Thursday, July 12, 2012

TomTom Congestion Index Useless for Metro Vancouver

My jawed dropped when I saw the headlines yesterday that Vancouver has the second worst congestion in North America. TomTom, the GPS maker, released the North American Congestion Index which found that Metro Vancouver had an index of 30%. It didn’t seem to make sense to me so I looked into the number. The congestion number is based on the percentage difference between free-flow travel time and congested travel time. So if three cities have free-flow travel times of 35, 30, and 25 minutes and during peak periods travel time is 5 minutes longer in each city, the city with the shortest free-flow travel time will appear to have worse congestion using the TomTom Index. Another fatal flaw of this report is that it does not take transit, cycling, or walking into account which in Metro Vancouver plays a large role during peak commuting times.

Information from Statistics Canada points to the link between population and commute time. The not-so-surprising result is that the larger the population, the higher the commuting time.

Average Commute Time vs Population (Source: Statistics Canada)

When you plot the average commute time to the TomTom Index, there is a weaker correlation that becomes glaringly obvious with Metro Vancouver.

Average Commute Time vs. TomTom Congestion Index (Source: Statistics Canada)

The big difference between Metro Vancouver and every other major region in Canada is that we have fewer freeways which means that the average speed in Vancouver is slower. Many people confuse speed and mobility with travel time and accessibility. While Vancouver roads are the slowest of any major region in Canada, yet we have shorter commute times than Toronto or Montreal. Metro Vancouver is a more accessible region.

What I did find really interesting about the TomTom report is the other data it contained. There seems to be a link between the amount of freeways built and congested speed. It seems that the more freeways you build, the larger the difference between free-flow and congested speed. You could draw the conclusion that freeways actually make more congestion!

Congested Speed vs Free-Flow Speed (Source: TomTom)

The TomTom congestion index is useful for the region that builds more freeways as its population grows and doesn't rely on public transit, walking, or cycling, but in a region like Metro Vancouver (which bucked the freeway trend until recently) the index proves to be of little use.

PS: The average commute time in the freewayless City of Vancouver is 27 minutes, while outside of the City of Vancouver the average commute time is 31 minutes.

The raw data. Click image to view.


Anonymous said...

A real embarrassment. Congratulations to all the major news outlet for biting on a marketing bait. A great example of the poor fact checking done by most daily news journalists. They certainly did not read the "report" before pushing the story.

Anonymous said...

I disagree with the claim that one "could draw the conclusion that freeways actually make more congestion," that graph instead suggests to me that more freeways increases congested speed, which imo should REDUCE average commute time.

I think it's also of note that Vancouver has a significantly lower average free-flow speed, something that our elected officials should be looking to change, by improving driver skills, instead of demonizing speeding to increase ticket revenue.

Unknown said...

Speed means the death of the street. We must slow ourselves to save ourselves. Chance of death when one is hit by a car go to almost 80% as soon a car go overs 50KM/H.

Anonymous said...

"Many people confuse speed and mobility with travel time and accessibility."
What do you mean confuse? Those terms are all interrelated, not alternatives.

Nathan Pachal said...

Not really, the ability to get from point a to b fast is difference then getting from where you are to where you need to go. Driving 15km to get grocery fast (mobility) is difference then being able to walk to a grocery store because it is close. (Accessibility)