A-road
A412 traffic and collisions
The A412 is an A-road of 20.1 miles, from Hertfordshire to Slough. This page covers its traffic at 15 DfT count points since 2000 and the collisions police recorded on it.
- Traffic in 2025 126m vehicle miles
- Average daily traffic 17,120 vehicles a day, both directions
- Busiest section 26,101 M40 Junction 1 to M40
- HGV share 2.9% of vehicle miles
- Traffic since 2019 −6.5% same count points
- Collisions, 2021 to 2025 255 41.7 per 100m vehicle miles
How busy is the A412?
On an average day in 2025, 17,120 vehicles passed each point on the A412, counting both directions. The busiest section is M40 Junction 1 to M40 (Buckinghamshire), with 26,101 a day; the quietest listed is A412 split to A40, with 8,147.
Busiest sections, 2025
M40 Junction 1 to M40 carries 1.5 times the road’s average flow.
| Section | Vehicles a day |
|---|---|
| M40 Junction 1 to M40 Buckinghamshire · 2.4 mi · HGVs 4.3% | 26,101 |
| A4007 roundabout to A4 Buckinghamshire, Slough · 3.2 mi · HGVs 2.6% | 20,587 |
| A41(T) to A411 Hertfordshire · 1.6 mi · HGVs 0.8% | 19,555 |
| A4178 to A404 Hertfordshire · 3.5 mi · HGVs 0.9% | 18,265 |
| B376 to A332 Slough · 0.5 mi · HGVs 0.7% | 17,019 |
| A404 to Long Lane Hertfordshire · 1.2 mi · HGVs 1.1% | 15,302 |
| A405(T) to A41(T) Hertfordshire · 0.9 mi · HGVs 2.5% | 14,588 |
| A4 to B376 Slough · 0.6 mi · HGVs 1.6% | 12,345 |
| A412 split to A40 Hertfordshire, Buckinghamshire · 4.5 mi · HGVs 8.3% | 8,147 |
Source:DfT,UK Motoring analysis 2000 to 2025 Updated
Route
Hertfordshire to Slough · 20.1 miles
A412 traffic and collisions by section
12 sections between junctions, in route order. Each is the average of its DfT count points, weighted by length. 1 short link roads and spurs (0.9 miles) count in the road’s totals but are not listed.
Sections Tap a column heading to sort
| # | |||
|---|---|---|---|
| 1 | A405(T) to A41(T)Hertfordshire | 14,588 | 12 |
| 2 | A41(T) to A411Hertfordshire | 19,555 | 65 |
| 3 | A411 to A4178Hertfordshire | 37,140 | 7 |
| 4 | A4178 to A404Hertfordshire | 18,265 | 37 |
| 5 | A404 Riverside Drive to A404 Chorleywoood RdHertfordshire | 23,289 | fewer than 3 |
| 6 | A404 to Long LaneHertfordshire | 15,302 | 11 |
| 7 | Long Lane to A412 Denham WayHertfordshire | 13,924 | fewer than 3 |
| 8 | A412 split to A40Hertfordshire, Buckinghamshire | 8,147 | 20 |
| 9 | M40 Junction 1 to M40Buckinghamshire | 26,101 | 19 |
| 10 | A4007 roundabout to A4Buckinghamshire, Slough | 20,587 | 50 |
| 11 | A4 to B376Slough | 12,345 | 12 |
| 12 | B376 to A332Slough | 17,019 | 15 |
Vehicles a day is the average daily flow in 2025. “Since 2019” compares the same count points. Collisions are those with the A412 as the first road, placed on the nearest section by their recorded position; rates (per 100 million vehicle miles) are shown for sections of half a mile or more with 10 or more.
A412 traffic by vehicle type
Cars and taxis make up 80.5% of the vehicle miles on the A412. HGVs account for 2.9%, rising to 8.3% on A412 split to A40.
Vehicle mix, 2025
Source:DfT,UK Motoring analysis 2000 to 2025 Updated
HGV share of traffic
| Year | HGV share |
|---|---|
| 2000 | 3.4% |
| 2001 | 3.0% |
| 2002 | 3.3% |
| 2003 | 3.4% |
| 2004 | 3.6% |
| 2005 | 3.3% |
| 2006 | 3.1% |
| 2007 | 3.1% |
| 2008 | 3.0% |
| 2009 | 2.7% |
| 2010 | 2.7% |
| 2011 | 2.7% |
| 2012 | 2.7% |
| 2013 | 2.6% |
| 2014 | 2.6% |
| 2015 | 2.6% |
| 2016 | 2.7% |
| 2017 | 3.0% |
| 2018 | 3.0% |
| 2019 | 3.0% |
| 2020 | 4.1% |
| 2021 | 4.0% |
| 2022 | 3.9% |
| 2023 | 3.7% |
| 2024 | 2.9% |
| 2025 | 2.9% |
Source:DfT,UK Motoring analysis 2000 to 2025 Updated
A412 traffic trend
Traffic on the A412 came to 126 million vehicle miles in 2025. At the count points present in both years, it is down 6.5% on 2019, before the pandemic, and down 13.3% on 2015.
