Posted by: wesleyjohnston | December 26, 2013

We’re not travelling further, so why is traffic growing?

The most recent Travel Survey for Northern Ireland was published earlier this month, and it showed some fascinating trends. For example, the remarkable growth in cycling over the past ten years has been documented by NI Greenways. However, in this blog I want to focus more on trends to do with with car drivers and traffic on the roads in general.

What is NOT changing in Northern Ireland:

Firstly, it is worth pointing out some things that, perhaps counter-intuitively, are not changing.

1. People are not travelling any further now than they were ten years ago. Despite fears that we are becoming addicted to travel, and are travelling ever further in our everyday lives, this is not the case in Northern Ireland. In 2002 the average person in Northern Ireland traveled 5887 miles per year, which is virtually unchanged ten years later at 5873 miles per year [1]:

Miles travelled per person per year, Northern Ireland

2. People are not using cars any more now than they were ten years ago. The average person in 2002 was travelling 4819 miles by car per year, which is again virtually unchanged ten years later at 4791 miles by car per year. So the average person is not using cars any more now than they were ten years ago. We are not using our cars more and more every year as is often claimed.

Miles travelled by car per person per year, Northern Ireland

3. People are not spending any longer travelling now than they were ten years ago. The average person in 2002 spent 300 hours travelling per year, which is once again virtually unchanged ten years later at 295 hours travelling per year. Despite fears to the contrary, we are not becoming a society that spends ever longer periods of time travelling. We spend no more time travelling now than we did ten years ago.

Hours spent travelling per person per year, Northern Ireland

4. People are not walking any less now then they were ten years ago. In 2002 the average person walked 145 miles per year. This is virtually unchanged in 2012 at 149 miles per year. This suggests that we’re getting about the same amount of exercise through travel as we did ten years ago. We’re not becoming ever more lazy travellers.

Miles walked per person per year, Northern Ireland

5. Journeys by private motor vehicle are not getting slower. In 2002 the average person using the four main modes of private motor vehicle (cars, motorcycles, commercial vehicles and taxis) travelled 5206 miles per year with a total time of 213 hours. In 2012 the average person travelled 5279 miles per year by private motor vehicle with a total time of 216 hours. So the average speed of travel by motor vehicle in Northern Ireland has actually risen slightly from 16.0 mph in 2002 to 17.7 mph in 2012. Journeys by motor vehicle are not getting slower.

Average speed by motor vehicle, Northern Ireland

6. Most people are satisfied with their experience of the roads. The travel report asks people for their opinion on difficulties like traffic congestion, road works etc. About two-thirds (68%) of people who travel by motor vehicle said that they had “no difficulties” going to or from work in their vehicle. Only 22% said that they experienced problems associated with congestion or road works, while 12% said the cost of fuel was a problem. Those who did not use a private vehicle were even more satisfied, with over three-quarter (78%) saying that they had “no difficulties” getting to or from work by non-private-vehicle forms of transport. Contrary to what is sometimes assumed, we are not a province of angst-ridden drivers who are highly stressed by congestion problems. In fact, the majority of us appear to be happy with the current situation.

So Why is Traffic Rising?

Here is the apparent paradox. Even though we’re not travelling further, not using cars any more, not travelling for longer and not walking any less, traffic levels are increasing. Since 2000, traffic levels in Northern Ireland have gone up by at least 10%. How can this be? Thankfully the travel report provides us with enough information to be able to answer this question.

The travel report includes all modes of land transport, including walking, cycling and public transport. Not all of these contribute to traffic levels. I am (perhaps controversially for any petrolheads!) omitting cyclists from this figure because, at their current numbers, they do not contribute as much to traffic levels as motor vehicles do. So for “traffic” I am including car drivers, motorbikes, goods vehicles [2] and taxis [3]. Unfortunately we cannot count buses, since we don’t know the average number of people on a bus in Northern Ireland [4]. We can also ignore car passengers as there ought not to be any cars out there that have a passenger but no driver!

On this basis, the total distance travelled by motor vehicles across Northern Ireland in 2002 was 5.76 billion miles, compared to 6.95 billion miles in 2012, an increase of 20.7%. This increase can be accounted for by four factors (three positive, one negative) which are, in rank order:

  • 50% – Increasing use of cars which contain only the driver.
  • 40% – Natural population increase.
  • 15% – Increase in the number of goods vehicles on the road.
  • Minus 5% – Decrease in the use of motorcycles and taxis.

