The 10cm piece of concrete fell from an overpass in the city’s east end, on Papineau Avenue near Rosemont Boulevard.
A vehicle was passing beneath the overpass when the concrete smashed into its windshield.
Montreal police say a passenger in the car suffered minor injuries to one arm.
Authorities in Quebec have been on the defensive for some time over the state of the city’s aging infrastructure.
The city’s crumbling roads and bridges are becoming a matter of increasing public concern and there is pressure on all levels of government to address their safety.
Late last month, a massive 25 tonne chunk of concrete collapsed from the top of the city’s Ville-Marie expressway and a tunel collapsed. Two bridges into the city require urgent repairs to ensure their safety and two overpasses have collapsed near Montreal in recent years, causing deaths.
This is a timely reminder to city authorities everywhere that they are there to provide basic infrastructure first and expensive monuments to themselves second.