Vehicle miles a year
Like for like, traffic is down 15.5% on 2000.
| Year | Vehicle miles |
|---|---|
| 2000 | 139m |
| 2001 | 149m |
| 2002 | 146m |
| 2003 | 140m |
| 2004 | 143m |
| 2005 | 135m |
| 2006 | 139m |
| 2007 | 135m |
| 2008 | 134m |
| 2009 | 130m |
| 2010 | 129m |
| 2011 | 133m |
| 2012 | 138m |
| 2013 | 133m |
| 2014 | 136m |
| 2015 | 138m |
| 2016 | 138m |
| 2017 | 131m |
| 2018 | 132m |
| 2019 | 133m |
| 2020 | 104m |
| 2021 | 115m |
| 2022 | 123m |
| 2023 | 125m |
| 2024 | 124m |
| 2025 | 126m |
Source:DfT,UK Motoring analysis 2000 to 2025 Updated
Average daily flow
| Year | Vehicles a day |
|---|---|
| 2000 | 20,186 |
| 2001 | 21,635 |
| 2002 | 20,772 |
| 2003 | 19,967 |
| 2004 | 20,364 |
| 2005 | 19,310 |
| 2006 | 19,835 |
| 2007 | 19,258 |
| 2008 | 19,098 |
| 2009 | 18,484 |
| 2010 | 18,331 |
| 2011 | 18,946 |
| 2012 | 19,733 |
| 2013 | 19,027 |
| 2014 | 19,400 |
| 2015 | 19,651 |
| 2016 | 19,703 |
| 2017 | 18,705 |
| 2018 | 18,195 |
| 2019 | 18,308 |
| 2020 | 14,284 |
| 2021 | 15,780 |
| 2022 | 16,910 |
| 2023 | 17,220 |
| 2024 | 17,074 |
| 2025 | 17,120 |
Source:DfT,UK Motoring analysis 2000 to 2025 Updated
The chart counts the whole road as it was each year, so new or renumbered stretches move it. The percentage changes compare only count points present in both years. In 2025, 1 of the 15 count points were counted; DfT estimated the rest from earlier counts and local trends.
A412 collisions
Police recorded 255 collisions with the A412 as the first road from 2021 to 2025, 55 of them fatal or serious. That is 41.7 per 100 million vehicle miles, higher than the 31.5 for all A-roads in Great Britain. On average there were 2.5 a year for each mile of road.
Reported collisions by year
Down 5.9% from 2021 to 2025.
| Year | Slight | Fatal or serious |
|---|---|---|
| 2021 | 35 | 16 |
| 2022 | 39 | 11 |
| 2023 | 45 | 11 |
| 2024 | 42 | 8 |
| 2025 | 39 | 9 |
Source:DfT STATS19,UK Motoring analysis 2021 to 2025 Updated
Sections with the highest collision rates
Per 100 million vehicle miles, 2021 to 2025. Sections of half a mile or more with 10 or more collisions.
| Section | Per 100m vehicle miles |
|---|---|
| A41(T) to A411 Hertfordshire · 65 collisions | 116.0 |
| B376 to A332 Slough · 15 collisions | 99.7 |
| A4 to B376 Slough · 12 collisions | 91.6 |
| A405(T) to A41(T) Hertfordshire · 12 collisions | 51.7 |
| A4007 roundabout to A4 Buckinghamshire, Slough · 50 collisions | 42.6 |
| A4178 to A404 Hertfordshire · 37 collisions | 32.7 |
| A404 to Long Lane Hertfordshire · 11 collisions | 31.6 |
| A412 split to A40 Hertfordshire, Buckinghamshire · 20 collisions | 31.1 |
Source:DfT STATS19,UK Motoring analysis 2021 to 2025 Updated
A further 47 collisions were recorded at junctions where the A412 was the second road; they are not in the figures above. Fatal or serious uses DfT’s adjusted serious figures. How we count collisions
Council areas on the A412
In route order. Each is the highway authority DfT files the count points under.
- Hertfordshire
- Buckinghamshire
- Slough
Data sources and methodology
| Figures | Source | Period | Records | Updated |
|---|---|---|---|---|
| Traffic counts and vehicle mix | Road traffic statistics (AADF by count point) Department for Transport Derived statistics UK Motoring | 2000 to 2025 | 15 count points in 2025 | 15 September 2026 |
| Reported collisions | Road safety open data (STATS19) Department for Transport Derived statistics UK Motoring | 2021 to 2025 | 255 reported collisions | 15 September 2026 |
- Annual average daily flow (AADF) is the average number of vehicles passing a point on a typical day of the year, both directions combined.
- Vehicle miles are AADF multiplied by link length and 365, summed over every count point link on the road.
- Sections join count point links between junctions, using the link lines in DfT’s major road database.
- STATS19 covers personal injury collisions reported to the police. Damage-only collisions are not included, and not every injury collision is reported.
- Serious and slight figures are DfT’s adjusted estimates, which allow for police forces moving to injury-based reporting.
- Counts of one or two collisions below Great Britain level are shown as “fewer than 3”.
Contains public sector information licensed under the Open Government Licence v3.0.