On 3 October 2003, the dual carriageway section was extended to the 3-mile (4.8 km) £25m Aston Clinton Bypass, which was originally intended to be built at the same time as the two sections further south.
It enters Buckinghamshire and the district of Aylesbury Vale.
It crosses the Grand Union Canal, and there is a junction with the B489, and finishes at a roundabout, becoming Aston Clinton Road.
The road goes straight through Aylesbury, which is a bottleneck.
It meets the A4157 at a junction as Tring Road, and the next roundabout is near Aylesbury Grammar School and a Tesco.
It meets the A418 ring-road and becomes Exchange Street, then meets the A413 from Wendover at a roundabout and becomes Friarage Road, passing close to a Morrisons and the railway station.
The A418 turns to the left and A41 continues straight ahead to become Gatehouse Road, then at the next roundabout, it leaves to left as Bicester Road near the Applegreen Aylesbury Service Station.
After four roundabouts, it crosses the River Thame.
It then meets a roundabout with access for the new Berryfields development as well as Aylesbury Vale Parkway before passing under a railway line, then through Waddesdon, then passes close to Westcott near the former airfield of RAF Westcott.
At Kingswood, it passes the Crooked Billet (now the "Akeman Inn") and Plough and Anchor (now an Italian restaurant) pubs.
It enters Oxfordshire and the district of Cherwell, and at Blackthorn it crosses the River Ray and meets a low bridge which was originally a 14-foot (4.3 m) limit but due to bridge strikes, the road was lowered and the bridge now has a 15-foot (4.6 m) limit.

Plans for an Aylesbury bypass exist and are well supported locally but no government decision has been made.
On 3 October 2003, the dual carriageway section was extended to the 3-mile (4.8 km) £25m Aston Clinton Bypass, which was originally intended to be built at the same time as the two sections further south. It enters Buckinghamshire and the district of Aylesbury Vale. It crosses the Grand Union Canal, and there is a junction with the B489, and finishes at a roundabout, becoming Aston Clinton Road. The road goes straight through Aylesbury, which is a bottleneck. It meets the A4157 at a junction as Tring Road, and the next roundabout is near Aylesbury Grammar School and a Tesco. It meets the A418 ring-road and becomes Exchange Street, then meets the A413 from Wendover at a roundabout and becomes Friarage Road, passing close to a Morrisons and the railway station. The A418 turns to the left and A41 continues straight ahead to become Gatehouse Road, then at the next roundabout, it leaves to left as Bicester Road near the Applegreen Aylesbury Service Station. After four roundabouts, it crosses the River Thame. It then meets a roundabout with access for the new Berryfields development as well as Aylesbury Vale Parkway before passing under a railway line, then through Waddesdon, then passes close to Westcott near the former airfield of RAF Westcott. At Kingswood, it passes the Crooked Billet (now the "Akeman Inn") and Plough and Anchor (now an Italian restaurant) pubs. It enters Oxfordshire and the district of Cherwell, and at Blackthorn it crosses the River Ray and meets a low bridge which was originally a 14-foot (4.3 m) limit but due to bridge strikes, the road was lowered and the bridge now has a 15-foot (4.6 m) limit.
Plans for an Aylesbury bypass exist and are well supported locally but no government decision has been made.
A41 road