Anyone traveling more than four hours, whether by air, car, bus, or train, can be at risk for blood clots.
Full article: https://www.cdc.gov/ncbddd/dvt/travel.html
More than 300 million people travel on long-distance flights (generally more than four hours) each year.1 Blood clots also called deep vein thrombosis (DVT), can be a serious risk for some long-distance travelers. Most information about blood clots and long-distance travel comes from information that has been gathered about air travel. However, anyone traveling more than four hours, whether by air, car, bus, or train, can be at risk for blood clots.
Blood clots can form in the deep veins (veins below the surface that are not visible through the skin) of your legs during travel because you are sitting still in a confined space for long periods of time. The longer you are immobile, the greater is your risk of developing a blood clot. Many times the blood clot will dissolve on its own. However, a serious health problem can occur when a part of the blood clot breaks off and travels to the lungs causing a blockage. This is called a pulmonary embolism, and it may be fatal. The good news is there are things you can do to protect your health and reduce your risk of blood clots during a long-distance trip.