It was an idyllic scene recreated in any municipal park: couples out for an unhurried walk, children laughing and chasing one another, singles marching at a slightly faster pace while barking into cellphones.

There was one striking difference, however. The foot traffic was straddling all three lanes of the northbound Highway 400 in Toronto this summer, where, on several occasions, thousands of vehicles ground to a halt while emergency crews cleared an accident.

And, while it's understandable, police say the temptation to wander - or worse yet, to try backing down the highway and then reversing up the nearest on-ramp - can turn a troublesome traffic snarl into a much worse situation.

Sergeant Cam Woolley of the Ontario Provincial Police Greater Toronto Region Traffic Support unit said there have been instances where vehicles reversing up on-ramps have collided with oncoming traffic.

Then there are the stranded motorists who left their cars to wander around and locked themselves out, allowed their vehicles to overheat, ran out of gas or were a great distance away from their rides when the roadway suddenly cleared and their vehicles became on-road hazards.

In such instances, traffic tickets have been issued and, in the case of accidents, charges have been laid - particularly when drivers try reversing up on-ramps.

"But people tend to be not very good at backing up. I've investigated accidents where people are backing up a ramp and (other motorists) are coming on. If they hit, the person backing up is at fault. The ticket is minor (compared with) the danger (of a) crash."

When a traffic accident shuts off all lanes, police set up a post below the scene to divert traffic to the nearest exit ramp. They also try to clear at least one lane to allow some traffic movement.

During a recent accident, when all southbound 400 lanes were closed when a tractor-trailer carrying lumber spilled its load across the road, work crews had to exercise caution when moving the vehicle and its load to avoid causing further damage and facing liability costs.

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