Contribution to traffic growth in Northern Ireland, 2002-2012

A. 50% – Increasing Use of Cars Which Contain Only the Driver.

Although we are not using cars any more than we did ten years ago, we are increasingly using cars as the driver. In 2002, 38% of car occupants were passengers. By 2012 this had fallen to 30%. So there are more car drivers and fewer car passengers today than there were ten years ago:

Distance travelled by car as driver and passenger, Northern Ireland

So although the total distance traveled by car has not increased, people who did so as a car passenger ten years ago are more likely to be doing so as a car driver now. This will naturally increase the number of vehicles on the road, since every driver translates into one car on the road. This phenomenon accounts for half the increase in motor vehicle traffic that we have seen on our roads in the past ten years. This relates to car ownership – I will say a bit more on this later.

B. 40% – Natural Population Increase

Northern Ireland’s population is one of the fastest growing in Europe, currently increasing at a rate of about 0.5% per year. In the period 2004-2009 it was even faster, at 0.9% per year. Of large countries in Europe, only the Republic of Ireland, Turkey and Spain are growing faster than Northern Ireland’s population. This means that, even if each individual person is not travelling any further than they did ten years ago, the fact that there are more people each year means that traffic levels will still go up. Between 2002 and 2012 the population of Northern Ireland rose from 1.69 million to 1.81 million, an increase of 124,000 people. This increase in the population accounts for 40% of the increase in motor vehicle traffic on our roads over this time period.

C. 15% – Increase in the Number of Goods Vehicles on our Roads

In the period 2002 to 2012 the amount of miles travelled on our roads by goods vehicles has increased phenomenally, from 541 million miles in 2002 to 773 million miles in 2012, an increase of 40%. This is far greater than the rate of population increase, so must be accounted for by the success of the Northern Ireland economy over the past ten years. 2002 was only four years after the Good Friday Agreement, so may be something to be pleased about. Nevertheless, it has had a significant impact on traffic levels, accounting for 15% of the increase in motor vehicle traffic over the past ten years.

D. 5% – Decrease in the Use of Motorcycles and Taxis

The more astute among you will have noticed that the three factors already mentioned add up to 105%. This is because this final one is a decrease. Motorcycle use in Northern Ireland has plummeted in the past ten years, dropping by over two thirds. Similarly, taxi usage has fallen, by around a quarter, over the same period. Both of these may be due to increased car ownership. These two factors taken together account for a 5% drop in traffic levels on our roads over the past ten years.

More on the Increase in Car Drivers

To come back briefly to the increasing rate of car drivers as opposed to car passengers. This factor accounts for 50% of the increase in traffic on our roads over the past ten years. Over the time period 2002 to 2012:

  • the number of vehicles registered in Northern Ireland has gone up from 794,477 to 1,060,328, an increase of 33%. This must be largely made up of new cars.
  • the number of people with a driving license has gone up from 69% to 75%, suggesting there are more drivers now than there were ten years ago.
  • the number of households with no car has gone down from 27% to 22%, a decrease of almost a fifth. The figure for Belfast, which is traditionally higher than for Northern Ireland as a whole due to there being both higher deprivation and more alternative transport options, decreased from 46% to 44%.

So we can see that there are definitely more people in 2012 who are both able to drive a car, and who actually have a car to drive. This means that there are more car drivers on the road now than ten years ago, corresponding to the increase in traffic levels.

As we have said, the increasing number of people who are using cars as the driver accounts for 50% of the increase in traffic on our roads over the past 20 years. But how were all these people getting around before they were car drivers? Especially given that people don’t seem to be travelling any more now than they did ten years ago, suggesting that owning a car doesn’t necessarily mean you will travel more. This is slightly harder to work out from the traffic figures.

Firstly, almost all of it can be accounted for by the decrease in car passengers over the same period. In other words, most of the people who are now driving cars were apparently previously passengers in cars.

Secondly, public transport usage has fallen over the past ten years. However, a modal shift from public transport to “car driver” can only account for 6% of the increase in car drivers. This is because the total distance traveled by public transport has fallen by 33 million miles per year over that period, while the total distance travelled as a car driver has increased by 600 million miles per year.

Finally, it is possible that any remaining increase can be accounted for by journeys that would not be happening without the car, i.e. the car is giving people the freedom to travel further. However, the fact that the total distance travelled across Northern Ireland by the average person does not appear to be increasing, makes this a somewhat dubious claim. It’s not possible with the figures we have to say much more than that.

