The highways specialist will deliver five design and build packages across the A38 corridor under a contract with North Somerset Council.
The wider scheme covers nine locations between Barrow Tanks and the M5 J22 Edithmead Roundabout, aiming to boost journey reliability, safety and active travel links.
Works include new cycle and walking routes, upgraded crossings and junction improvements.
Somerset Council will appoint its own contractor for the four sites south of Sidcot.
A38 Major Road Network Improvement Scheme
Octavius highways operations director Chris Hudson said the firm would work closely with local stakeholders to minimise disruption and maximise community benefits during delivery.
