The excellent 11/09 National Trail write by Joe Bartels correctly describes the current closures of west San Juan Road. Unfortunately this closure prevents access 3 out of 4 weekends to the National/Alta west trailhead at San Juan Point. It would be nice if this information was available on South Mtn Park's web site. Since I'm leading a National Trail hike east to west Dec 19, I went to the park to determine the status of the San Juan Road closures. After a couple of attempts, I finally found a ranger who actually knew something. He claimed the closure was partly due to 'teenage partying' at the west end of the road. I suggested they go patrol the darn thing instead of closing it.
He suggested (as I already plan to do) to instead end my hike north of the Alta trailhead at 43rd and Estrella in Laveen. It's an 'unofficial but approved' trailhead, what ever that means, which adds an additional .4 miles to the hike. You can park along the road there.
When I complained to him that none of the closure info is available on their web site, he said I was preaching to the choir, and the rangers have no input but have to deal with the complaints. I did note the gate at the Summit / San Juan road junction was open for a Red Bull truck, so they could film a commercial. I remember reading a forum post here a while back where a hiker got in trouble for driving past the closed but unlocked gate there, because they were filming a Ford commercial. Money talks, hikers walk, I guess.