(a) The driver of a vehicle shall yield the right-of-way to any authorized vehicle or pedestrian actually engaged in work upon a highway within any highway construction or maintenance area indicated by official traffic-control devices.
(b) The driver of a vehicle shall yield the right-of-way to any authorized vehicle obviously and actually engaged in work upon a highway whenever such vehicle displays such flashing lights as may be required or permitted by law or by regulation of the department.
