From Roader's Digest: The SABRE Wiki
The Spitfire Bridge carried the A31 (now B3404) Alresford Road over the A33 Winchester Bypass. It was constructed in the immediate prewar period, and opened in 1940 with the rest of the bypass. It was a concrete parabolic arch bridge.
In 1941 a Curtiss Tomahawk flown by George Rogers flew beneath the bridge, but had to take evasive action after meeting an oncoming HGV. The pilot clipped the bridge and lost 3ft of his plane to it, causing him to later crash while landing. He walked away with only minor injuries.
The story soon spread through the local area, but it wasn't clear what plane it was. It was generally assumed that only a Spitfire would attempt to do such a thing, so the name 'Spitfire Bridge' stuck.
In 1983 the bridge was demolished as part of the upgrading of the Winchester Bypass to M3, being replaced by an unimpressive single-span concrete bridge. The cutting it crossed was widened to house the motorway and parallel A272, which was named 'Spitfire Link' in its honour. The junction of Spitfire Link and the modern A31 is known as 'Spitfire Roundabout'.
It wasn't until 1988 when it was accepted that the plane involved wasn't a Spitfire, but by this time the names had stuck.