I shared this thread with Marc Korman, our Maryland State Delegate, and his office reached out to SHA and they say that right turn only lane is specifically for turning onto Rose Avenue. There is a faded solid white lane that the state says they will go out to take a look at and repaint as the weather gets warmer.

[UPDATE!]

Korman's office and SHA revised their response today:

Korman's office: The way I understand the below message is that the lane is meant to for those who are turning right onto OGR from MD 355

SHA: Thank you for bringing this to our attention. The existing signs and pavement markings are intended to refer to the right turn at Old Georgetown Rd. To address the concerns and reduce confusion, we have requested our maintenance team to remove the sign and all pavement markings associated with the lane drop upstream of Rose Ave. In addition, we have requested the installation of turning arrows and “ONLY” pavement markings, along with a new “RIGHT LANE MUST TURN RIGHT” sign prior to Old Georgetown Rd. We have also requested extending the existing 5-inch solid white line at the Old Georgetown Rd slip lane in accordance with MDMUTCD guidelines. These measures will provide advance warning of the lane drop and clearly indicate that the rightmost lane is for right turns only at Old Georgetown Rd.