Heads up on this route. Before setting off on Mex 175 between Oaxaca and Pto Angel ask the local constabularies ( by that I mean the PFP, the Policia Federal Preventiva which are equivalent to the highway patrol, recognizable by the black Dodge Chargers with white doors bearing PFP initials, they should have current info) or truckers coming from the direction you are planning to travel if there are such roadblock protests going on. They may be sporadic, intermittent events.
There is an excellent, albeit somewhat longer, paved alternative if you wish-- take Mex 131 to/from Peurto Escondido ,then just run down the coast on Mex 200 to PA. This excellent and equally curvacious and scenic road joins Mex 175 about 16km south of Oaxaca south of Coyotepec
Depending on where specifically you mean by "around the halfway point" there may also be another escape route back to Mex 131 , but this is a rather long unpaved (?) crossover from Miahuatlan west to San Gabriel Mixtepec. But if you are adventure tourinhg per KLR it may be just your cup of tea.
But ,as you stated , you resolved the problem by simply following oyher traffic on a local detour. This is usually the simlest way.
Last edited by Sjoerd Bakker; 2 Nov 2009 at 22:00.