How many people in Detroit bike? How has this changed over time?

They’re very popular questions. The truth is we don’t know. Nobody does.

And that same answer is true for most American cities – accurate bicycling data does not exist.

That hasn’t stopped some groups from pretending that it does.

If you read the recent Huffington Post article on Detroit, you may have seen this.

A 2012 report by the Alliance for Biking & Walking found the number of bicycle commuters in Detroit rose 258 percent over the last two decades.

Sounds good, right? The Alliance report says Detroit had 340 daily bicycle commuters in 1990 and 1,217 in 2009.

What the Alliance report fails to tell you are the margins of error, which really give you an idea how inaccurate these numbers are.

That 2009 number is 1,217 plus or minus 803. Yep, the Census says the actual 2009 number could be as low as 414, likely within the 1990 number’s margin of error.

Another thing to consider: The 2009 numbers are based on a Detroit population of over 900,000, which is off by couple hundred thousand people.

And while everyone acknowledges Detroit’s notable increase in cycling activity last year, the 2010 Census numbers show bicycle commuting dropped nearly in half to 651 plus or minus 424.

If this hasn’t convinced you these numbers are quite worthless, there’s more.

The Census numbers only includes those who are working and 16 years or older. The Census doesn’t count most people who combine modes (e.g. use the bus bike racks) or who bike only a couple times a week.

The Alliance for Biking and Walking were made aware of these Census discrepancies for Detroit, but for the most part they did not address them. That’s why Detroit chose not to participate in the most recent report.

Other cities

Other cities are making big strides in understanding bicycling trends and counts. They’re doing travel surveys and bicycle counts — both automatically and manually — at key bridges and intersections.

And in cities like New York, they’ve found their counts don’t match the Census numbers either.

Detroit’s done some bicycle counts around Woodward, in Southwest Detroit, and on the RiverWalk, but not enough to draw any major conclusions. It would great if some future bike lane projects (looking at you, E. Jefferson!) could get some automated counters.

Until then, there just aren’t any good answers.

The 2010 Census numbers are in and Detroit’s reported population dropped as expected.

The new Census number is 713,777, however that may rise. After all, SEMCOG’s December 2010 population estimate — a very accurate one the data experts say — was 762,789.

Mayor Bing posted on Facebook, “I am confident our count will be revised. We must confront the reality that Detroit is losing population and commit to operating differently.”

How does this affect bicycling in Detroit?

If there is a positive, this population count reconfirms what we’ve been saying about the city’s urban biking. Detroit’s roads are some of the most bike friendly in America because more motorists are leaving them. The Detroit Census count has not been this low since 1910. And though we have greater car ownership in 2010, we also have many more road miles, not to mention expressways.

That said, there are many downsides to a dropping population.

For one, Detroit stands to lose road funding, which means less opportunity for building Complete Streets.

State road funding is divided up in an overly complex formula based on decades of legislative tweaks. Still, each city and village receives a portion of road funding based in part on their population relative to the others. When a city’s population drops more than the other citys and villages, they get less road funding. We’re not sure how much Detroit will lose, but we know it won’t be welcomed.

And, Federal Surface Transportation Program Urban (STP-U) funding is distributed by SEMCOG based on population. Detroit stands to lose road (and ADA ramp) money here as well.

Fortunately, Census population counts do not affect Transportation Enhancements funding which helps pay a lion’s share of the Detroit bike lanes and greenway projects.

Still, the next Federal Transportation Bill may scale back all transportation funding to match gas tax revenues starting in 2012. If that happens everyone across the board will see cuts.

These are certainly challenging times.