Neighbors For Better Bike Lanes But Worse Math
Recapping some of the year’s big stories, something strange caught my eye in the recent NY1 piece naming Janette Sadik-Khan the NYer of the Year.
Here’s Norman Steisel and NBBL in their December 22, 2010 letter to the editor of the New York Times.
At Prospect Park West in Brooklyn, for instance, where a two-way bike lane was put in last summer, our eyewitness reports show collisions of one sort or another to be on pace to be triple the former annual rates.
Here’s Steisel in a January 1, 2011 story on NY1:
“Just five months since the bike lanes were opened, we’ve received eyewitness accounts of 10 vehicular accidents on Prospect Park West, which compares to an annual average rate of 8.8 for the preceding four years,” said bike lane opponent Norman Steisel.
There’s only one thing to point out here: 10 is not “triple” 8.8.
Being generous, the PPW bike lane “opened” in June 2010. So I’ll even give NBBL an extra month. There are two possible explanations for the discrepancy between Steisel’s two statements.
- While writing the first letter, NBBL and Steisel expected the remaining nine days of 2010 to be filled with an astonishing sixteen additional accidents of an unspecified type.
- NBBL and Steisel are lying.
Which explanation do you think is most likely?
UPDATE, 2:25 PM: It was pointed out to me that NBBL is extrapolating their five month-sample to the entirety of 2010, which I understand. Under nine accidents for an entire year versus 10 in just five months would, of course, be disturbing…if such stats were verifiable. Two big questions come up, even with this clarification. First, if the annual accident rate of 8.8 comes from DOT or NYPD stats, why is NBBL now relying on eyewitness accounts? Surely they could get their “after” data from the same place they got their “before” figures, no? Second, if the 8.8 figure comes from previous “eyewitness accounts,” why were they out collecting data years before the bike lane was installed, since most of them think that PPW was just fine without the bike lane? (Tom Vanderbilt has made a similar point.)
NBBL, if any of you are reading, please provide me with your methodology and I will gladly post your findings here, unedited.
I offer my apology for my shoddy analysis and slight misunderstanding of the data and my thanks to those whose tweets offered clarification.