What is the test for assuming that another driver will not unlawfully or unsafely enter into the lane designated for oncoming traffic?

However, the proposition that a driver is entitled to assume that another driver will not unlawfully or unsafely enter into the lane designated for oncoming traffic must be read in light of the standard of a reasonably prudent driver (Tucker v. Asleson, supra, at paragraphs 31 and 34 (B.C.A.C.)). For example, on a slippery road, a reasonably prudent driver may need to adjust his speed to take account of the possibility of an oncoming vehicle losing control. Application of the Law Excessive Speed