It runs 5.5 km east , under Sheppard Avenue from Sheppard station on the Yonge line ( now called Sheppard-Yonge ) , to Don Mills station at Sheppard and Don Mills Road . It runs 5.5 k east , underneath Sheppard Avenue from Sheppard station on the Yonge line ( now renamed Sheppard-Yonge ) , to Don Mills station at Sheppard and Don Mills Road .