Posted by: wesleyjohnston | July 23, 2012

Northern Ireland’s busiest road is, er…

The DRD was recently asked by MLA Peter Weir to list the traffic volumes on the top fifty busiest roads in Northern Ireland. Their answer, given by Roads Service, is given on pages 187-190 of this PDF file. The figures all relate to 2009.

Top of the list is: A12 Westlink with 80,980 vehicles per day in 2009.

No! Horror! – surely not Roads Service, of all people, perpetuating the myth that Westlink is Northern Ireland’s busiest road! This is one “fact” that gets reported routinely in the media, but it’s simply not true. To be fair, Roads Service qualify their answer by saying that these figures are of “routes, or links along a route”, but that’s not the question that Mr Weir asked, nor is it a distinction likely to be caught by someone hearing these stats on the hoof.

So let’s unpack these figures.

To begin with, let’s look down the list to the road ranked number 7. It’s M2 “Fortwilliam Interchange – Inbound”, with 48,950 vehicles. Number 8 is “M2 Fortwilliam Interchange – Outbound” with 48,460. In other words, roads 7 and 8 are actually the SAME ROAD, but measured one-way in each case. Adding these together gives you the actual traffic level on the M2 foreshore at Fortwilliam, which turns out to be 97,510 vehicles, easily muscling the Westlink out of its supposed number 1 place.

That’s not all. These figures are based purely on Roads Service’s statistics – and these are based solely on their traffic census points, of which there are 330 in the province. This means that any road that is busy, but doesn’t have a census point, is not listed. In most cases, this does not really matter. However there is one major road that, inexplicably, does not have a census point despite being incredibly busy.

Which one, I hear you ask? The M3 motorway, which at its widest point over the Lagan Bridge is an impressive 8 lanes wide. Hardly one to casually skip over. It’s not listed in Roads Service’s answer because it has not been measured. Fortunately, however, we have information dating from 2004 when traffic levels on the M3 were measured as part of the study into the proposed York Street interchange upgrade. These showed 90,900 vehicles using the M3 Lagan Bridge daily. Given that traffic levels have barely changed since 2004 (yep, it’s true, although you don’t hear it much) this figure is probably still accurate for 2009.

This beats the Westlink down into third place. Oh dear.

And yet there is more! Roads Service’s census point on the M2 is under Fortwilliam roundabout, so it doesn’t include any traffic entering and leaving the motorway there. What about all the vehicles on the M2 between Fortwilliam and York Street? Loads of them must surely exit or join at Fortwilliam. So this census point actually under-estimates the traffic levels on the M2 foreshore. The busiest stretch is clearly between Fortwilliam and Duncrue Street, where a good percentage of traffic leaves the M2. Taking into account the traffic that exits/joins at all these junctions (based on the aforementioned 2004 York Street report), the traffic level on the M2 here is actually closer to 126,400 vehicles per day!

We also don’t have figures for the stretch of the M2 between junctions 1 and 2, i.e. Fortwilliam and Greencastle. Unfortunately there are no combinations of statistics that can allow us to work this out, except that it must at the very least, be all the traffic measured passing under the Fortwilliam roundabout. So the lower limit for the M2 between j1 and j2 is 97,410 vehicles, and almost certainly more. This beats the Westlink down to fourth place.

Don’t leave yet – there is still more! Roads Service data shows that the traffic figure on the first stretch of the M1 (Broadway to Saintfield Road) is 74,250 vehicles per day, and the third stretch from Black’s Road to Saintfield Road Lisburn is 51,850 per day. There is no counter on the second stretch from Stockman’s Lane to Black’s Road. But the amount of traffic here must surely lie somewhere between these two figures, right?

Wrong, as it turns out. Roads Service have traffic counters on the off slip and on slip at Black’s Road. Since this is a limited access junction, the traffic levels between Stockman’s Lane and Black’s Road MUST be the figure from Black’s Road to Saintfield Road Lisburn PLUS the Black’s Road onslip PLUS the Black’s Road offslip, which turns out to be 85,960 vehicles. This makes the Stockman’s Lane to Black’s Road section of the M1 busier than the Westlink, and indeed busier than the section of the M1 approaching Broadway. Oh dear, the Westlink drops to fifth place….

So I offer here, for Peter Weir and everyone else, my own list of the top ten* busiest roads in Northern Ireland in 2009:

  1. M2 (Fortwilliam-Duncrue Street) – 126,400 per day
  2. M2 (Greencastle-Fortwilliam) – at least 97,410 per day
  3. M3 Lagan Bridge – 90,900 per day
  4. M1 (Stockman’s Lane-Black’s Road) – 85,960 per day
  5. A12 Westlink (at Roden Street) – 80,980 per day
  6. M1 (Broadway-Stockman’s Lane) – 74,250 per day
  7. M2 (Greencastle-Sandyknowes) – 64,010 per day
  8. A2 Sydenham Bypass (at City Airport) – 58,270 per day
  9. M1 (Black’s Road-Saintfield Road) – 51,850 per day
  10. A2 Holywood Bypass (at Palace Barracks) 45,100 per day

Note: The traffic level given for Westlink is at Roden Street, its busiest section. We can derive two other figures by adding together figures from different census points. Thus the A12 Westlink between Clifton Street and Divis Street carries 76,280 vehicles per day. And the stretch from Clifton Street to York Street carries 73,690. It’s a grey area as to whether these figures should be inserted in the above list, so I’ll leave it up to you to decide!

*Fifty was just a bit more work than time allows!

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Responses

  1. I hope you have shared this with Mr Weir

    Editor: Yes, via Twitter!


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