Skip to main content

Sidewalks

The planners out there might get upset to know that an engineer has crashed their party, then again, who knows, maybe they’ll be happy to have me along. Fifty years ago, Jane Jacobs, an activist, critic, author and urbanist,  wrote the seminal book The Death and Life of Great American Cities. This is the first book to be read by the recently formed City Builder Book Club. This week, the focus is on Chapters 8 and 9. I’m sort of reading along with the group, and reading the various blog posts that are popping up across the blogosphere, and like most people who have read some of Jane Jacobs work, I am left wondering where we went wrong as a group of professionals when we let our cities deteriorate. While the book offers disclaimers as to the applicability of her thoughts, it is easy to see the concepts of public spaces, mixed uses, short blocks, and sidewalks working functionally at all scales of cities.

HolmesStreetBadSidewalkMy favourite chapters are those on sidewalks and public spaces. As a walker, (most of us are), I’m passionate about safe walking routes. Some of us walk further than others, on my daily walks I see the regulars, kids going to school, seniors walking their dogs, and other pedestrian commuters. Now, a little off topic, for while I’m still talking about sidewalks, it is less about the social function that Jane Jacobs discusses, and more about it’s functionality. One of the biggest complaints I have in any suburban area is where sidewalks are incomplete, or difficult to navigate. Streetlight poles, power poles, sign poles, traffic light poles, parked cars and hedges narrowing the width of the sidewalk. Driveways, curb letdowns, cracks, heaving concrete, steep edges, making the terrain of the sidewalk less passable.

In the past, we’ve given more and more space to the automobile, with the net effect often being little more than increasing the speed of vehicles on streets. While that’s happened, the pedestrian has been pushed to the very extremities of the right of way, along with the various and sundry poles and signs that litter the urban and suburban realm. For every fixed object or obstruction such as a drop-off (or curb and gutter), the effective width of the sidewalk should be decreased by about 2 feet (0.6m). In designing new road cross sections, every effort should be made to ensure that a function 1.5m wide sidewalk exists – this allows two pedestrians to pass, or one with an umbrella to navigate the obstacles without fear of bumping.

In many cases, reclaiming the sidewalk should take priority over parking or potentially even additional traffic lanes – what good is a street that has a level of service A for vehicles, but F for pedestrians? Making our environments more pedestrian friendly will bring more people onto the streets and hopefully out of their cars.

Some resources:

 

 

 

Mike Thomas

Mike Thomas P.Eng. ENV SP, is the author of UrbanWorkbench.com and Director of Engineering at the City of Revelstoke in the Interior of British Columbia, Canada. If I post something here that you find helpful as you navigate the world of engineering, planning and building communities, that’s wonderful. But when push comes to shove: This is my personal blog. The views expressed on these pages are mine alone and not those of my employer.

8 thoughts on “Sidewalks

  1. Hey Mike,

    I was just talking about sidewalks this morning, and since you are an engineer, maybe you can answer my questions.

    I have long wondered about prefabbing sidewalk slabs with a tongue and groove joint. You would just pack a nice bed for them, and lay them down. Any heaving due to frost or tree roots should be absorbed in the joint. If a root grows really big you could lift up the slab and grind down the root, then lay the slab back. I would imagine they would even be cheaper because so much could be automated in mass production rather than being handmade on the side of the road–we are not building pianos here!

    What do you think?

    1. Hey Ruben, concrete just isn’t strong enough to tongue and groove, or some other friction joint, especially at 100mm thickness. To make it strong enough you’d need to make it thicker or add fibre reinforcement, both o which would add weight and material costs.

      There are tools out there to make repairing and leveling sidewalks easier, but it’s still a labour intensive endeavor. I like the Canadian product – http://slabsetters.com as an easy way to relevel precast slabs, but this might not be feasible on a municipal scale.

  2. Well, the municipal feasibility is what I think needs a good look. And we agree that what is “feasible” now may not be, given budget or fuel constraints in the future.

    So right now a truck comes out with a giant diamond saw. Another truck brings a backhoe with a jackhammer attachment. The sidewalk is cut and rubbleized. Then it is shoveled into a dumptruck and driven somewhere for further crushing to be used as aggregate to make more concrete.

    A different team shows up to re-prepare the bed and build forms. Some days after that is done the concrete truck shows up and the finishing crew comes to level and finish.

    Some days later another crew comes to strip the forms and repair the landscaping.

    All the while there are traffic cones and flashers left on the street, and parking and traffic disruptions. NRCAN studied the cost of traffic disruptions and found a simple detour could cost millions each year in fuel, time and pollution.

    So that requires two major tools, trucks to carry them, a dumptruck and vehicles to transport three or four crews. It is hard to imagine a way to make this less efficient.

