Map of the M3 Motorway Junctions

All 15 junctions on the M3 — J1 to J14, plus J4A between J4 and J5 — from Junction 1 at Sunbury in the north-east to Junction 14 at the M27 outside Southampton. Each one is listed with the road it connects to and the places it serves — so you can pin down exactly where an M3 closure, incident or set of roadworks actually is before you set off.

How much traffic is there between each M3 junction?

These are the Department for Transport’s 2025 figures for every measured stretch of the M3 mainline, in order from Junction 1 down to Junction 14. The final column says whether the figure comes from a physical count or is the Department’s own estimate — we publish both, and we say which is which.

© M3Traffic.co.uk · Statistics from the Department for Transport

The busiest measured stretch of the M3 is the last mile and a bit into the M27, at 140,750 vehicles a day. The quietest is the long run between Junction 9 and Junction 8, at 56,135 — the M3 carries two and a half times more traffic at its Southampton end than it does across the middle of Hampshire.

Where a stretch is split between two count points we show both rather than picking one, because they are genuinely different measurements of different pieces of road.