Another flawed congestion report

Every year TomTom produce a report about how much worse congestion is getting in Auckland, and every year the media lap it up – usually without looking at the flawed methodology of the report. So it was the NZ Herald yesterday:

Auckland’s roads are so congested commuters are spending an extra 45 minutes a day – or four working weeks a year – stuck in traffic.

A new report has revealed the country’s congestion is now worse than Hong Kong with the time spent on Auckland’s roads doubling in the space of three years.

TomTom has released the results of its Traffic Index 2017, an annual report about traffic congestion in cities around the world.

Auckland is ranked as the 47th most congested city on the planet, worse than Hong Kong, which has a population of 7.2 million.

Auckland’s level of congestion has risen from 33 per cent of extra travel time in 2015 to 38 per cent in 2016.

Drivers in New Zealand’s biggest city now spend an extra 45 minutes each day stuck in rush hour traffic, the equivalent to 172 hours, or four working weeks in a year.

As we’ve noted quite a few times before, the way in which TomTom derive their congestion “scores” is pretty meaningless because it focuses so much on comparing travel times between peak and off-peak, rather than actually looking at the overall average travel times for different cities.

We’ve unpicked this methodology before, but perhaps the best explanation of how stupid it is comes from Jarrett Walker, looking at “Urban Mobility Report” produced by the Texas Transport Institute using a very similar methodology to the TomTom report:

The technical core of the argument is simple. TTI’s Travel Time Index, one of their more quoted products, is a ratio of peak congested travel times by car against uncongested travel times by car. In other words, travel times are said to be “worse” only if they get much longer in peak commute hours than they are midday.

This ratio inevitably gives “better” scores to cities where normal uncongested travel times are pretty long — in other words, spread-out cities. Here’s the CEOs’ critique of how the TTI compares Charlotte and Chicago:

Now it seems complete nonsense to say that Chicago, with an average travel time of 32.6 minutes has worse congestion than Charlotte, with an average time of 48 minutes – but that’s exactly what’s happening here. Furthermore, the methodology completely ignores how an increasing proportion of trips taken by rapid transit, walking and cycling aren’t affected by congestion. Jarrett Walker again:

The journalistic spin that TTI itself recommends is that non-car modes matter only if they reduce congestion, and that congestion remains the primary measure of urban mobility.

What’s more, TTI’s suggestion that public transit directly reduces congestion is actually quite fraught, and many transit experts, including myself, steer away from it. Transit certainly creates alternatives to congestion for individuals, and the resulting benefit to individuals can be aggregated to describe society-wide improvements in both productive time and personal/family time. But those calculations are much more clear and direct than any “transit benefit to congestion” overall. That’s because newly freed, high demand road space tends to induce new car trips.

Most transit projects are not trying to reduce congestion, or not all by themselves. If congestion reduction is your goal, you need a combination of transit and market-rate “decongestion” pricing for motorists. For most advocates of transit in the context of compact sustainable cities, the goal is not to reduce congestion but to give citizens options to liberate themselves from it.

This is why it’s so important we invest in a greater range of transport options and particularly ones that are able to move a lot of people reliably and not affected by traffic congestion. Sure not everyone can or will want to use them but we’ve seen first hand in Auckland than when offered good options, many will flock to use them.

Perhaps the most useful way of using the TomTom report is not so much comparing across different cities – for the reasons best illustrated above – but more to track the same place over time. In that respect Auckland is seeing a pretty big increase in congestion over the past few years, up from around 100 hours a year to 170 hours a year. This is a pretty sad indictment, given how much focus the government has on reducing congestion and how much money they continue to sink into building more roads.

It will be interesting to see next year’s results and whether completing the Western Ring Route has made things better, or worse.

TomTom congestion report (repost)

This is a repost from 2013 in the issues with the TomTom congestion report of which the latest version has been released today.

TomTom have once again released their meaningless congestion index.

TomTom has announced the results of the TomTom Traffic Index 2013, revealing New Zealanders waste up to 93 hours a year stuck in traffic and that Wellingtonian’s experienced the worst traffic delays during peak hours, spending up to an extra 41 minutes in an hour commute. The Index also revealed that traffic congestion on non-highways is worse than main roads.

The regional results of the Index covers 9 major cities across Australia & New Zealand, with Sydney listed as the most congested city in the region, followed by Auckland and Wellington.

