Hi, I'm Soma. Catch me at @dangerscarf.

Live in NYC? I'm teaching a data visualization course at Brooklyn Brainery in April!

The Important Numbers on the PPW Bike Lane

The Prospect Park West bike lane has generated a lot of controversy, and I don't understand why. I looked at an ugly PDF full of numbers from the DoT about it, and it's made the street safer for bikes, pedestrians and cars.

I made this page this morning so you don't have to look at that ugly PDF. I'm not some crazy bicyclist, I'm just a guy who'd rather not get hit by anything with wheels.*

* Yes, that includes bikes.

Shortcuts: Speeding, Sidewalk Safety, Bike Lane Popularity, Salmoning, Car Throughput, Congestion, Safety, Conclusion, Who am I?, Math + Data


The DoT measured the speed of 100 cars morning, afternoon and night.

Before the bike lane...

Almost 3 out of 4 cars were speeding.

47 of those cars were going at least 10 miles over the speed limit.

After the bike lane...

Speeding was reduced by 75% to 1 out of 5 cars.

Only 2 cars went 10 miles faster than the speed limit.

CONCLUSION: Cars used to speed like crazy, now they are not speeding like crazy. Everyone is safer.

Sidewalk Safety

Riding a bike on a sidewalk is four times more dangerous than cycling in the road, and any accident has a greater chance of involving pedestrians.

Before the bike lane...

Almost half of all bikes rode on the sidewalk.

After the bike lane...

Only 3% of bikes rode on the sidewalk.

CONCLUSION: Bicyclists used to be idiots, but now they've stopped riding on the sidewalk. Sidewalks are much safer for people and their tiny dogs. Bicyclists are safer by not being on the sidewalk, too.

Bike Lane Popularity

It doesn't have to do with safety, but seeing how used the bike lane is might tell us something.

Before the bike lane...

Around 349 cyclists used PPW on a given day.

After the bike lane...

Around 1010 cyclists used PPW on a given day.

94% used the bike lane.

CONCLUSION: The number of bicyclists on Prospect Park West basically tripled. I doubt anyone started biking because of the bike lane, so I'm guessing they were on other, more dangerous streets beforehand. I think "popular and safe" is a rare combination.


Salmoning is riding a bike against the flow of traffic. It's dangerous, obviously.

Before the bike lane...

Almost 5% of all bikes rode against traffic.

After the bike lane...

Only 2% of bikes rode against traffic*.

* Yes, the 'after' cyclists salmoning are eschewing the bike lane to ride against traffic on the road.

So as not to be deceiving: 16 were counted before the lane and 19 were counted after, so the actual number of salmoning cyclists between those 2 days actually increased.

CONCLUSION A: We tripled the number of cyclists using PPW, but halved the percentage of them riding against the current.

CONCLUSION B: Yes, raw numbers are up, but I'd bet you anything that some of those 600 extra cyclists were previously salmoning up other streets.

Car Throughput

The DoT counted cars during peak hours.

Before the bike lane...

1,055 cars went by Carroll St between 8-9 AM, and 1,035 cars went by 11th St between 4-5 PM.

After the bike lane...

1,109 cars went by Carroll St between 8-9 AM, and 1,008 cars went by 11th St between 4-5 PM.

CONCLUSION: I'm sorry there isn't a chart, but that's because pretty much nothing changed. Even people who don't walk or bike aren't really being affected by the bike lane.


The DoT timed driving from Union St to 15th St during peak hours.

Before the bike lane...

On average, during peak hours, it took 2:49 to get from Union to 15th.

After the bike lane...

On average, during peak hours, it took 2:50 to get from Union to 15th.

CONCLUSION: Yes, it takes 1 second longer.


Wow, I somehow missed the 'Safety' section of the PDF the first few times through.

Before the bike lane...

On average, there were 29 crashes every 6 months, and 5 of them involved injuries.

After the bike lane...

There were 25 crashes in a comparable 6-month period, with only 2 causing injuries.

The bullet points contained the most the interesting part - there have been no pedestrian injuries since the bike lane was installed.

CONCLUSION: There are about 15% fewer crashes, as well as a very reduced chance of them resulting in injury, despite the fact that there are three times as many cyclists using the same space. I'm kinda impressed.

The Ultimate Conclusion

By adding the bike lane, unsafe behavior by both cars and bikes has plummeted. That's safer for everyone.

Beyond being safe, it hasn't caused any problems for motorists. Same number of cars, same time to get down the street; everything's working just like it was before, except everything's safer.

I hear these days the anti-bike-lane crowd is trying to make the bike lane only go one way. It's probably just going to make cyclists go back onto the sidewalk and cause more trouble there, or go down less safe streets that don't have bike lanes (7th Ave is pretty bad news like that). If you don't like bikes, at least now you've got them contained.

Et Cetera

Howdy, I'm Soma!

I'm a developer living in Fort Greene who does a lot of work with data. You can check out other things I'm up to at xoxosoma.com or on my tumblr. Questions, comments, and death threats/love letters can go to @dangerscarf or jonathan.soma@gmail.com.

If you think learning stuff is awesome but you hate spending money, you should check out Brooklyn Brainery, a super-cheap school I help run down in Carroll Gardens.

Math + Data

All of my data is from the ugly PDF from the Department of Transportation. If you'd like the excel sheets I made to do the mathy bits, just drop me an email.

I think the only math I did on my end was for bike counts (I used the 6/9/09 and 10/12/10 sets), averaging the peak AM and PM times under 'Congestion' and counting how many cars were going 40+ MPH. If you'd like to nitpick about sample size or anything, I hear you on that, but these trends seem pretty clear.