Best route through Plymouth to the Ferry Terminal

Google Maps "Get Directions" shows the route to the Plymouth Ferry terminal fromthe East as leaving the A374 at Breton Street and taking the B3240 via Vauxhall and Notte Streets.  It appears to me the better route would be to stay on the A374 to the large roundabout and then follow Western Approach, turn right into Union St anmd then left into Martin Street.  Has anyone advice to give me on this first use of Plymouth - we went Portsmouth to St Malo on our previous trips?