Im quite familiar with the route I assume they took: I-5 to Grants Pass OR, 199 to the coast, 101 south to where it meets Hiway 1 near Leggett and heads west to the coast. On 101 south of Crescent City (just south of the Oregon border) theres a stretch that curves through the redwoods high above the ocean. It would have worked well except that stretch of road is somewhat heavily traveled and its very slow (10-40 mph). It would be hard to build up enough speed to catapult off the edge between trees. Its a scary highway IMO and it could have happened there, but highway 1 is a better choice...less traveled, few trees, and they could pick up speed on the the bridge right before they went off the edge. Pretty much the only lighting along these stretches of road is headlights.
So, if this was planned, it was either researched or one of the women had been there before. It is certainly not a day trip even for me in Southern Oregon...probably 7 hours, with long stretches on winding two lane highway. I wonder if they spent the night in Eureka.
Has anyone checked what the weather was like along this route on the Friday they left WA, especially near Westport? Bad weather could make the trip much longer than the estimated 10 hours (Im pretty sure it takes longer than that at best).