Liu’s and Pucher’s Bike-Share Math Is Wrong, and Not By a Little

Hey, remedial math teachers: the City Comptroller’s office is hiring. At least, let’s hope so. Judging from Comptroller John Liu’s innumerate broadside against the City’s Bike Share program, they badly need help in basic arithmetic, not to mention fact-checking.

Let’s begin with Liu’s own words, insinuating that bike-share might cause one or more children to die:

[T]he rush to place ten thousand bicycles on our streets … risks significantly exacerbating the number of injuries and fatalities of both bikers and pedestrians, especially those most vulnerable like young children and seniors.

This is positively bizarre. Since you must be 16 or over to be eligible to ride a Bike Share bike, Liu must be positing collisions in which a Citi Bike rider strikes and kills a child. Yet that seems extraordinarily unlikely. No New York City child has died from being struck by a bicycle in memory, or at least since 1980, when I began tracking traffic crashes here. Moreover, by design the Citi Bikes will be ridden slower than bikes now on the road, making them even less likely to be involved in serious cyclist-on-pedestrian collisions. What, then, could Liu possibly be referring to?

But the numerical piece de resistance in Liu’s press release is this quote from Rutgers Prof. John Pucher:

Safety concerns about Citi Bike stem from frequently blocked bike lanes, poor street conditions, inexperienced bicyclists, lax enforcement of traffic regulations, and the inevitability that some users will ride on sidewalks. On the basis of these traffic dangers, I would expect at least a doubling and possibly even a tripling in injuries and fatalities among cyclists and pedestrians during the first year of the Bike Share program in New York. (emphasis added)

A doubling in injuries due to bike-share? At present, on an average day approximately 650,000 bicycle trips are taken in New York City — around three each by the roughly 180,000 New Yorkers who pedal on any given day, more by bike couriers and food-delivery riders. We can expect bike-share in its first year to increase this figure by 42,000 trips. That’s based on 7,000 Citi Bikes this year, and six trips per bike per day. (London and Washington, D.C. report 4-5 rides per shared bike per day, with 6-7 in Mexico City.) Since the increase in bicycle trips from bike-share is 1 part in 15, for the program to double the daily rate of collisions, whether with cars or pedestrians, or icebergs for that matter, each Citi Bike rider would have to be 15 times more likely than a cyclist on a regular bike to crash into something or someone.

That’s a tall order. In fact, the scenario it depicts is patently absurd, even allowing for bike-share’s concentration in the heavily pedestrianized and congested Manhattan Central Business District. Why, then, is Prof. Pucher, a leading U.S. scholar on global progress in urban cycling, promoting it?

I think there are two reasons. One is that like many people who aren’t grounded in day-to-day cycling here, Prof. Pucher doesn’t grasp the true extent of NYC cycling at present. Indeed, in much of his academic work Prof. Pucher has slavishly adhered to U.S. Census “commute mode” data that ignore the multi-dimensional nature of cycling here — for errands, meetings, socializing, appointments, shopping, exercise, and just plain fun — and thus end up lowballing bicycling’s “modal share” by a factor of around four. This leads him to ascribe to bike-share an outsized increase in cycling and, hence, an outsized increase in cycle crashing.

The other factor is more speculative, and here I draw on my association with Prof. Pucher since 1998, when I co-authored one of his early journal articles, contrasting the then-glacial pace of cycling improvements in U.S. cities with cycling’s high civic status in Europe. I would guess that Prof. Pucher is so appalled at the NYPD’s failure to safeguard cyclists’ legal right of way and offended by many cyclists’ defense mechanism of bending or even ignoring traffic rules altogether that he is unable to view a big new boost in cycling here in full context. And of course when he speaks to the press and electeds, the first part of his message, about protecting cyclists, is roundly ignored, while the second, warning of disaster, gets played to the hilt.

Hopefully, Prof. Pucher’s fantastically dire predictions won’t derail the bike-share rollout. And perhaps in time he’ll learn how to hone his message to the world outside academe. It’s Comptroller Liu’s office that should know better than to broadcast such patent nonsense. After all, bike-share isn’t a toxic debt instrument or a contagious disease. It’s a bold but proven program to give city dwellers another transportation option, one that is affordable, city-positive and healthful — not to mention good for the city’s bottom line.


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