by making appropriate decisions given the opportunities and constraints posed by the specific context and street type i.e. local, collector, arterial, retail, residential, mixed use etc.  It will also be determined by the degree to which all vested interests are prepared to compromise (more often than not this is the greatest single challenge).

In addition to this check-list of items to be considered, designers can find their way to a more ‘perfect street’ by reconciling competing interests and adhering to a number of guiding principles:

Ten Principles to Consider in the Design of Perfect Streets

1. The height of buildings which frame the street must be directly proportional to the width of the right of way.   This is to say that a wide street with lower buildings will be infinitely less successful than a wide street framed by taller buildings.   The architecture frames the view of the street and provides a sense of enclosure.  It is therefore critical to its overall success of the street.   This is a law of minimums. (The American Institute of Transportation Engineers “Designing Walkable Thoroughfares:  A Context Sensitive Approach” 2010)

   A generally accepted principle is that one should strive for a minimum ratio of 1:4 building height to ROW width. Preferred ratios can go as high as 1:2 building height to ROW width.  Note that in most city downtown cores the ratio of height to width is MUCH higher.  In these cases, the design of the street and boulevards becomes more important as the building wall can be perceived as overwhelming and therefore the pedestrian experience less inviting.

2. If the street is proposed to have above ground utility poles or already has them…then do all you can to bury them.  This isn’t cheap, but they are an eyesore and upstage everything else that might be good about the street.  They will also limit the degree to which street trees can be used to help frame the street.  Utility companies have spent so much money ‘pruning for clearance’ that they have, in light of shrinking budgets, simply banned the use of large shade trees within their space.
3. If the street is part of a larger community planning initiative, then strive for city blocks no greater than 90-120 metres in length.   This improves both vehicular and pedestrian permeability and allows for more corner land uses and building entrances that help to animate the street.  To the extent possible, make them full turning movement intersections.   This will help to slow traffic and make the intersections more pedestrian friendly
4. The personality of a street will, to a large extent, be expressed as a function of the land uses that frame it.  A residential street will differ in both form and function from a retail/commercial street or a street dominated by office buildings. The land uses will also help to define the way a street will behave and therefore the menu of elements to be employed in its design.
5. Ensure that residential buildings have a minimum 3.0 metre setback to allow for front yard landscaping, steps, fencing at gates etcetera.  On busier streets a wider set-back may be warranted to provide a greater sense of buffering.
6. For higher density residential buildings strive for podiums with a number of individual residential entrances at grade.   Also strive for principle building entrances located at intersections.  This provides direct pedestrian access to transit and other street amenities.
7. If ground floor retail/commercial uses are proposed, then absolutely try to provide on street parking.  This is vital to successful retail and serves the dual purpose of offering pedestrians a sense of protection from traffic.
8. Pay particular attention to the introduction of dedicated right and left turn lanes at intersections.   More often than not, these ‘added lanes’ will be provided at the expense of the boulevards.  As an antidote to this problem, try to widen the right of way at the intersection so that the boulevards and associated streetscapes are not lost.
9. Ironically, the thing that people want most (street trees) is one of the most difficult streetscape elements to provide.   Their long term success and sustainability will be based on numerous constraints including species selection, spacing, soil volume, access to water and drainage, conflicts with below ground utilities, and conflicts with sight lines and driveways.  Try to make street trees one of the first considerations rather than one of the last.
10. Bicycles.  Yes, the one area of continuing and on-going debate among transportation engineers, civil engineers and landscape architects.   I’m not certain the issues will ever be reconciled, but I suggest the following principles apply.   Bicycles are a mode of transportation and so they should share the roadbed with cars and transit rather than the boulevard with pedestrians.    Bike lanes should be grade separated from pedestrian walkways.  They should be a unique colour so as to heighten their profile relative to cars.

There are certainly more principles to be employed in the design of ‘perfect streets’ , but these I think,  represent the major considerations.