Md. Code, Transportation § 21–1105

(a) A person may not open the door of a motor vehicle on any side available to moving traffic unless:

(1) It is reasonably safe to do so; and

(2) It can be done without interfering with the movement of other traffic.

(b) A person may not leave a door open on any side of a vehicle available to moving traffic for any period longer than necessary to load or unload passengers.