Much of Muir Woods Road is now off limits for parking, due to an ordinance passed by county supervisors last week. Typically, as many as 400 cars parked along the road on busy weekends, fomenting concerns about stormwater runoff from vehicles making its way into Redwood Creek. Now just 80 cars can park on specified sections of the road. The new law is the first step in implementing a memorandum of understanding with the National Park Service that supervisors approved this past summer. The park service has not signed the M.O.U., but a park spokesman told the Light that the agreement will likely be finalized by the end of the year. Under the M.O.U., the park will create a reservation system for the monument within two years and all parking along the road will be phased out within seven years. Parking along prohibited sections of road will result in a $99 fine. At last week’s hearing, Doug Karpa, the legal director for the Salmon Protection and Watershed Network, praised the board for taking action, though he added that he hoped the supervisors would fast-track other aspects of the M.O.U. in advance of the current seven-year implementation timeline. A lawyer for the Mount Tam Task Force, a nonprofit that has also been active in pushing for restriction on the road, said that he hoped the group would not need to follow through on a notice of intent to sue sent to the county a few months ago over the environmental impacts. But he noted that would depend on “transparency,” adding that the group was also considering legal action against the park “if that agency doesn’t start, in earnest, to implement the M.O.U.”