  1. Sydney 34%
  2. Auckland 29%
  3. Wellington 28%
  4. Melbourne 27%
  5. Perth 27%
  6. Christchurch 26%
  7. Adelaide 25%
  8. Brisbane 23%
  9. Canberra 17%

According to the TomTom Traffic Index, Friday morning is the least congested time to commute in New Zealand. The most congested commute was found to be Tuesday morning, and Thursday evening.

There were no cities from our region featured in the top 10 most congested global cities. Auckland, Wellington and Christchurch ranked 22nd, 25th and 42nd respectively in the world’s most congested cities list.

The ranking by overall congestion level in 2013 were:

  1. Moscow 74%
  2. Istanbul 62%
  3. Rio de Janeiro 55%
  4. Mexico City 54%
  5. São Paulo 46%
  6. Palermo 39%
  7. Warsaw 39%
  8. Rome 37%
  9. Los Angeles 36%
  10. Dublin 35%

“The TomTom Traffic Index gives us a great insight into the state of our traffic network. By providing an accurate analysis of traffic flow and guiding traffic away from congested areas, TomTom plays a key role in helping to ease congestion, improving the traffic flow for the cities,” said Phil Allen, TomTom Maps and Traffic Licensing, SE Asia and Oceania.

Here’s Auckland

TomTom Auckland 2014

It’s meaningless for a number of reasons including:

1. It measures the difference in speed between free flow and congested periods. That means cities with lots of all day congestion there isn’t as much of a difference between peak and off peak times and therefore they get recorded as having less congestion.

2. It doesn’t take into account the speeds at which roads most efficiently move traffic – which is not in free flow conditions. This is something picked up on in research conducted for the NZTA by Ian Wallis and Associates

Various definitions of congestion were reviewed and it was found that the concept of congestion is surprisingly ill-defined. A definition commonly used by economists treats all interactions between vehicles as congestion, while a common engineering definition is based on levels of service and recognises congestion only when the road is operating near or in excess of capacity. A definition of congestion based on the road capacity (ie the maximum sustainable flow) was adopted. The costs of congestion on this basis are derived from the difference between the observed travel times and estimated travel times when the road is operating at capacity.

The graph below shows the engineering definition mentioned above.

speed-flow

3. It doesn’t represent all trips on the transport network. We know that even though only about 10% of all trips to work (which excludes trips for education) are made via PT, it still represents a lot of people. For trips to the City Centre more than half of the people arrive by means other than a private vehicle and many of the PT users arrive via the train, ferry or a bus that has travelled along bus lanes. The people on those services or walking/cycling are doing so often completely free of congestion and so their experience isn’t counted.

4. The data only comes from people with a TomTom device and who have obviously had it on. Many people making the same trip on a daily basis or running a regular errand like going to a supermarket are likely to simply leave their GPS systems off. That is likely to distort the overall figures as they may use routes that have less congestion on them than the route the GPS would select.

5. It can disproportionately impact on smaller cities. As an example if you’re in a larger city and have a 45 minute commute however congestion delays you by 30 minutes that equates to a 67% congestion rate however if you are in a smaller city and you’re commute is only 15 minutes and you get delayed by 15 minutes that’s a 100% delay despite the hold up being half of what the bigger city experienced.

It’s starting to get a bit old now however there’s a good piece on the issues with the methodology in this piece from Reuters, some of which is covered above.

Lastly in the email I received about it they also mentioned this

Of the 138 countries surveyed for the Traffic Index, a global average congestion rate of 26% was recorded, placing New Zealand above the average with a rate of 28%. To put things in perspective, Wellington and Auckland even beat out New York City (39th) in the global rankings, a thriving metropolis of 8.4 million.

So we have worse congestion than New York, a city where the majority get around by methods other than a car and who in recent years has been reclaiming road space for pedestrians, cyclists and buses. Perhaps we should do more of that.

Lastly if we really want to move people around then then the Congestion Free Network would allow people to do that completely free of congestion giving some real choice.

CFN 2030A

TomTom latest meaningless congestion report

TomTom have once again released their meaningless congestion index.

TomTom has announced the results of the TomTom Traffic Index 2013, revealing New Zealanders waste up to 93 hours a year stuck in traffic and that Wellingtonian’s experienced the worst traffic delays during peak hours, spending up to an extra 41 minutes in an hour commute. The Index also revealed that traffic congestion on non-highways is worse than main roads.

The regional results of the Index covers 9 major cities across Australia & New Zealand, with Sydney listed as the most congested city in the region, followed by Auckland and Wellington.

