M27 road noise: how it affects nearby properties
The M27 is a short but intensely used motorway linking Southampton and Portsmouth along the South Hampshire coast, running through one of the most densely populated non-metropolitan corridors in England. Housing sits close to the carriageway along much of its length, so the M27 generates a high volume of noise enquiries relative to its size.
Traffic on the M27: what the 2025 DfT counts show
The quietest of the M27's 25 count points still records 37,104 vehicles a day, and none falls below ten thousand. Twenty-three exceed fifty thousand and 15 exceed one hundred thousand. The median is 111,100, the lower quartile 75,200 and the upper quartile 126,000, with one point in ten above 126,600 and the highest reading at 146,598. Every figure covers both directions and a full year. For a motorway of about 28 miles, that is a narrow band of heavy use rather than a long tail of quiet stretches, and it fits a corridor running between two large cities.
Along the Hampshire coast the M27 runs from Cadnam, west of Southampton, to Portsmouth, where it carries on as the A27. Measured from the south-eastern end, the first 8 count points centre on about 108,200. The 6 in the middle third are the heaviest, at about 126,600, and include the highest reading of 146,598. The 11 in the western third fall back to about 75,200, though one still reads 136,437. The J5 to J7 section opened on 20 December 1983 and J4 to J5 followed in May 1984, with an £83m overlay of low-noise asphalt on the J5 to J7 concrete begun in March 2024.
At a median of 4.8 per cent, lorries are a small part of the M27 mix, with one point in ten at 7.1 or above, the highest count point at 9.5 and the lowest at 3. The noise here is therefore mostly about the number of vehicles, not the lorry share. A lower share means the heavy, low frequency component is smaller than on freight corridors, though it does not remove it.
| Quarter of points carry under | 75,200 vehicles/day |
|---|---|
| Median point | 111,100 vehicles/day |
| Three-quarters carry under | 126,000 vehicles/day |
| Busiest tenth carry over | 126,600 vehicles/day |
| Busiest single point | 146,598 vehicles/day |
The M27 on the ground
- The M27 runs about 28 miles along the south coast from Cadnam, west of Southampton, to Portsmouth, where it continues as the A27. en.wikipedia.org
- The M27 was built in stages: the J5-J7 section opened on 20 December 1983 and J4-J5 followed in May 1984. ukmotorwayarchive.ciht.org.uk
- J4 to J11 is a roughly 15-mile smart motorway with a permanent fourth lane (hard shoulder kept J7-8) and 23 emergency areas; reopened June 2022. nationalhighways.co.uk
- A £83m scheme that began in March 2024 overlays the concrete between J5 and J7 with low-noise asphalt. portsmouth.co.uk
How loud is the M27, and how fast does it fall away?
Flat coastal ground resembles the open terrain behind the table, so nothing in the landscape does much to interrupt the sound. For a home with nothing screening it from the M27, the median flow of 111,100 vehicles a day gives, reading along the row from 20 m to 200 m, values of 81, 78, 75 and 72 dB. The busier 126,600 flow gives 81, 78, 76 and 73. The two sets sit close together because the typical and busy flows differ by only a modest amount. Inputs: 70 mph and 4.8 per cent lorries. Houses, fences and bunds between a home and the road would change the result.
| Flow | 20 m | 50 m | 100 m | 200 m |
|---|---|---|---|---|
| Typical section (111,100 vehicles/day) | 81 | 78 | 75 | 72 |
| Busiest tenth of sections (126,600+ vehicles/day) | 81 | 78 | 76 | 73 |
Areas near the M27
Passing through: Hampshire.
Communities in Fareham, Portchester, Havant and the newer Whiteley developments border the route closely. The flat coastal terrain offers little natural screening, which increases the relevance of a purpose-designed acoustic barrier — exactly the calculation AcoustaPlot's Barrier Design report provides for a specific garden.
Recent on the M27
Between junctions 4 and 11, through Hampshire, the M27 is a completed “all lane running” smart motorway, with the final variable speed restrictions lifted on 29 June 2022 (the hard shoulder is kept only between junctions 7 and 8).
Source: https://nationalhighways.co.uk/our-roads/south-east/m27-junctions-4-to-11-smart-motorway/
How AcoustaPLOT assesses M27 noise for your property
Coastal flatness makes the M27 a road where buildings and barriers matter more than hills. AcoustaPlot searches its 25 count points for the nearest one up to 8 km away along the motorway, then takes the recorded vehicle numbers and lorry percentage. Distance to the nearest carriageway comes next, followed by ground type, terrain, houses, fences or purpose-built barriers, and any other road or railway. With little natural screening, what stands between home and road is decisive. It reports the day-evening-night (Lden) and night-time (Lnight) levels at your facade, and reads Defra's mapped value for any railway noise where available.
Check my property near the M27 →
M27 noise: common questions
Will the new low-noise asphalt between J5 and J7 lower the levels shown?
An £83m scheme that began in March 2024 overlays the concrete between J5 and J7 with low-noise asphalt. The indicative table is built from flow, speed and lorry share, not surface type, so it will not show the effect of resurfacing. Measured flow remains the starting point, and any change in surface noise would be a separate matter.
What does the permanent fourth lane on the M27 mean for the numbers?
From J4 to J11, roughly 15 miles, the smart motorway has a permanent fourth lane, with the hard shoulder kept between J7 and J8 and 23 emergency areas, and it reopened in June 2022. The counts used here are 2025 measurements of what the road actually carried, taken after that reopening, so they reflect the layout in use.
Could a garden barrier help on the flat Hampshire coast?
Flat coastal ground offers little natural screening, so a well placed barrier can be relevant, but the benefit depends on its height, length, position and the gaps around it. The median here is 111,100 vehicles a day, so the traffic source is substantial. A specific garden needs its own calculation before drawing any conclusion.
How much busier is the M27's busiest section than the rest?
The middle third centres on about 126,600 vehicles a day against about 108,200 in the south-eastern third and about 75,200 in the western third. The single highest count point reads 146,598. The gap between the busiest and quietest thirds is substantial, but every third still sits well above fifty thousand at the median.