Md. Code, Transportation § 21–1412

(a) Except at the direction of authorized personnel, vehicular traffic may not cross the double white lines that designate the vehicular traffic lanes in a tunnel.

(b) Except at the direction of authorized personnel, trucks and slow moving vehicles may be driven only in the right lane of a tunnel.

(c) The driver of a vehicle may not sound his horn or flash his headlights in a tunnel.

(d) While in a tunnel, a person may not use any cutout or other device that allows exhaust gases to escape a motor without passing through a muffler or silencer.