The road would relieve Magdalene Street, Bridge Street, Sidney Street and the centre generally - the "spine" from Hills Road to Huntingdon Road (which is essentially one of the Roman roads through Cambridge, with a kink).
Later it was decided to "break the spine" instead of relieving it (the Bridge Street closure being the latest stage in the breaking).
The debate over the Spine Relief Road went on for a quarter of a century between City and County councils and Cambridge University.
This plan now seems quite radical (and it's inconceivable anyone would seriously suggest it now), however it wasn't much more radical than the plan which went ahead for Elizabeth Way and Bridge, in the early 1970s.
See also the Lion Yard and Petty Cury development.