It is usually safe. It is usually safe to take a 5-6 hour road trip at 29 weeks if a woman has no preterm contractions or other risk factors for premature delivery. Bouncing on the highway causes problems for some women. In the car, do the "soleus pump", which is essentially moving one's foot up and down in order to increase blood flow and prevent clotting. One should also get out and walk around every hour or so.
Yes. As long as you dont have any recent unusual cramps or contractions, pain etc. When you are travelling, especially for severla hours it is advisable to make frequent stops to stretch and hydrate yourself well, to avoid any clot in the legs.