From Los Americas take highway 2 West through SDQ to Highway 1, then North on Highway 1 to STI. Since you passed through La Vega on the way from SDQ to STI turn around and drive South on Highway 1.
Drtampa, this is really helpful. Like if the Dr had road signs saying Route 1 North here Route 2 west there...
OP: From SDQ, take the highway "las americas". Keep straight, don't make any turns. Once you get to Santo Domingo, city, you cross the huge bridge called Puente Duarte. Keep straight. After the bridge, there will be the overpass called "Elevado 27 de febrero". Take the overpass. After you get down from overpass, on the first lights, you will see a construction like a pedestrian walkway overhead. Turn right. That is Maximo Gomez. You will see a furniture shop on your right. Keep going straight for 2 blocks. You will see Banco Popular on your right, tall building. At that interesection you will see another pedestrian walkway overhead, turn left. That is Avenida Kennedy.
Keep straight. Use the overpasses "elevados" on Kennedy. Beware the last overpass that you see turning and swinging left - don't take that or you will end up on the Av. Winston Chuchill, well off your way. On that last overpass, keep on the "ground". This intersection, you will see a large shopping mall and Mc Donal's so you won't miss it.
After that, keep straight, and 2 hours later, you will get to Santiago.