At 5 a.m. Friday morning, San Francisco park rangers closed the gate to the Great Highway for what may be the last time. Voters in November approved Proposition K, aimed at transforming two miles of the Great Highway into a park. With the closure of the gates, that park is one step closer to reality.

Those challenging Prop K believe the measure violates state law by permitting an unauthorized roadway closure and for failing to do an environmental impact review.

Opponents of Proposition K, the contentious voter-approved ballot measure to permanently ban cars from a portion of San Francisco’s Upper Great Highway, are pushing back with a lawsuit filed Tuesday alleging that the move is illegal.