One vehicle arrives first at an uncontrolled intersection
A crash at an uncontrolled intersection occurs when a vehicle is driving through that intersection and collides with an approaching vehicle that has failed to yield.
In the diagram, Vehicle B has approached an uncontrolled intersection (an intersection without lights or stop signs) and is proceeding on the roadway. Vehicle A then enters the intersection and the two vehicles collide.

Vehicle "A" = 100%
Vehicle "B" = 0%
The rules of the road
A driver proceeding through an uncontrolled intersection must yield to vehicles already in that intersection or approaching it, and proceed only when it is safe to do so.
The Vehicle A driver must yield to existing and approaching traffic at the uncontrolled section and proceed with caution only when it is safe to do so. Therefore, they would be found 100% responsible.
What does it say in the Motor Vehicle Act?
The applicable sections of the Motor Vehicle Act are:
Questions?
If you have questions about your responsibility assessment, please contact your claim representative.
If you wish to dispute the assessment, find out how to file a dispute.