I drove up Chispa road, what 170 becomes at Ruidosa, probably 15-20 miles -well past the gauging station. It was slow going due to the overgrowth, but the road was in fine shape 10 years ago or so. Very boring, but spooky drive - expect a drug lord at every bend - one way most of the way and few places for vehicles to pass. I believe in the hayday of Pablo Acosta - crossings were used to ferry the cash crops into the states. I bet now days the DHS/CBP keeps a sharp eye on the road with the influx of agents in the Marfa sector - easy to drive across the river at several points. No doubt there are road sensors too. Ran into a hoard of Border Patrol, pre DHS/CBP, going up Pinto Canyon road to Marfa. BTW - I certainly wouldn't expect any cell service out that way if you get stuck or have a couple of flat tires...

Many good links out there with information if you do a search for Chispa road texas
Some good pics of the area @
http://tinyurl.com/shanea011 - neat PVC shelter they setup.