11/06/2013 18:16 EST | Updated 01/23/2014 10:53 EST

Is Vancouver the most gridlocked city in North America?

A new study by GPS makers TomTom is being disputed, after Vancouver was judged the most traffic-congested city in North America, ahead of Toronto and Los Angeles.

The study's congestion index uses data provided by TomTom’sGPS users, to measure how long a commute takes in non-peak hours — for example, Sunday morning at 5 a.m., with nobody on the road — and then compares that number to peak travel times (for example, 5 p.m. on a Monday).

Vancouver scores an overall index of 36%, meaning 36 percent more time is required to drive at 5 p.m. on Monday compared to 5 a.m. on Sunday. The equivalent numbers are 35% in LA and 27% in Toronto.

However, Joe Cortright, president and principal economist for Impresa, a consulting firm in Portland, Oregon, has studied the question of traffic congestion and sees real problems with the TomTom study.

“If you live in Vancouver and have an average 15-minute commute and it takes an extra five or six minutes longer — that’s your 36% increase. If you live in Los Angeles and have a 45-minute commute and it takes you 10 minutes longer, that’s only a 20 percent or so increase."

Cortright says that the index doesn’t look at the distance people actually travel, or even the total amount of time they travel.

“A lot of the cities that do well in these surveys – sprawling cities like Birmingham, Richmond and Oklahoma City – people drive twice as far as people do in the average city,” he notes.

He doesn’t feel that such indexes are useful in comparing one city to another, as they doesn’t accurately reflect the commuting realities in each city.

Few would argue, for example, that commuting in a densely populated urban centre like Vancouver is the same as driving across sprawling cities like L.A., with a road network eight times Vancouver's size.

But Cortright does see value in looking at trends over time in individual cities.

“If congestion were increasing or decreasing in Vancouver over time, you could compare last year’s number to the next year’s number,” says Cortright.