That is the best way. Nobody here knows the numbers of the national road system.
However, I think 3 1/2 hours is being very generous.
Let me see.
Airport to Santo Domingo (east side of the river) 30-40 minutes?
Cross Santo Domingo to Duarte Highway- 45 minutes
To entrance to San Francisco- 1 hour
San Francisco to Nagua - 1 hour
Nagua -> Las Terrenas - 1 hour
I'd say 4:30 would be making good time...maybe a little less....depends on how you drive, plus the construction that is going on can cause tie ups.
HB

