Ever since Dorothy Rabinowitz’s anti-bike rant video in the WSJ lit up the internet on June 1, various bloggers have been trying to rebut her many dubious claims. Some of them, such as the claim that cyclists are a greater danger to pedestrians than taxi cabs, are flat out ridiculous on their face. The claim that cyclists have been allocated more than their fair share of space of NYC roads is no less false, but a bit less obviously so. Some, like Slate, appeal to intuition and call it a day. I found Better Institution’s Shane Phillips’ attempt at an actual calculation far more satisfying, but I think he made two really big (and unnecessary) simplifications which happen to work in opposite directions. First, he counted multipurpose vehicle travel lanes as car space, but this space is also used by taxis, buses, and, of course, bicycles. Second, it doesn’t take into account the fact that parking lanes (and cars themselves) are *much* wider than typical bike lanes. Most bike lanes were squeezed into already overly wide travel and/or parking lanes.

My modification to his calculation will look at the ratio between private car parking and bike lanes *in square feet*. This, I believe, is the number that should be compared to the ratio of private car occupants to cyclists. Phillips proxies for this with the ratio of commuter modal shares of cars and bicycles in NYC. I’m not really sure how to measure the impact of that proxy, as there’s a fair number of non-commuter cyclists and drivers out there, even during rush hour when road space is most at a premium, so I leave it as is. The mode share of bikes is 0.83%, and 26.7% for cars. Therefore the ratio of car to bike infrastructure to reach in order to be *fair* to cars is 32.2. Any less would be unfair to cars. Even so, I would argue cities should aim for an even lower ratio because driving causes greater negative externalities, such as traffic injuries/deaths, pollution, and damage to roadways, but let’s just say we are definitely *not* being fair to the bike if we are exceeding that ratio.

The DOT’s website states that the city has authority over 6300 miles of roadway. The state and federal governments are also responsible for a few hundred miles more, but I don’t believe any of them have parking. NYC is also directly responsible for a few highways, such as the Belt Parkway. Some local streets also don’t have room for parking, or have room for only one lane of parking. Overall, I would estimate about 85% of the 6300 miles have parking, and perhaps 10% of that has parking on only one side. For a given mile of roadway with parking potential, I would estimate, based on nothing more than my personal observations, that only about 70% is available for parking, with the rest given over to fire hydrants, curb cuts, bus stops, daylighting at intersections, etc., though many of the curb cuts are for garages, so let’s raise the proportion to 80% devoted to car-related uses. On the flip side of that, a number of streets have angle parking, taking up a greater proportion of the width of the roadway. Bottom line, I estimate that there are 8064 street miles, or 42,577,920 feet, devoted *exclusively* to private cars. Given the typical mix of angle and parallel parking spots, the average parking spot is probably 13 feet wide, totaling 553,512,960 square feet of our public streets devoted to cars.

On the bike lane side, the city claims 600 miles of bike lanes, but many of those are just sharrows which do not reallocate space so much as make drivers aware of the status quo on any street, which is that bicycles have a right to ride in a travel lane. The city also maintains 100 miles of greenways, but the city and state also maintain quite a few more miles of car-only highways, bridges, and tunnels, and neither greenways nor highways cannot be reallocated in a pinch. Therefore I will follow Phillips and say there are 300 miles of “on-street” bike lanes. The vast majority, say 80%, are 3-foot wide, with no more than 20% 10-foot wide protected lanes; an average width of 4.4 feet. Multiplying this width by the length of bike lanes (in feet), we find 6,969,600 square feet.

Finally, we find the area ratio of car to bike infrastructure to be 79.4. And there we have it, NYC streets are not nearly blanketed enough by bike lanes considering the number of people using them. And, like Phillips, I, too, left out many factors that would change the calculation to favor bikes even more, such as the fact that commuter modal share of cars vs. bikes has gone down since the survey was taken in 2010, center lanes on many busy streets are virtually inaccessible to cars, and the greater negative externalities of cars.