Toronto police said the dog wandered onto the eastbound lanes of the Gardiner Expressway downtown around 1 p.m. Police responded to reports of a dog in a locked car in the sweltering parking lot of the Loblaws store on Queen's Quay and were attempting to remove it from the car when it escaped.
Initially, it appeared that the dog had been hit by a vehicle on the expressway, although police later said that account was inaccurate.
"According to K9 officer that recovered the dog on the Gardiner, it does not appear that the dog was hit," police said in a tweet.
The dog narrowly avoided getting hit several times and is now safe.
Cherith Walsh was riding on her motorcycle in the area just before the dog got on the Gardiner.
"I was driving by and I saw this big dog in the middle of the road. I saw police officers trying to stop him. My initial reaction was to get off and try to stop him," she told CBC News in an interview.
"But it was too late. He had already gone past and if I had been there two seconds earlier I would have been able to stop him."
Police say they've responded to 152 calls about animals locked in cars in the city this week as temperatures reached as high as the mid-30s.