Friday, September 27, 2013
Since my last post, NYC Bike Share has rolled out a System Data webpage, on which you can view and download substantial data on the system's usage thus far. The data is stored and displayed via Datawrapper; I'm not thrilled with the presentation (particularly the absence of tooltips to display exact values), but I'm surely grateful not to have to manually transcribe another three months' data off of blog posts. Data is available through Tuesday 9/24, so we have just over 17 weeks (and just under four months) to play around with.
Of course, the first step is to validate all this new data. I was dismayed to identify several glaring inconsistencies within the provided numbers. The System Data page includes both daily and total counts for trips taken, miles traveled, and annual memberships sold, plus daily sales of 24-hour and 7-day memberships – but on numerous occasions, adding a day's trips taken to the cumulative total thus far yields a number different than the next day's cumulative total. (Similar problems abounded for miles traveled and annual memberships sold.) Most egregiously, the cumulative numbers for July 18 reflect an additional 12,666 trips and 317,494 miles (= a highly unlikely 25 miles per trip!) beyond the provided daily figures. So I've used the numbers I'd collected from the blog, along with simple arithmetic and common sense, to reconcile the conflicting values; all my data is available here for the curious.
Having massaged our data into some semblance of consistency and plausibility, let's take another look at the key charts from my first post. (If you haven't read it, click here for background on why these figures are important.) It turns out that my first post, dated June 25, occurred right at the beginning of a substantial slide in membership sales. Around 6/23, users were purchasing nearly 2700 daily passes; by 7/10 that number had dropped 45% to under 1500. But at the same time, 7-day and annual membership sales made a comeback; since then, weekly memberships have continued to putter along (this is, perhaps, a category with limited demand; the new Bay Area Bike Share instead offers a three-day pass) while annual sales remain surprisingly robust for a system now beyond its infancy, and daily membership sales have stabilized around the 1500 mark. All in all, sales remain sizeable; when more information on the system's operating costs becomes available, I'll be able to assess whether they're bringing in enough business to cover costs.
System use is extremely strong. The 7-day average "high" of 29,091 trips on 6/24 has turned out to be a "low" in comparison with the system's subsequent performance: Since July 14, the average daily ridership has not dropped below 30,000. At the same time, though, the continued growth in active members has kept the "trips per active member" ratio in check. I had hoped to see that figure continue its dramatic mid-June climb, but no such luck thus far; it's hovering around 0.45 as peak cycling season comes to a close. (Expect that number to drop come winter.) If the system does expand as promised and hoped, active members across the city would be able to use Citi Bike for more trips in more areas, likely leading to a rise in the trips-per-active-member ratio. The unsmoothed data remain noisy, but there is at least one important trend they reveal. It is easy to pick out weekends – when 24-hour membership sales explode – and Mondays, when satisfied 24-hour pass buyers seal the deal by purchasing an annual membership. But in late June, the daily trip count, which had up to that point been closely correlated with 24-hour pass sales, decouples from short-term memberships and begins to stay high throughout the week. My surmise (and hope) is that by the end of the program's first month, annual members began figuring out how to integrate Citi Bike more fully into their daily transportation routines. In any case, daily trips have continued to rise even as sales of short-term passes decline with the end of peak tourist season.
(I promised earlier that I'd investigate the impact of weather on daily ridership; I've now made a preliminary survey and found that impact to be quite limited. I collected daily mean temperature, mean humidity, and total precipitation data from Weather Underground, then exported my data to run some linear regression and correlation analysis on it in R. I found that a simple linear model with total active members as the independent variable and daily trips as the dependent variable accounted for (i.e. adjusted R-squared = ) 76% of the variance in daily trips. Although correlation analysis indicated a weak negative relationship between humidity and precipitation and daily trips, a multivariate model incorporating the three weather measurements accounted for only 5% more of the variance – not a substantial increase in the model's predictive power.)
(If any readers with a strong statistics background want to chime in with a more nuanced analysis of the data, I'm all ears. The comments section is below and here's the spreadsheet.)
