What Can Cause Swollen Feet And Ankles While Travelling?

i get very swollen feet and ankles and even calves when traveling. i was told it could be my varicose veins causing this and i do have a lot more veins in my right leg which also is the leg that swells up the most. How can i safely go on a 20 hour car trip? We hope to drive straight thru. Do they have specail socks or something that could pulsate my legs like they use in the hospital to keep circulation going?