    Let’s assume fibre reinforcement for a tongue and groove. One pickup comes with two guys with two lever slab lifters. They move the slab and use some sort of a rototiller/grinder to shave the roots or heaves. I don’t know what that machine would be, but I think it would fit in a pickup. Then they replace the slab and sweep up in time for coffee break. The slab is reused, and should last for decades. One tenth of the transportation, crew and machinery is required and it is done with one-fiftieth of the labour. I think that would not only pay for the fibre reinforcement, we could afford to scatter gold flakes on the surface of our pre-made slabs just to make them sparkle!

    I would love to see someone run the numbers on this. I would love more if we actually did a pilot project and tested it out. And then let’s talk about how we dig up entire roads to access tiny little wires and pipes….

  3. Your points are well taken. The issue may be that a sidewalk built conventionally will last 30 years without any maintenance, but one that is pre-cast may require more regular maintenance, (potentially at a lesser intensity).

    A similar issue arises with brick pavers in commercial areas, although the problem is magnified due to the number of pieces. One brick standing proud can become a major trip hazard, and the ongoing maintenance required to keep the bricks level and weed-free is an important consideration.

    The Federation of Canadian Municipalities produced a number of Best Practice Guides several years ago, including one on sidewalk design, construction and maintenance. There are a number of considerations to be taken into account including the potential for vehicular traffic and proximity to the roadway. FCM Sidewalk Best Practice.

    Perhaps the biggest “benefit” with cast in place concrete is the fact that the surface finish and grade is almost independent of the workmanship in preparation, the machines do the work, and defects usually take years to show up. With pre-cast panels, the bedding has to be laid perfectly to ensure there is no settlement. And really Ruben, would you deny generations of teenagers the opportunity to immortalize their names in freshly poured sidewalk?

  4. Hm. That FCM report is a Best Practice, but Best Practices can still be crappy, they are just the best we have. What would a reinvented sidewalk look like?

    Come on Mike. We’ll make ten squares. We will only need 30 2X4s to build tongue and groove moulds. A yard and a half of fibre-reinforced concrete will be cheap. Lay them down on your next sidewalk reno and we sit back and watch for the next ten years.

    I think the trip hazard will be reduced because the joints will be every metre, instead of every ten cm. And, with a tongue and groove joint they should heave and move somewhat in unison. That will actually be an improvement over the current sidewalk that has to break a hip before it gets patched.

    Here is another idea. Imagine railroad tracks with concrete ties. Now turn it upside down. The slabs are free to shift on some kind of rail or cable, but the flexible cable keeps them from moving too far out of whack from each other. I like the cable idea, that is a good one. You might even be able to lose the fibre.

    I actually think the bedding could be worse on precast slabs of sidewalk size, because the slab is large enough to span imperfections.

    As far as the teenagers, every grad class can come down to the concrete yard and make their mark in the latest batch, then be given a souvenir map of the location of their name.

  5. You know I’m not one to accept the status quo! But even in Australia (!) which is much less under the influence of American construction (go big or go home) practices, the methodology is almost identical. The best practice is based on research. Even companies who market products for landscaping walkways, concrete decking, etc, like Armtec, aren’t selling a pre-cast product as a common sidewalk.

    My guess, is that with correct construction practices, (subgrade prep, control joints, expansion joints, isolating root damage potential), the current method provides the best overall lifecycle cost. Where this fails, is when there is premature damage, maybe due tree tree roots or poor construction practices, or poor planning, (say driveway locations that are not reinforced). Changing the way we repair these issues has been the goal of many companies over the past decade, with solutions ranging from mud-jacking, vacuum-lifting slabs, expansion grout, and grinding raised surfaces.

    Unfortunately, as with just about every discussion about infrastructure, we get to the question of whether we can afford this into the future. Will we have the means to continue to repair or replace failing infrastructure, even at a reduced level of utility? A gravel path provides say 80% of the utility of a concrete sidewalk, but there are obvious tradeoffs. A concrete sidewalk probably costs about five times as much up-front to build, but to maintain the surface safety and quality over it’s lifespan the maintenance cost is probably less, considering dust control, washouts and weeds as a few examples of issues that may arise on a gravel path.

  6. You make great points here, Mike, which I believe should be shared with others. Your expertise on the subject could be better realized on a crowdsourcing platform. Hence, I encourage you to target and locate a current sidewalk or road issue and report it on the newly launched InfraInput (www.infrainput.org), a web and mobile app that welcomes public input to infrastructure issues. With InfraInput, developed by I and a civil engineering graduate student, entries from everyday users and even experts will be better documented and disseminated for the attention of public managers and policymakers. Mike, you will be an invaluable beta user of our system. Join us on the cause to help rebuild America!

Comments are closed.