It's quite clear from these charts and figures that Citi Bike has been performing excellently over its first four months when compared with its first four weeks. But that is probably not a very useful context. (In the United States' first four Presidential elections, the runner-up became the Vice President.) Instead, let's see how New York's system usage stacks up against a successful and established program across the Atlantic.
London, population 8.3 million, has had Barclays Cycle Hire1 since 2010. With 8,000 bikes and 570 stations in operation, that three-year-old system logged 904,155 rides this August, split 50-50 between short-term riders and annual members; its all-time peak thus far was 47,105 rides in one day, during the 2012 Olympics. Meanwhile, a three-month-old Citi Bike, comprising 6,000 bikes and 330 stations2 in a city of the same population as London, recorded 1,115,340 rides in August, representing a whopping 6.0 trips per bike per day, 64% higher than London's usage levels. NYC's peak thus far was 44,083 rides on Saturday, August 18 – 94% of London's peak, which is not bad given the absence of any Olympic Games.
Data isn't yet available on the percentage of Citi Bike rides taken by annual members vs. temporary members (a division roughly equivalent to "locals vs. tourists" or "work vs. play"), but we can approximately assess the proportions of utility trips vs. recreational trips by examining how many trips occur on weekdays vs. weekends. (This is imperfect, of course – many locals make utility trips on weekends, and most tourists' weekday trips are still recreational in nature – but bear with me.) In May and June, weekends saw substantially more use than weekdays, but in the months since, weekday usage has equalled and often exceeded weekend ridership. Combined with the decoupling of daily rides and 24-hour pass sales we saw above, this leads me to conclude that Citi Bike is less and less dominated by joyriding out-of-towners. Will Citi Bike, having attracted more than 84,000 annual members in its first four months, manage to equal the Boris Bikes' three-year sales figure (186,762)? Almost certainly. About 250 people per day are currently purchasing new annual memberships, a rate that, if sustained, would push total membership sales past the 100,000 mark in just over two months; and when those annual memberships begin to expire next summer, count on the vast majority of users to re-up. Indeed, I am predicting here and now that by June 1, 2015, Citi Bike will have sold more than 200,000 annual memberships.
So: given Citi Bike's burgeoning ridership, its favorable performance compared to London's longer-established system, and the strong support/warm acceptance shown it by New York's mayoral candidates, it looks like bike share is here to stay.
How has bike share been treating you so far? Are there any other bits of analysis you'd like to see in future updates?
1 I always find it so funny that "bike share" has exactly zero words in common with the British English equivalent, "cycle hire." I'm also amused that what we Americans call a "system" the British call a "scheme," which always sounds slightly sinister. ("Cycle to Work Scheme: brought to you by the All-Powerful Bike Lobby") ↩
2 Officially, the system has 6,000 bikes. However, a fabulous visualization by Jehiah Czebotar suggests the true number is currently closer to 4,100 – which would mean that New Yorkers put in almost nine trips per day on every Citi Bike this August. ↩
Tuesday, September 24, 2013
OK, back? Good. I mostly want to talk about the diagram, reproduced in teensy size to the right. Notes:
- 2 and 3 are the same thing.
- In Manhattan, the 1st/2nd and 8th/9th Avenue bike lanes have features 1-4 (and cyclists love 'em!). Those lanes are among the best cycling infrastructure in the United States, and their appeal to novice cyclists is a testament to the effectiveness of the "Dutch" approach.
- I'm ambivalent about 6, unless the cyclists get the light slightly before drivers (allowing them to safely establish a presence before right-turners cut them off). Berlin has bike-specific signals, too, and the timing is staggered in this fashion at major intersections, and it works; but it's important to remember that Germany and the Netherlands are fundamentally more law-abiding cultures than the US, and that American cycling is still seen as something of a Wild West, so it may be quite some time before cycle-specific signalization gains traction, but I guess you have to start somewhere, if you want the American endgame to look like the Netherlands.
