Complex sentence: Old Street Roundabout is located on the boundary of the London Borough of Hackney and the London Borough of Islington, and is an interchange system at the junction of Old Street and City Road.
Split into simpler sentences: Old Street Roundabout is a roundabout located on the boundary of the London Borough of Hackney and the London Borough of Islington. It is an interchange system at the junction of Old Street and City Road.