The city is in the midst of a massive patchwork operation: filling hundreds of thousands of potholes after an especially brutal winter. Here’s a primer on the art of asphalt.
HOW POTHOLES HAPPEN
This winter’s polar vortex has put strain on Toronto’s streets, with the city reporting a 60 per cent jump in potholes since January. In every season, water creeps through small road cracks and is normally absorbed by soil. But when water freezes, it expands and raises the sections of asphalt, leaving them hollow during a thaw. As traffic rolls over the weakened sections, small portions of the road crack and collapse into the hollows.
HOW THE CITY RESPONDS
Step 1: Report
Some city crews attend to potholes reported by 311, while others focus on areas with high traffic or that require frequent roadwork. The city aims to repair holes within five days, though Ontario laws say potholes on major arteries must be repaired within four days, and on expressways like the DVP within two.
Step 2: Fill
A crew of three to four people scoops out any debris and as much liquid as possible before filling the hole with asphalt and smoothing it over. If the hole is dry, a form of bitumen called a tack coat is used to bond old and new asphalt. The city prefers hot asphalt, which is cheaper and lasts longer, but requires an oven to keep it above 85 degrees Celsius. Cold asphalt—commonly used for paving driveways—doesn’t require an oven. It sets over 48 hours as water evaporates.
Step 3: Keep moving
With roughly 35 crews, the city fills between 1,500 and 2,000 potholes a day. (On April 1, they capped 3,070!) The city says some are working 12-hour shifts, and up to 50 crews were dispatched during a January blitz.
WHAT IT COSTS
Each pothole costs about $17 to fix with hot asphalt—which accounts for most repairs—and about $45 with cold. Approximately $2 million of the $3.5 million pothole budget for the 2014 calendar year has been used already. City council passed a motion last week (affectionately named “Potholepalooza”) to tap into $4 million in reserve funds to fill an extra 100,000 potholes. And this isn’t even Toronto’s worst season. In 2009, the city spent a record $6.3 million over the calendar year, to fix 253,409 pits. That fall, federal infrastructure funding helped revamp old, high-traffic streets like Steeles and Yonge. The drop in required repairs led the city to cut its annual pothole budget in half.