- 7 is not a feature of Dutch cycling infrastructure but rather a byproduct (and partial enabler?) of the ubiquity of utility cycling in the country. It was perhaps unwise for the Globe to bring up this issue, one of the most contentious* in the bike advocacy world. Shall we dismiss Australian utility cycling as doomed to fail, given that country's universal helmet requirement?
- The real game-changer, as far as infrastructure goes, is 5, which could greatly diminish the incidence of right hooks. (One of the strongest arguments advanced by vehicular cyclists* is that separating bikes and cars using cycletracks actually decreases cyclists' safety at intersections, when they "suddenly appear" from directions drivers aren't expecting.) 5 is an elegant physical solution to that problem.
- A key moment in the Dutch adoption of utility cycling was a nationwide moratorium on Sunday driving caused by the 1973 oil shortages. I've long admired the collectivist spirit of northern European democratic socialist societies; the last time the American government mandated consumption reductions was the rationing during World War II. (Some municipalities, like the Bay Area, now have voluntary air-quality improvement programs, but voluntary just isn't enough for the vast, silent majority of the population.) In the US, the approach is to gently change the market and societal incentives to encourage a transition to cycling, an approach that appears to be working. But it's fairly slow, and I have a hunch that a lot of people out there would take to utility riding if given the nudge. ("A transportation liberal is a conservative who's taken one ride on a Citi Bike.")
- The Dutch system of school-based cycling instruction and a "bike diploma" at around age 12 is wonderful. I had the good fortune of being raised by a mobility specialist, so had a very strong grounding from a young age in matters of street safety. I think such pedestrian/bicyclist education is very important, but I also feel strongly that there should be no legal licensing requirement for bicyclists. (They just don't pose enough danger to merit such a requirement.) But formalizing the education and training process - and making it as integral to primary school as driver's education was at my high school - is such a good way to disseminate life-saving information throughout society.
* I don't want to get into the vehicular cycling debate, or the helmet debate, at least not here. But I surely will, down the road.
Saturday, July 6, 2013
I am a city person. I live in a city, I spend all my time thinking about and studying cities. But every so often, I like to punctuate that existence with a sharp contrast, so I'm off to raft the Rogue River, in southern Oregon, with family and friends. I'll be back on July 15 with some observations from San Francisco.
Tuesday, July 2, 2013
The horrendous bicycle congestion in Amsterdam (“The Dutch Prize Their Pedal Power, but a Sea of Bikes Swamps Their Capital,” Amsterdam Journal, June 21) portends my worst fears for New York City if Mayor Michael R. Bloomberg’s crusade to promote cycling at any cost is not scaled back by his successor.In addition to the ubiquitous tombstone-like parking stands for the new bike-sharing program, Citi Bike, more and more bikes are appearing on our sidewalks, clumsily chained in bunches to anything stationary, cluttering pedestrian areas and complicating emergency services, trash collection and sanitation.The density and vertical nature of our city mean that hundreds of cyclists could live, and park, on a single block, leaving neighborhoods with all the charm of a junkyard.Cycling should be neither deterred nor promoted, but certainly not singled out as a privileged mode of conveyance whose operators enjoy segregated lanes, free parking and exemption from the licensing, insurance and safety precautions (like helmets) required for other two-wheeled vehicles such as motorcycles.
|(The best Venn diagram ever.)|
Gary Taustine should have his eyes checked. He sees more and more parked bicycles, and "tombstone-like" Citi Bike docking stations, but apparently is oblivious to bikes in motion, and to the hundreds of thousands of New Yorkers who ride them for transportation, work, and pleasure throughout the city.
He also appears not to be able to see the signs permitting free on-street parking for private cars in our dense city. A bicycle locked neatly to a Department of Transportation-provided bike rack, taking up no more than four square feet of space, catches his eye, but the hundreds of square feet allocated to each car parking spot (some of the most valuable real estate in the world) are invisible to him.
Most of all, Mr. Taustine cannot see the need, and the desire, for change in how New Yorkers get around. The number of commuters cycling to work has quadrupled since 2000; thousand-year storms are battering our shores more and more frequently; more and more citizens now share the same dense streets, and need to do so in space-efficient vehicles.
