What is the test for failing to give way to an ambulance, police or fire department vehicle?

5 23 V.S.A. 1033, in relevant part, provides:

"Except as hereinafter provided, all vehicles shall give the right of way to other vehicles approaching at intersecting highways from the right; and shall have the right of way over those approaching from the left; provided that upon the approach of an ambulance, police or fire department vehicle which is sounding a siren or displaying a red light or both, all other vehicles shall pull to the right of the lane of traffic and come to a complete stop until such emergency vehicle has passed. . . ."

Violation of this statute under Vermont law constitutes prima facie evidence of negligence. Dashnow v. Myers, 121 Vt. 273, 155 A.2d 859 (1959).