So on the whole it appears that what is happening is that as car ownership increases, so are the number of car drivers and hence traffic levels are going up.

Implications for Future Traffic Growth

Transport policy hinges on predictions of what is going to happen in the future. It is reasonable for us to plan for traffic growth because that is what has been consistently happening since the Second World War. We also tend to assume that traffic levels are going to keep growing unless we “do something”. The nature of the “something” is typically what occupies 90% of discussion time about future transport policy.

To this end it is crucial to understand what is – and is not – fuelling traffic growth. What we have seen is:

  1. The idea that people are travelling further and further each year, contributing to ever-increasing congestion, is a fiction. This is not happening. Distance travelled per person is remaining constant.
  2. Natural population increase accounts for about 40% of traffic growth.
  3. The improving business climate of Northern Ireland accounts for about 15% of traffic growth.
  4. Increasing numbers of car drivers accounts for about 50% of traffic growth.

This means that future traffic growth will only occur through three mechanisms:

  1. A further increase in car ownership rates. Since there is a maximum to the number of cars on the road (one per driver) this figure cannot keep increasing indefinitely. If it kept increasing until there were no car passengers, and only car drivers, then the absolute worst-case, maximum growth in traffic that could result is a 38% increase. This is highly unlikely, however, since it would require car ownership rates per household to approach 100%. A more realistic calculation is to extrapolate the current increase ten years into the future. In this scenario, traffic levels as a result of increasing numbers of car drivers could rise by 10%. If, by contrast, the rate of car ownership slows or even stops, then this figure may not increase at all. So we are looking at a total traffic increase in the next ten years of between 0% and 10%.
  2. A further improvement in the Northern Ireland economy. If the Northern Ireland economy grew by the same amount as it has over the past ten years, then traffic levels could increase by a further 3% over the next ten years. If, by contrast, the economy does not improve it may not rise at all. So we are looking at a total traffic increase from goods vehicles in the next ten years of between 0% and 3%.
  3. Further growth in the Northern Ireland population. If the Northern Ireland population continues to grow at the current 0.5% per year, and there is no reason to choose a different figure, then the population increase, and hence the increase in traffic, in ten years will be about 5%.

This means that by 2022, we could expect traffic levels on Northern Ireland’s roads to grow by anywhere between 5% and 18%, which is not an unmanageable increase.

The debate on whether such an increase is a particularly significant issue compared to the other issues Northern Ireland will face in the coming decade is an ongoing one. However, if this increase was deemed to be undesirable, then there are many ways that it could be tackled. It would not simply be a case of tackling the three causes above, since traffic tends to be concentrated in both location and time of day. This is something I hope to tackle in another blog soon!


[1] The 2002 figure is actually a rolling three year average for the period 2000-2002, and the 2012 figure is actually a rolling three year average for the period 2010-2012. I have simplified them to 2002 and 2012 for the sake of readability.

[2] Goods vehicles are in the travel report under the category “other private”. This category includes large vans and lorries (small vans are counted as “cars”). This category also includes land rovers, jeeps, invalid carriages, motorised wheelchairs, caravans, dormobiles and minibuses. However I am assuming that these latter categories make up an insignificant proportion, so that it is safe to regard “other private” as being essentially made up of goods vehicles.

[3] The report specifically excludes bus and taxi drivers, so only counts their passengers. This is the correct approach, as it avoids double-counting the vehicle. It is assumed that each taxi carries, on average, one passenger. Taxi journeys without passengers are likely cancelled out by taxi journeys with more than one passenger.

[4] It is impossible to work out how many buses are represented by the travel statistics, because we only have the total number of bus journeys made, not the number of buses carried on them. Ignoring buses probably does not have a significant impact on the figures since the number of buses as a percentage of all traffic (which is what we’re looking at) is not high, even within cities like Belfast. Ignoring buses probably has the effect of slightly exaggerating the proportion of cars on the road.



  1. It would be interesting to hear your thoughts on how fuel price changes impact on distances travelled by car, particularly in the light of inevitable price increases in the next 10 years.

    • Currently the majority of drivers don’t cite fuel prices as a matter of concern. At the same time, it’s inevitable that it affects the travel decisions of those either on lower incomes or high mileages. The stats don’t allow us to determine whether factors such as these are impacting on travel, only what the overall travel pattern is. We can speculate that it is having a dampening effect on the amount of travel by vehicle. So unless fuel prices stop rising, that effect will probably continue to be the case.

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