Mr. Taustine sees bicycles - and the change they represent - as a menace. Perhaps he should take another look.
Tuesday, June 25, 2013
I'm working with data published daily on the Citi Bike blog, including some useful figures (daily trips, new membership sales) and some of questionable value (daily miles, average trip duration, most popular stations). That latter category is not totally useless: over the weekend, the system reached the fun milestone of 1 million miles traveled, which makes for good press; and I suppose you could calculate the average systemwide speed, [EDIT: I did this just for kicks, and it's a mess. See below.] but it's the former on which I'll focus in an effort to track Citi Bike adoption and penetration rates.
Let's begin with the raw data. Every day, the blog provides sum totals of annual memberships sold, miles traveled, and trips taken. Antonio D'souza has been graphing these numbers:
In fact, it was Antonio's graph that inspired me to dig a little deeper into the Citi Bike numbers. Graphing the total figures for each day is good if you just want to show that the system is getting use, but it's not particularly revealing. Since these are totals since inception, they will of course only ever increase. Instead, we want to examine daily differences - the first derivative of the total numbers - to see whether the rate of growth is increasing.
Some daily increments are given on the blog (such as daily trips taken), and it's easy to derive the rest by subtracting, for example, total annual members on June 22 from total annual members on June 23. Here, then, is a chart of new membership sales and trips taken per day:
As you can see, this is quite a noisy graph. The fact that there is so much daily variation makes it difficult to discern longer-term trends. For instance, was the system somehow four times better or more appealing on 6/9 than 6/7? Certainly not; 6/7 was very rainy, and 6/9 was a beautiful Sunday. We will examine the weather/trips relationship in a future post, but let's now deal with the weekend effect - the spike in ridership that occurs, unsurprisingly, on Saturdays and Sundays.
(It's interesting to note in passing that daily ridership initially tracks quite closely with daily 24-hour passes sold, but has begun to diverge in the past week. This new trend, along with the recent strong weekday ridership, could be an indication that annual members are making more extensive use of the system - in particular for utility trips during the work week. Enabling such utility trips is a key goal of the system.)
To neutralize the weekly periodic fluctuation in Citi Bike data, we will calculate a rolling average over 7 days around each data point. This way, each number will reflect the average value over each day of the week. Financial applications usually use a trailing average, in which each point takes the average of the preceding 7 days, while scientific analysis generally employs a centered average, taking the mean of the week centered on the date in question. Here's what each of those options looks like with our data:
This chart makes clear the advantage of the centered rolling average: as Wikipedia notes, it "ensures that variations in the mean are aligned with the variations in the data rather than being shifted in time." (The trailing average is three days behind the centered average, which results in consistent underestimation when the data are generally increasing, as is happily the case with Citi Bike usage.) The chart also demonstrates how the rolling average neutralizes the periodic peaks and troughs on weekends and weekdays.
(By the way, ridership has been substantially greater on weekends than weekdays. Here are the average number of trips per day of the week:
- Sunday: 23,615
- Saturday: 18,196
- Thursday: 17,030
- Friday: 14,359
- Wednesday: 14,214
- Tuesday: 12,729
- Monday: 11,480
Now that we have identified the data of interest (measures of change over time) and smoothed them to eliminate periodic noise, we can get down to assessing the success of Citi Bike's rollout in more detail. Let's look first at sales trends: how many new annual, weekly, and 24-hour memberships are being sold? Ideally, we'd want to see the 24-hour and weekly numbers steadily increasing, and the annual numbers holding steady or falling only slowly. (It's unreasonable to expect that annual sales won't drop off as the buzz from the launch subsides and the early adopters complete their early adoption.)
