If you are like most people you probably haven’t ever considered how to best design a sidewalk; for many people, its as simple as asking, “is there one or not”. But if you are like me, you understand that sidewalk design can play a huge role in the vibrancy of street-level activity, allowing businesses to thrive and acting as the “front steps” to a city.
The design and operation of sidewalks has been an area of interest for me throughout my career. Unfortunately, the design and location of sidewalks, particularly in new subdivisions, is often a decision by a engineering or drafting technologist, based on municipal standards, without consideration of how the sidewalk space will be used.
As a side note, all of the ideas below are intended to apply on streets that should have pedestrian traffic. There are many cases on higher volume roads with heavy distance commuter traffic, where pedestrian access should be limited, or fully separated. But in places where sidewalks work, there are some fairly obvious principles that can make for a great sidewalk, and be used to improve the streetscape.
I’ll use some examples from the town I currently work in to describe how these design principles can work.
This isn’t my first post on sidewalks, I keep coming back…
Pedestrian safety is the primary reason we build sidewalks. The sidewalk should ensure separation from vehicular traffic. There are a couple of ways we can achieve this.
A simple 6″ (150mm) upright or barrier curb provides adequate grade separation for vehicles on slower-speed streets. Vehicles that bump into a curb are directed back onto the roadway. In many places, including suburbs and even downtown areas, roll over (or mountable) curb profile has been installed, which deliberately allows vehicles to mount the curb. This type of curb is not suitable in areas where vehicles travel at higher speeds, or in downtown or urban areas where parked vehicles can easily block sidewalks.
For downtown areas, particularly where on street parking exists, a sidewalk can be placed directly behind upright curb. This allows the sidewalk to be used for both exiting parked vehicles and for pedestrian traffic. For any areas where on street parking turn over is low, the sidewalk should be separated both horizontally and vertically from the roadway.
The ultimate in pedestrian comfort exists where the interactions with roadways are minimized, usually seen in multi-use trails. But some of this comfort can be achieved with the inclusion of horizontal separation. Siting a sidewalk back from a busy roadway, even with a three foot (1 meter) offset or less, can massively improve the pedestrian comfort and safety.
In Revelstoke, we retrofitted a rural cross section with a sidewalk separated with a shallow infiltration swale. What had previously be a challenging, busy road to walk along, is now a preferred route to school for kids.
Fencing or Bollards
Designed specifically to provide a barrier between pedestrians and vehicles and sometimes for security of buildings and public places; fences and bollards are not generally a preferred means of providing safety – it’s more of an indicator of a problem, than truly dealing with the root cause. Interestingly, with a visible physical barrier, vehicular traffic often increases in speed, making pedestrian crossings and intersections more dangerous. Additionally, bollards and fences can be deadly to cyclists if not designed with appropriate offsets and heights.
On-Street Vehicular Parking
A simple ways to improve pedestrian safety is providing on street parking adjacent to the sidewalk. Given enough parked cars, this can provide an intermittent barrier for pedestrians, pushing traffic away from the edge of the street. In areas with higher parking turnover, this can also slow traffic speeds down.
Trees, Streetlights, Bike Racks and Bus Stops
This is kind of a catch-all category for street furniture and facilities, and we’ll discuss these again later. But any object that is placed between the sidewalk and the travelled lanes can provide a safety buffer for pedestrians. Highway design parameters will often include an exclusion zone for obstacles such as these,
designed to provide a safe zone for errors at higher speeds; but on most city streets these parameters should not apply, as the perception of obstacles by drivers often contributes to safer, more aware driving and lower vehicle speeds, leading to increased pedestrian safety.
In recent years, a greater emphasis on comfort and accessibility of sidewalks has emerged through the increased influence of urban planning and legislation such as the American Disability Act requirements. Some of the comfort and accessibility considerations are listed below.
Width, passing space and “sidewalk zones”
One of the main complaints I hear about sidewalk design is that they are not wide enough. When you look at the total right of way width that is used for property access, pedestrian movement, cyclists and vehicular traffic, usually more than half of it is dedicated to automobiles. In Revelstoke, a standard 20m road corridor has a minimum 12m wide roadway (2 x 3.5m driving lanes and 2 x 2.5m parking lanes), with 1.2m sidewalks on one or both sides. While this width may meet some minimum standard, best practice is to consider the use of the streetscape and the needs of the users.
The NACTO Urban Street Design Guide guide provides some design parameters, which are focussed on downtown environments. The big takeaway from this guide is thinking about the sidewalk as having zones across its width:
- Frontage Zone
- Pedestrian Through Zone
- Street Furniture and Curb Zone
- Enhancement and Buffer Zone
The San Francisco Better Street Guide offers other considerations applicable to wider variety of land uses and situations.
I’d recommend a minimum clear sidewalk width of 1.8m in most situations, with specific design requirements to be detailed for intersections, bus stops and high traffic areas.