  1. Sydney 34%
  2. Auckland 29%
  3. Wellington 28%
  4. Melbourne 27%
  5. Perth 27%
  6. Christchurch 26%
  7. Adelaide 25%
  8. Brisbane 23%
  9. Canberra 17%

According to the TomTom Traffic Index, Friday morning is the least congested time to commute in New Zealand. The most congested commute was found to be Tuesday morning, and Thursday evening.

There were no cities from our region featured in the top 10 most congested global cities. Auckland, Wellington and Christchurch ranked 22nd, 25th and 42nd respectively in the world’s most congested cities list.

The ranking by overall congestion level in 2013 were:

  1. Moscow 74%
  2. Istanbul 62%
  3. Rio de Janeiro 55%
  4. Mexico City 54%
  5. São Paulo 46%
  6. Palermo 39%
  7. Warsaw 39%
  8. Rome 37%
  9. Los Angeles 36%
  10. Dublin 35%

“The TomTom Traffic Index gives us a great insight into the state of our traffic network. By providing an accurate analysis of traffic flow and guiding traffic away from congested areas, TomTom plays a key role in helping to ease congestion, improving the traffic flow for the cities,” said Phil Allen, TomTom Maps and Traffic Licensing, SE Asia and Oceania.

Here’s Auckland

TomTom Auckland 2014

It’s meaningless for a number of reasons including:

1. It measures the difference in speed between free flow and congested periods. That means cities with lots of all day congestion there isn’t as much of a difference between peak and off peak times and therefore they get recorded as having less congestion.

2. It doesn’t take into account the speeds at which roads most efficiently move traffic – which is not in free flow conditions. This is something picked up on in research conducted for the NZTA by Ian Wallis and Associates

Various definitions of congestion were reviewed and it was found that the concept of congestion is surprisingly ill-defined. A definition commonly used by economists treats all interactions between vehicles as congestion, while a common engineering definition is based on levels of service and recognises congestion only when the road is operating near or in excess of capacity. A definition of congestion based on the road capacity (ie the maximum sustainable flow) was adopted. The costs of congestion on this basis are derived from the difference between the observed travel times and estimated travel times when the road is operating at capacity.

The graph below shows the engineering definition mentioned above.

speed-flow

3. It doesn’t represent all trips on the transport network. We know that even though only about 10% of all trips to work (which excludes trips for education) are made via PT, it still represents a lot of people. For trips to the City Centre more than half of the people arrive by means other than a private vehicle and many of the PT users arrive via the train, ferry or a bus that has travelled along bus lanes. The people on those services or walking/cycling are doing so often completely free of congestion and so their experience isn’t counted.

4. The data only comes from people with a TomTom device and who have obviously had it on. Many people making the same trip on a daily basis or running a regular errand like going to a supermarket are likely to simply leave their GPS systems off. That is likely to distort the overall figures as they may use routes that have less congestion on them than the route the GPS would select.

5. It can disproportionately impact on smaller cities. As an example if you’re in a larger city and have a 45 minute commute however congestion delays you by 30 minutes that equates to a 67% congestion rate however if you are in a smaller city and you’re commute is only 15 minutes and you get delayed by 15 minutes that’s a 100% delay despite the hold up being half of what the bigger city experienced.

It’s starting to get a bit old now however there’s a good piece on the issues with the methodology in this piece from Reuters, some of which is covered above.

Lastly in the email I received about it they also mentioned this

Of the 138 countries surveyed for the Traffic Index, a global average congestion rate of 26% was recorded, placing New Zealand above the average with a rate of 28%. To put things in perspective, Wellington and Auckland even beat out New York City (39th) in the global rankings, a thriving metropolis of 8.4 million.

So we have worse congestion than New York, a city where the majority get around by methods other than a car and who in recent years has been reclaiming road space for pedestrians, cyclists and buses. Perhaps we should do more of that.

Lastly if we really want to move people around then then the Congestion Free Network would allow people to do that completely free of congestion giving some real choice.

CFN 2030A

TomTom’s Congestion Index Report

TomTom have released their annual congestion rankings and reported that Auckland is the 17th most congested city in the world.

The City of Sails is fast becoming the City of Snails, and is rising on a list of the world’s most congested cities compiled by navigation firm TomTom.

The report, which compares congestion levels in 169 cities across six continents, found New Zealand cities were experiencing some of the biggest increases in congestion.

On the list of the most congested cities, Auckland is ranked 15th, Christchurch 17th and Wellington 37th.

New Zealanders now spend a staggering 101 hours annually in peak-hour traffic, with Auckland having the biggest increase in congestion across Australia and New Zealand.