The data suggest that Citi Bike is performing quite well as measured by sales. Daily sales of 24-hour memberships have bounced around 2,100 for some time, but have recently skyrocketed; it remains to be seen whether that trend will hold up going forward. Weekly memberships initially failed to gain traction, dwindling to only 170 sales on 6/10, but have since gained traction, hovering around 400 daily sales since 6/19. Sales of annual memberships did see a fairly rapid, steady fall after launch, but stabilized around 6/10 and remained encouragingly flat through 6/20, since when they appear to have begun another slow decline. Even so, many hundreds of New Yorkers continue to join Citi Bike daily, nearly a month after the system's launch. This is heartening.
What about ridership? We know that people are buying memberships, but are they actually getting out and riding the big blue bikes? Let's compare the rolling average of daily trips to the number of active members (all annual members + new 24-hour members + 7-day passes purchased within the past week) on any given day. This figure - trips per active member - will serve as a rough proxy for Citi Bike's total mode share. (Rough, because 1 trip on Citi Bike does not necessarily imply 1 fewer trip on other modes, especially when the Citi Bike trip is recreational in nature. For instance, I recently took two trips on public transit in order to make several Citi Bike trips; but that's another story.)
This is perhaps the most heartening chart yet. As the total number of active members climbs steadily, the number of daily trips has dramatically risen (from about 12,500 on 6/10 to nearly 30,000 on 6/23), with a concomitant surge in trips per active member from a low of 0.32 to a recent high of 0.57. We may hope to see the trips-per-active-member figure continue to rise (surmounting 1.0 would be a great milestone), but the data so far suggest that Citi Bike is already becoming more and more important in the daily lives of its members.
What's next in Citi Bike data analytics? The interactive charts in this post will continue to update as more data becomes available over time, but of course my commentary will not automatically adapt to reflect new trends. I'll try to check in every so often and address recent developments as Citi Bike continues to expand its presence in NYC. You can always visit my Google Spreadsheet to see the latest numbers.
Of course, I'm not the only one exploring Citi Bike data. Greg is doing some great work analyzing the live station activity feed, and he's identified the most popular neighborhoods and come up with some good insights on best balancing practices. OpenPlans and betaNYC are holding a Citi Bike data night tomorrow. And there's a lot more data on the way, if NYC Bike Share makes good on its promise to follow Capital Bikeshare in releasing a web dashboard (though I hope they don't bury their data in a Silverlight application).
EDIT: For fun, I calculated the daily average systemwide speed (based on the otherwise useless miles per day and average trip duration data points). Here's the graph:
This is troubling, because the values are so implausible. During the first week, the claimed average speed (on those bulky bikes) is around what I attain when I'm riding my road bike through the city in a hurry (I do stop for red lights, though) - that is, it's unrealistically high. After that, though, it gets even worse, as the speed is almost always given as 7.46 +/- 0.02. I find it very difficult to believe that Citi Bike users just happen to achieve almost exactly the same average speed day after day (albeit a speed that sounds realistic given the bikes and their riders).
I'm not sure what to make of this suspicious data. It certainly shows the need for independent validation of blog data (using, say, the JSON feed). I'll keep an eye on this, though, and maybe inquire about it at tomorrow's bike share data evening.
Sunday, June 23, 2013
|(Bikes, or yikes?)|
I've thought a lot about the end game for cycling as a mode in cities. Obviously bikes are much better than cars in terms of their environmental impact - pollution, noise, energy use, taking up lots of space. But one key problem - the domination of public space for the storage of private vehicles - remains an issue with bikes.
One piece of good news is that the day of reckoning is still way far off, at least for NYC. According to the article, 32% of trips in Amsterdam are by bike, a truly staggering mode share. (The current goal of the NYC Department of Transportation, the most bike-friendly DoT in city history, is for the cycling commuter mode share to hit 3% by 2020.)
