The southern end of the M3 runs from Junction 12 at Eastleigh, through Junction 13 at Chilworth, to Junction 14 where the motorway ends at the M27 outside Southampton. This is the busiest part of the M3 by a clear margin.

The busiest stretch of the M3

All three of these stretches are physically counted by the Department for Transport. These are the 2025 figures.

The busiest stretch of the M3

Stretch	Length	Vehicles per day	Lorries	Vans
J11 Compton to J12 Eastleigh	3.5 miles	128,023	9,384	21,473
J12 Eastleigh to J13 Chilworth	1.7 miles	130,785	9,893	21,734
J13 Chilworth to J14 and the M27	1.2 miles	140,750	9,901	23,683

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

The final 1.2 miles into the M27 is the busiest measured stretch of the entire M3 — 140,750 vehicles a day, or about 98 every minute, day and night, averaged across the year.

It is also the most van-heavy part of the motorway: 23,683 LGVs a day, close to one vehicle in six. Add the lorries and better than one in five is a working vehicle.

Traffic builds steadily all the way down: 128,023 at Junction 12, 130,785 at Junction 13, 140,750 at Junction 14. Nothing gets quieter on the approach to Southampton.