I agree. In my local area, Oceanside/Carlsbad CA, urbanization makes for some really fragmented Rail to Trail projects with no-win transitions. One segment that would make sense for a Rail to Trail project near here is from Oceanside Harbor to Las Pulgas Rd in Camp Pendleton. Currently there are only two options. One is to ride the shoulder of Interstate 5, or go through the Camp Pendleton Marine Base via Stuart Mesa Rd. I take Stuart Mesa. The freeway is popular only with those who refuse to wear helmets, which are manditory on base.

There is a rail line from LA to San Diego, that I actually ride daily to work, that follows really close to the freeway. This old truss bridge, http://goo.gl/maps/uxu58 , is currently being replaced with a concrete bridge adjacent. Converting it to a bike bridge is something I would like to see, rather than tearing it down. (I can get pretty nostalgic. I grew up with it)