a. No motor vehicle shall make a U turn upon any curve, or upon the approach to, or near the crest of a grade, where such motor vehicle cannot be seen by the driver of any other motor vehicle approaching from either direction within five hundred feet. b. No motor vehicle shall make a U turn within a school zone. For the purposes of this subdivision, the term "school zone" shall mean the distance along a highway passing a school building, entrance or exit of a school abutting on the highway for which a school sign (S1-1) has been posted pursuant to this chapter and in compliance with the manual on uniform traffic control devices maintained pursuant to section sixteen hundred eighty of this chapter. * c. No altered motor vehicle commonly referred to as a "stretch limousine" having a seating capacity of ten or more passengers including the driver shall make a U-turn upon any public highway or private road open to public motor vehicle traffic. * NB Effective November 1, 2019