Grade and the Difference between a “Sidewalk” and a “Ramp”
In many parts of the world, winter conditions set limits on the reasonable sidewalk grade. While roads and streets may be constructed with grades up to a maximum of 12%, this is rarely desirable for sidewalks as traction issues, snow and and ice can have devestating consequences for even the most cautious of pedestrians.
The section header is “comfort and accessibility” of sidewalks, and we really need to consider accessibility standards. While these standards vary by country, region and city, here’s an example design standard:
“When the running slope, or grade, of a sidewalk exceeds 5% it is a ramp. If the sidewalk is adjacent to the street or separated by a narrow planting strip, the sidewalk grade may be equal to the grade of the street and not be considered a ramp.” via MoDOT.
So, for sidewalks adjacent to a street, these are not ramps, and can run with the street, but any other pathways should be designed to a maximum of 5%, with any steeper sections at a maximum of 8.33% with level landings at specific horizontal runs.
Careful consideration should be given for sidewalks in areas where street grades exceed 5%. Providing an age- and accessible- pedestrian-friendly environment will improve walkability and the feel of the community. In areas that frequently deal with snow, traction can become a serious issue at grades greater than 5%, and anything over 10% can be challenging for pushing or pulling a cart or stroller.
Another important aspect, along with the grade, is the crossfall of a sidewalk. Generally, a 1% crossfall is ideal to limit low points and water/ice accumilation, however, a design maximum of 2% crossfall should be attained.
One challenge is managing drivewalk crossings. Driveway crossing let downs should be designed to the municipal standard, however, many driveways standards favour automobile speed and passenger comfort at the neglect of pedetrian comfort and accessibility. Ideally, a 900mm (3′) section of the driveway will remain at a maximum of 2% crossfall. For example, the typical section from Aukland Transportation is shown below, note the right hand side of the design, which maintains the grade to the property line.
Letdowns and Street Crossings
Similar to driveway crossings, is consideration of curb letdowns, these are the parts of the sidewalk at intersections that return you to the street level. One common North American design that I don’t like to see is combining crossing directions into one central letdown right on the corner – this tells me that you really don’t care about pedestrians, but the requirement box has been ticked. Part of the problem is that this type of crossing gives poor directional messaging to drivers, which way is the pedestrian going to go? Maybe they’ll walk diagonally!
For specific design requirements, check local best practice guidelines, but some of the basic considerations when I’ve designed include:
- Avoiding stormwater ponding on sidewalk or in gutter.
- Providing smooth and consistent grade transitions to avoid trip hazards
- Tactile warning surfaces where required
- Location of pedestrian crossing signage and push-buttons
- Protection of pedestrians from turning vehicles
- Adequate, safe turning areas for wheelchairs and strollers.
The preferred material for sidewalks in most parts of the world is concrete. It is long lasting, slip resistant, durable, is easily repaired or replaced in situ, and when constructed correctly, does a good job of resisting cracking and differential settlement. Major tree roots are one of the few issues with improperly considered concrete sidewalks, pushing panels up and creating serious risk.
In our downtown, areas of paving bricks have been used for some sidewalks. I would strongly recommend avoiding these for general sidewalk use due to the maintenance requirements encountered from settlement and trip hazards.
Other materials used include asphalt, gravel, rubber and plastic compounds, and more recently there has been interest in smart surfaces that use solar power, and can change appearance or other modifications as desired. These high tech solutions are unlikely to gain traction outside of specific gimmicky locations due to the cost of installation and maintenance. The other tech solution of interest to me is research into self healing materials, which may reduce ongoing maintenance costs.
What’s a long post without some bonus tips!
We get a lot of snow in Revelstoke, and snow removal from sidewalks is a big deal. For roads with sidewalks and little boulevard space, we generally haul snow away, for areas with no sidewalk, and grassy boulevards, we’ll generally store the snow.
The order of operation is important, getting the snow off the sidewalk onto the road using a sidewalk plow, “just before” a grader windrows the roadway to the centre.
Older sidewalks often suffer from ponding of water, often because surrounding vegetation has grown up around the concrete, or the concrete has sunk. The consideration of where water is coming from and where it is going to is a key part of Civil Engineering, and sidewalk drainage is no exception.
Some options for addressing localized problems are given in this Washington Post Article.
Most municipalities focus street lighting on driver safety and visibility, but there are many situations where lighting up sidewalks is just as important. Downtown areas are often well lit from neighbouring businesses, but there can be areas such as parks, wider road crossings and businesses that are only open during the day, that could benefit from additional lighting for pedestrians.
Some roadside lighting, particularly newer LEDs can be quite directional, with little of the light reaching the sidewalks on either side of the road. In these cases, secondary lighting may be required to provide a feeling of safety.
Leave a comment if you have any other tips for sidewalk design!