Heading westwards from New Street Station, the line runs under Navigation Street and Hill Street before entering the 772-metre Stour Valley Tunnel (1847) which carries it beneath Suffolk Street Queensway, the Alpha Tower and Broad Street.

From Broad Street, the tunnel continues beneath Centenary Square and the International Convention Centre, passing within 30 metres of Symphony Hall whose foundations are mounted on rubber cushions to reduce external vibrations.

From Symphony Hall, the tunnel continues beneath the Birmingham and Fazeley Canal and the National Indoor Arena before the line re-emerges at Vincent Street, next to St Marks Recreation Ground in Ladywood.