ranch to market road 620, ranch road 620, or rm 620 is a ranch to market road in the u.s. state of texas maintained by the texas department of transportation (txdot). the road begins at sh 71 in bee cave in travis county west of austin passing along southeastern lake travis, western austin, and several suburban communities west and north of austin before ending at bus. i-35-l in round rock in williamson county. the road has major intersections with i-35, us 183, and sh 45.