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May 2009
« Apr   Jun »


The Crumbling Streets of Toronto

It is very obvious in the City of Toronto that the streets are falling apart. Streets that are in high demand – Bayview Avenue, Yonge Street, Mt. Pleasant Avenue, etc – are all looking worse-for-wear.

Whether you’re in a car, on foot or on a bicycle you’ll notice the new cracks and potholes of the streets. Back in April I wrote a blog on the increasing number of potholes in the city, why they happen and the cost the city must bear as a result. I rode my bike to work this morning and was just amazed at the number of large cracks in the road, along with the potholes, that made my ride very uncomfortable.

What causes these large cracks in the road?

The engineer in me is about to come out here. The roads in Toronto have been repaired over and over again, so an original paved road that spanned from sidewalk to sidewalk has now been disconnected. You know those sticky, tack like lines on the road that get really soft in the summer, those are either naturally occurring cracks in the road but also a joint between new and old pavements.

It is these ‘joints’ that is causing all the major cracking. These ‘joints’ are a result of the inability of the old and new concrete to bond together. And even though there is this ‘tack’ seal slowly the crack erodes both from cars and from the weather. To make it really simple: the first side of the joint is called the ‘approach’ and as the car drives over the ‘approach’ it sinks away from the ‘leave’ side. This discrepancy between the ‘approach’ and the ‘leave’ causes the tire to slam into the edge of the ‘leave’, breaking away bits of the roads. This picture best describes what happens.

Over time this grows and grows and grows … from what was a small sealed crack to a giant gaping hole.

When does this happen in practice?

This morning I thought to myself I think one of the worst programs the city initiated was replacing all of the sewer grates. The original sewer grates were dangerous to ride over and cyclists complained. The city initiated a program to replace all existing grates. Instead of designing one that fit the original hole the city designed new ones. Although these are safer to ride over the resulting cracks created by the ‘joints’ from the marriage of new and old pavements has actually made this worse. We have replaced one problem with a new one.

In my neighbourhood city workers are also tearing up random transverse strips across roads. Why are they doing this? I’m not quite sure. The strips are usually about two feet wide and can cross anywhere from half a lane to the full width of the road. I’ve seen the construction and it looks like they only tear up the top asphalt and then replace it. And on all the roads I’ve seen it on, it’s not like there are major potholes in the vicinity. This is going to wreak havoc on the roads in the future.

Unfortunately there isn’t much one can do to prevent these cracks. The city really needs to evaluate if the repair they are doing warrants tearing up the street, because it significantly decreases the life of that pavement. These cracks grow from lines in the pavements to gaping holes that could swallow a tire. As budget pressure increases how much money will the city have to spend repairing potholes and cracks?