Complex sentence: The main northbound exit to Hay Street is via an access road, beginning from the Mounts Bay Road exit ramp, that rejoins the freeway as an outside lane on the shared Riverside Drive and Mounts Bay Road entrance ramp.
Split into simpler sentences: The main northbound exit to Hay Street is via an access road, which begins on the Mounts Bay Road exit ramp. The access road rejoins the freeway as an outside lane on the shared Riverside Drive and Mounts Bay Road entrance ramp.