Imagine the surprise of the motorist at a collision I once investigated. He parked at the side of the road, opened his door, and a passing car tried to tear it off! It's a good thing he didn't step out while he opened the door.
What went wrong here? The motorist didn't look first, or didn't see what was overtaking him. He probably felt safe in the fact that he had stopped close to the curb and was out of harm's way.
Failing to look or see when you open your door poses a significant threat to cyclists. They must use the right hand edge of the roadway and are difficult to see because of their size. The cyclist that slams into an opening car door can be seriously injured.
People must not open the door of a motor vehicle on the side available to moving traffic unless and until it is reasonably safe to do so. Once a door on that side is open, it must not be left open for longer than is required to load or unload passengers. One must always look carefully in the rear view mirror for any overtaking traffic before opening that door.
Reference Link: http://www.drivesmartbc.ca/collisions/it-safe-open-your-door