The congestion level for Auckland is measured at 34 per cent in the last June quarter, up from 30 per cent the year before. In Christchurch and Wellington it is 32 per cent and 28 per cent respectively.

At its worst, Aucklanders are stuck in traffic for an average of 47 minutes for each hour driven.

That all sounds pretty bad but is it really? First it pays to look at how they calculate the congestion index. The reports – which can be found here  – state that it is calculated as:

With the publication of the TomTom Traffic Index we are aiming to provide the general public, industry and policy makers with unique and unbiased information about congestion levels in urban areas.

The methodology that is used in this report compares the travel times during non-congested periods (free flow) with travel times in peak hours. The difference is expressed as a percentage increase in travel time. We take into account local roads, arterials and highways. All data is based on actual GPS based measurements for each city the sample size is expressed in total number of measured miles for the period.

Straight away there is a major issue with this methodology and that is the comparison is based in just how fast you can travel if no one else was on the road compared to what happens at the during the peak period. This is a serious issue for a few reasons.

1. Cities that have a lot of all-day congestion won’t appear as bad on the report because there is less of a difference between free flow and congested periods.

2. Many of our roads have been built to try and handle peak congestion periods and are relatively empty off peak allowing for much faster speeds. The motorways are a great example as they are often bursting at the seams during the peak but can be comparatively empty off peak allowing for much much faster journeys. The Northwestern motorway is perhaps the prime example of this and is now going through another round of widening.

3. The biggest issue though is that by comparing travel times by in this manner, it ignores what the most efficient speed for moving vehicles is. By that I mean over the same stretch of road more people overall can be moved if they are travelling slow than if they are travelling 100km/h. This is something that was picked up strongly in the research conducted for the NZTA by Ian Wallis and Associates which looked at the cost of congestion. They noted the differences between the definitions of congestion as:

Various definitions of congestion were reviewed and it was found that the concept of congestion is surprisingly ill-defined. A definition commonly used by economists treats all interactions between vehicles as congestion, while a common engineering definition is based on levels of service and recognises congestion only when the road is operating near or in excess of capacity. A definition of congestion based on the road capacity (ie the maximum sustainable flow) was adopted. The costs of congestion on this basis are derived from the difference between the observed travel times and estimated travel times when the road is operating at capacity.

The graph below shows the engineering definition mentioned above.

speed-flow

4. The TomTom report misses one key aspect and that is the ability of people to travel congestion free. Investments in the rail network, Northern busway and even just some of the bus lane network in the old Auckland City Council area have led to dramatic rises in the number of people using Public Transport. In the case of the busway, it has seen the number of people crossing the harbour bridge increase from 18% in 2004 to 41% in 2011. These people are travelling almost completely free of congestion (with the notable exception of in the city centre) yet the amount of time they spend on their commute isn’t captured by this data at all because they are almost certainly not carrying a TomTom with them.

bus-trips

Instead of being a congestion index report, what the report really should be called is a private vehicle travel time variability report.

I do note some interesting responses in the articles about the report. In the herald we get

The New Zealand Transport Agency said it was working to improve traffic flow in cities through investment in public transport services and infrastructure, roading and facilities.

“Our investment in public transport is at unprecedented levels, having risen by over 20 per cent nationwide in just three years,” said agency spokesman Anthony Frith.

“We’re also investing in walking and cycling facilities that will get people out of their cars and onto their bikes or travelling by foot.”

In Auckland, the agency was investing $3.4 billion in the region’s transport system, including $1.6 billion for state highways, $968 million for roads and $890 million for public transport.

Well most of the increase in costs for PT are to pay for the NZTA’s share of the loan for the new electric trains. I’m not saying that isn’t welcome but not necessarily the massive investment suggested. Further a small fraction of that is going towards PT infrastructure.

And from Stuff:

Automobile Association principal infrastructure adviser Barney Irvine said a focus needed to be put on getting more out of the existing network.

“Public transport is an important part of the puzzle but it is only one part.

“The big thing is to try and get more out of the existing network.”

Mr Frith said several initiatives were in place to try to ease congestion in all of the cities.

Auckland had a $3.4b programme of investment in the region’s transport system from 2012 to 2015. This included improvements to state highways, local roads and public transport.

I agree that we need to get more out of the existing network and it’s good to see the AA acknowledging that.

Lastly if we really want to move people around then then the Congestion Free Network would allow people to do that completely free of congestion giving some real choice.

CFN 2030A