Potholes are not random. They are the predictable end state of one process: water getting under asphalt in a climate that freezes. Canada has the cracked roads, the water, and roughly a hundred freeze-thaw flips a year in many cities — which is why we may be the pothole capital of the developed world.
The freeze-thaw cycle, step by step
- Water finds a crack. Rain and meltwater seep through hairline cracks in the asphalt into the gravel base underneath.
- It freezes and expands. Water expands about 9% when it freezes. Under the pavement, that expansion heaves the asphalt upward and hollows out the base.
- It thaws and leaves a void. When the ice melts, the water drains or compresses, leaving a cavity under a thin crust of asphalt.
- Traffic breaks the crust. Every wheel that hits the weakened spot flexes it. Eventually the asphalt shatters into the void — and each passing tire mines the hole bigger.
Why March is the cruelest month
Mid-winter, roads stay frozen solid — hard but stable. The damage explodes when temperatures start crossing 0°C daily: melt by afternoon, freeze by night. A single spring week can cycle a road through a dozen freeze-thaw flips. That’s why city pothole budgets are spent between March and May, and why RoadRot reports spike then too.
Why patches fail
Winter repairs use "cold patch" — asphalt that can be worked below freezing but never fully bonds to the surrounding road. It buys weeks, not years. Permanent repairs need hot-mix asphalt, saw-cut edges, and compaction — and hot-mix plants largely shut down in winter. A pothole reported in January is usually patched twice: once to make it survivable, once to actually fix it.
What reporting actually changes
Cities triage by severity and by how many people are affected. A pothole with one report is a data point; one with fifteen confirmations is a liability the city can no longer say it didn’t know about — which matters legally, because a city’s best defense against damage claims is that it wasn’t notified. Report the ones on your route, and if one has already cost you a tire, read the damage claim guide.