I think there are two ultimate solutions to the problem of transportation in very dense environments. The first is a reliance on mass, rapid transit (i.e. subways and regional/commuter rail) for at least the backbone of most trips. Mass transit, as the name might suggest, has throughput rates that no other mode can even begin to approach. And if it's below grade (underground) or even above grade (but that's ugly; we took down the elevated railroads for a reason) it doesn't place heavy demands on street space, leaving that resource open for…
…paratransit - bike share and taxi fleets. One of the worst problems with cars is that they spend 97% of their time parked, rather than being in use. When that parking occurs in a dense urban setting, it represents a massive misuse of valuable space. (Why does Manhattan still have free on-street parking when adjacent condos are selling for $3,000 per square foot, and San Francisco realtors are selling garage spaces for upwards of $80,000?) Taxis and bike share are good because the vehicles are always in use or available for use, meaning the space they occupy is better utilized.
So ideally, trips in a central city would start on foot or via shared bike/car, connect to a high-throughput mass transit network, and end with a "last-mile" leg again on foot or by paratransit. (Or the shared bike or car trip could go the full distance, though that's somewhat less system-optimal, particularly in the case of the car due to the congestion it creates.) Outside the city? I care not; space is at much less a premium.
Denmark, as I understand it, actually works in much this way; many suburban Copenhageners own cars and drive them, for fun, on weekends, outside the city. Then they get back to transit and biking, much space-friendlier transportation modes, for their weekday utility trips.
So what should Amsterdam be doing to solve their (I can't believe I'm writing this) bike congestion problem? Building more bike parking is not a long-term viable solution, unless there's a sense that the 32% mode share is near the theoretical maximum (and I don't think it is) so parking needs won't continue to increase in future. Instead, they need to address the inefficiencies present in their city as indicated by the guy quoted in the article as having three bikes all locked up on public streets at the same time.
This misuse of public space has two good solutions: encourage a transition to bike share and begin charging for on-street bike parking. The Netherlands has a national bike sharing program, but it's smaller than NYC's system even as currently implemented (theirs totals 6000 bikes at 230 stations; we so far have about 5000 bikes at 300 stations and we're looking at 10,000 bikes and 600 stations hopefully by the end of the summer). A heavy expansion in central Amsterdam - we're talking a station at every other intersection - combined with an education campaign touting the benefits of bike share over private bike use (and there are many, not least of which is the nonexistent risk of theft) could get many Amsterdammers' private bikes off the road.
The bigger solution, and doubtless the more controversial in a city actually dominated by an "all-powerful bike lobby," is to charge bike riders for parking their bikes on public streets. This could be done through a system of handlebar-mounted permits (monthly or yearly for local residents or frequent commuters) allowing owners to lock up anywhere in the permit's district, and the installation of combined bike racks/parking meters for short-term use (ideally with an SFpark-style smart pricing infrastructure, so that prices can adjust over time to reflect local supply and demand). I envision the parking pricing remaining fairly low: the goal is not to raise money for the city, or to disincentivize biking, but rather to urge riders to store their bikes off the street - which would in turn invigorate private bike parking operations.
The bottom line is that in Amsterdam, cycling has become the new normal - which, thankfully, is the current goal here in New York and in an increasing number of cities. Cycling is an excellent urban transportation mode. But when it reaches the point where it begins to create the same problems that private car use has been creating for the past century, some of the same solutions are in order.
Does this suck? A little bit. One of the joys of the bicycle is the air of freedom it carries - the ability to zip nimbly through narrow streets, lock up to just anything, and get on with your business before the car driver even makes it past the choked expressway. I recently, after a debate with a fellow cycling advocate, made the decision to start riding not just according to the spirit of the law (don't endanger others) but also to its letter (stop for the full duration of red lights, at stop signs, etc.). I feel good about being part of the new, courteous face of urban cycling, but a little magic has gone out of the world for me.
In the end, though, it's not about the joy of riding (there's always suburban and rural roads for that sort of thing) but about the proper place of cycling in cities: safe, respected, ubiquitous - and regulated.
Where do you see cycling headed in NYC and Amsterdam?
Monday, June 17, 2013
Combine the no-JS rule with the fact that it costs $13 annually (!) to enable domain mapping, and you have a recipe for my switching to Blogger, which allows both features, for free.
My first few posts are still online here. I may migrate them over to this page at some point in the future.