A-road
A409 traffic and collisions
The A409 is an A-road of 4.9 miles, from Harrow to Hertfordshire. This page covers its traffic at 5 DfT count points since 2000 and the collisions police recorded on it.
- Traffic in 2025 24m vehicle miles
- Average daily traffic 13,624 vehicles a day, both directions
- Busiest section 17,018 A404 to A4005
- HGV share 1.9% of vehicle miles
- Traffic since 2019 −12.8% same count points
- Collisions, 2021 to 2025 179 150.1 per 100m vehicle miles
How busy is the A409?
On an average day in 2025, 13,624 vehicles passed each point on the A409, counting both directions. The busiest section is A404 to A4005 (Harrow), with 17,018 a day; the quietest listed is A410 to A4140, with 11,292.
Busiest sections, 2025
A404 to A4005 carries 1.2 times the road’s average flow.
| Section | Vehicles a day |
|---|---|
| A404 to A4005 Harrow · 0.5 mi · HGVs 2.1% | 17,018 |
| A4005 to A410 Harrow · 2.0 mi · HGVs 2.1% | 14,895 |
| A4140 to A411 Harrow, Hertfordshire · 0.8 mi · HGVs 1.8% | 12,988 |
| A410 to A4140 Harrow · 1.6 mi · HGVs 1.6% | 11,292 |
Source:DfT,UK Motoring analysis 2000 to 2025 Updated
Route
Harrow to Hertfordshire · 4.9 miles
A409 traffic and collisions by section
4 sections between junctions, in route order. Each is the average of its DfT count points, weighted by length.
Sections Tap a column heading to sort
| # | |||
|---|---|---|---|
| 1 | A404 to A4005Harrow | 17,018 | 39 |
| 2 | A4005 to A410Harrow | 14,895 | 116 |
| 3 | A410 to A4140Harrow | 11,292 | 18 |
| 4 | A4140 to A411Harrow, Hertfordshire | 12,988 | 5 |
Vehicles a day is the average daily flow in 2025. “Since 2019” compares the same count points. Collisions are those with the A409 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.
A409 traffic by vehicle type
Cars and taxis make up 79.6% of the vehicle miles on the A409. HGVs account for 1.9%.
Vehicle mix, 2025
Source:DfT,UK Motoring analysis 2000 to 2025 Updated
HGV share of traffic
| Year | HGV share |
|---|---|
| 2000 | 2.9% |
| 2001 | 3.1% |
| 2002 | 2.9% |
| 2003 | 2.4% |
| 2004 | 2.7% |
| 2005 | 3.6% |
| 2006 | 3.5% |
| 2007 | 2.3% |
| 2008 | 2.3% |
| 2009 | 2.1% |
| 2010 | 2.3% |
| 2011 | 2.2% |
| 2012 | 2.4% |
| 2013 | 2.5% |
| 2014 | 2.3% |
| 2015 | 2.3% |
| 2016 | 2.2% |
| 2017 | 2.1% |
| 2018 | 2.0% |
| 2019 | 1.7% |
| 2020 | 1.9% |
| 2021 | 1.9% |
| 2022 | 1.9% |
| 2023 | 1.9% |
| 2024 | 1.9% |
| 2025 | 1.9% |
Source:DfT,UK Motoring analysis 2000 to 2025 Updated
A409 traffic trend
Traffic on the A409 came to 24.4 million vehicle miles in 2025. At the count points present in both years, it is down 12.8% on 2019, before the pandemic, and down 7.3% on 2015.
Vehicle miles a year
Like for like, traffic is down 15.5% on 2000.
| Year | Vehicle miles |
|---|---|
| 2000 | 29m |
| 2001 | 29m |
| 2002 | 29m |
| 2003 | 29m |
| 2004 | 29m |
| 2005 | 28m |
| 2006 | 29m |
| 2007 | 26m |
| 2008 | 26m |
| 2009 | 25m |
| 2010 | 24m |
| 2011 | 26m |
| 2012 | 26m |
| 2013 | 26m |
| 2014 | 26m |
| 2015 | 26m |
| 2016 | 27m |
| 2017 | 27m |
| 2018 | 27m |
| 2019 | 28m |
| 2020 | 22m |
| 2021 | 23m |
| 2022 | 24m |
| 2023 | 24m |
| 2024 | 25m |
| 2025 | 24m |
Source:DfT,UK Motoring analysis 2000 to 2025 Updated
Average daily flow
| Year | Vehicles a day |
|---|---|
| 2000 | 16,121 |
| 2001 | 16,187 |
| 2002 | 16,213 |
| 2003 | 15,970 |
| 2004 | 16,132 |
| 2005 | 15,769 |
| 2006 | 15,933 |
| 2007 | 14,595 |
| 2008 | 14,281 |
| 2009 | 14,144 |
| 2010 | 13,484 |
| 2011 | 14,788 |
| 2012 | 14,548 |
| 2013 | 14,658 |
| 2014 | 14,702 |
| 2015 | 14,692 |
| 2016 | 15,198 |
| 2017 | 15,151 |
| 2018 | 15,143 |
| 2019 | 15,625 |
| 2020 | 12,110 |
| 2021 | 12,801 |
| 2022 | 13,268 |
| 2023 | 13,152 |
| 2024 | 13,855 |
| 2025 | 13,624 |
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 5 count points were counted; DfT estimated the rest from earlier counts and local trends.
A409 collisions
Police recorded 179 collisions with the A409 as the first road from 2021 to 2025, 31 of them fatal or serious. That is 150.1 per 100 million vehicle miles, higher than the 31.5 for all A-roads in Great Britain. On average there were 7.3 a year for each mile of road.
Reported collisions by year
Down 2.5% from 2021 to 2025.
| Year | Slight | Fatal or serious |
|---|---|---|
| 2021 | 34 | 6 |
| 2022 | 31 | 5 |
| 2023 | 29 | 6 |
| 2024 | 22 | 7 |
| 2025 | 32 | 7 |
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 |
|---|---|
| A404 to A4005 Harrow · 39 collisions | 247.7 |
| A4005 to A410 Harrow · 116 collisions | 223.2 |
| A410 to A4140 Harrow · 18 collisions | 55.3 |
Source:DfT STATS19,UK Motoring analysis 2021 to 2025 Updated
A further 33 collisions were recorded at junctions where the A409 was the second road; they are not in the figures above. Fatal or serious uses DfT’s adjusted serious figures. 99.4% of the collisions could be placed on a section. How we count collisions
Council areas on the A409
In route order. Each is the highway authority DfT files the count points under.
- Harrow
- Hertfordshire
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 | 5 count points in 2025 | 15 September 2026 |
| Reported collisions | Road safety open data (STATS19) Department for Transport Derived statistics UK Motoring | 2021 to 2025 | 179 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.