The A30 runs through many towns and villages, including Staines, Camberley, Basingstoke, Salisbury, Shaftesbury, Sherborne, Yeovil, Honiton, Bodmin and Exeter. Between west London and Basingstoke the A30 has been replaced by the M3 motorway, and the road is no longer trunked here. Between Basingstoke and Honiton the A303 runs parallel to the A30 between five and ten miles to the north, and since 1946 the A303 has been the trunk road and taken the bulk of traffic. The A303 is being upgraded to make it continuous dual carriageway east of Ilminster. West of Ilminster the A358 will be upgraded to the M5 motorway at Taunton. Between Basingstoke and Honiton the A30 remains, for most of the route, a single carriageway carrying only local traffic.
Between Honiton and Exeter, the A30 is dualled. At Exeter the A30 merges with the M5 motorway, which terminates a few miles west splitting into the A38 and A30 westbound. Now the Bodmin to Indian Queens project has been completed, the A30 is virtually entirely dualled between Exeter and the A30/A39 junction at Carland Cross near Truro, apart from a short section across Bodmin Moor. Continuing west, the A30 returns to single-carriageway until one meets the Chiverton Cross roundabout. From here, another substantial dualled section begins, bypassing the Redruth/Camborne area. The A30 returns to single-carriageway west of Camborne and a mid-1980s bypass takes the road around Hayle. Between Hayle and Penzance, the A30 returns to the original route and it passes through several villages. Approaching Penzance, the A30 briefly becomes a dual-carriageway once again, until the 1980s built bypass. Once west of Penzance the A30 becomes much more a rural road running through or past several villages before terminating at Lands End.
There were plans to restore the rest of the St Austell - Indian Queens freight line (currently only going as far up as St Dennis), and direct rail traffic that way, but this plan was dropped.
It has been subject to a long running campaign for expansion. As Goss Moor is a National Nature Reserve it is one of the most highly protected wildlife sites in the UK, and plans for expansion were strongly opposed. In late 2004 a decision was finally reached, and a new dual carriageway now runs around the moor with the existing road converted to a cycle lane. The first four-mile section of the new dual carriageway between Highgate Hill and the new Victoria Interchange opened at midnight on 9/10 May 2007. The former bottleneck of the iron bridge having now been eliminated means that problems with HGV lorries being stuck under the bridge are a thing of the past. The remaining three-mile stretch of new dual carriageway between Victoria Interchange and Innis Downs roundabout opened on 25 June 2007.
The new dual carriageway means that average travel times along this section of the route have reduced significantly. Several petrol stations along the old route have now closed down, and the former route across Goss Moor is now silent once more. The remains of a Stone Age settlement were discovered along the new route during construction.
Two other improvements, Temple to Higher Carblake and Carland Cross to Chiverton Cross, were planned and would have created a continuous dual carriageway from Exeter to Camborne but these plans were shelved in 2006 as they were not considered a regional priority.