After a long road trip my legs get swollen whats wrong?

Prolonged Sitting: can lead to Deep Vein Thrombosis (DVT). This happens more often on long flights where you really cannot move around much but sitting while riding in a car can do the same. Age can be a factor too. The solution is to take short breaks & walk around a few minutes at least every 2-3 hrs on road trips & long flights both. Also, mention it to your MD next visit for more tips.