Parallel Parking and the Impatient Driver

I've noticed recently that often drivers are impatient of people parallel parking and pass them on the left rather than waiting in the right hand lane for the driver to finish parking before moving forward. In the event of a collision who is at fault - the person parallel parking or the person trying to go around the parallel parking car?
This question turned out to be more involved when I corresponded with the person asking it and learned about what had prompted the query. She had found a place to parallel park, stopped in position to back in, signaled, made sure that the vehicle behind had stopped and began to back in. Like most of us, she concentrated on getting into the parking space properly and did not watch to see that the vehicle behind her remained stopped.
This was an important mistake. Somewhere in the parking attempt, the driver behind decided not to wait, pulled forward to pass and a minor collision occurred. Once the reporting was completed and the decisions made, ICBC decided that the driver backing up was at fault for the collision because she lost sight of the other vehicle while she was backing up. The original query was to try and determine if there were rules about passing that the other driver should have followed.
The Motor Vehicle Act does say that the driver passing on the left must do so at a safe distance and must do so safely. Considering only what was explained here, it would appear that this was not followed as the collision occurred. Were the parking driver's backup and signal lamps working? Perhaps the passing driver did not get the information needed to determine what the parking driver was doing.
Did the passing driver sound the horn? If they did and the parking driver heard it, they are required to give way to the right.
Finally, the Motor Vehicle Act rules and how ICBC finds financial fault are two different and not always related areas. As visitors to this site who have read some of the Case Law stories can see, civil liability does not always work out the way we might expect it to.
All things considered, if the passing driver knew what the parking driver was intending, a few seconds of patience here would have avoided the crash.
Reference Link: http://www.drivesmartbc.ca/behaviour/parallel-parking-and-impatient-driver