A Roman “dual carriageway” has been unearthed by archaeologists along with the remains of an ancient British boom town.

Excavation work for HS2 has uncovered the remains of a 26-acre settlement near Chipping Warden in Northamptonshire, which reveals signs of entrepreneurial town planning in Britain more than 1,700 years ago.

Archaeologists have discovered a “dual carriageway” twice the side of an ordinary Roman road running through the site, likely laid to ease congestion for merchants and their carts cramming into what was a thriving trading town.

Its oversized infrastructure shows the commercial importance of the site, which enjoyed a boom in the third century AD, experts have said, and finery from across the Roman Empire poured into the town before it went bust with the end of Roman rule.

James West, the site manager, said that the well-preserved Roman “dual carriageway” once helped make the settlement a “market hub”, adding: “Most Roman roads we find are about four metres [13ft] across, but this is 10 metres [33ft].

“We think the reason for that is to allow two streams of traffic to pass through this area. This would have been a very busy area at that time, and you can imagine people loading and unloading goods when they arrived here.”