You can take the highway the hole length, but you may be stopped by ongoing construction works. I came back from Samana last sunday and there were no works executed, so we could pass without any stop.
Only about 25 km have asphalt, except the open 10 km, thereof some part only partly and some portions only have the first layer of asphalt.
As works go on this may change daily.
About 70 km are without asphalt and partly still levelling works are ongoing.
Lot of dust as you can imagine.
About 5 or 6 bridges are under construction and you have to use small unpaved raods, partly through ricefields, to pass by.
We had a flat tyre on one of our cars (nearly new and in good condition), and there was little traffic.
All in all, I only recommend to go with 4WD cars, not alone, only in daylight and in good weather conditions otherwise you have lot of mud.
Good luck