Empty and full stations abound in this cash-strapped system.

Thursday was the first day of spring. According to Ed Rademaekers, it was also the worst day of the year for NotSpots in New York City.

Rademaekers recently coined the term NotSpot to describe a Citi Bike station that's either completely empty or completely full. As of 10:30 a.m. on March 20, 63 of New York's 330 stations were NotSpots - 59 empty and four full. That's 19 percent of the stations in the system, meaning Rademaeker's NotSpot Index (tracked on bikeshareNYC) was in the red zone. The index goes from red down through yellow and green to blue, when less than 5 percent of the system is in NotSpot territory. Since Rademaekers launched his site in January, blue hasn't appeared much.

Rademaeker's NotSpot Index

This imbalance is symptomatic of the larger challenges facing Citi Bike, the nation's largest bike-share system, which has proven hugely popular but is struggling financially. As detailed in an article in today's Wall Street Journal, software glitches and damage from Superstorm Sandy took an early financial toll on New York's bike-share. A tough winter resulted in a sharp drop in daily passes which provide much-needed revenue for the system. And though annual memberships have soared to 100,000, many think that they're underpriced at $95.

The plan was always for the system to be subsidized by sponsorships rather than city funds. But apart from the initial investments by Citibank and MasterCard, there have been no major takers. And new NYC DOT Commissioner Polly Trottenberg acknowledged earlier this month that Citi Bike faces "a number of financial and operational challenges" and that "all options are on the table," including user rate hikes, to bring in more cash.

All those financial constraints led to layoffs over the winter, the Journal reports, which may account for situations like the one Rademaekers noted going into the first day of spring, when the 31-dock station at Allen Street and East Houston on the Lower East Side sat empty for 11 hours.

Rademaekers is a retired journalist and big fan of bike-share. He splits his time between California and New York, and when he's in residence at his apartment in Lower Manhattan, he uses the system whenever he can. "I use it in place of the subway to do the errands that need to be done," says Rademaker. It didn’t take long for his annual membership to pay off. "I kept close track of times that I would have been on the subway," he says. "The 99 dollars paid for itself in three months."

Like anyone who depends on bike-share for transportation, Rademaeker has experienced the sinking feeling you get when the station of your choice is empty, or worse, full. He started to get curious about the patterns of use, and what it would take to keep the system properly balanced.

Then Rademaekers stumbled upon the maps created by Oliver O’Brien at the Center for Advanced Spatial Analysis in the United Kingdom. These wonderful visualizations use open data to track bike-share systems around the world.

Now, every day, Rademaekers plugs the data from these maps into spreadsheets, creating a running graph of the availability of bikes. He has grown accustomed to the rhythm of the bikes as they move around, noting that the rush comes later than he would have expected, between 10:30 a.m. and noon.

Balancing the number of bikes in the system is one of the primary headaches of any bike share, and New York has been no exception. "More bikes end up in one part of the city, and they don't walk themselves back," he says. That’s a crucial problem. Here's how Rademaekers puts it on his blog:

We believe that the system has a decent chance to become as necessary a part of the public transit mix as a taxi or an A train. That can only happen if bicycles are consistently available in all served neighborhoods. And all served neighborhoods must be served equally. Right now, neither condition is being met.

Speaking to the Journal, Caroline Samponaro, with the advocacy group Transportation Alternatives, said: "The bottom line is that New Yorkers deserve better ... The arc should be improving."

Even before the winter and its discontents, balancing has been hard in New York. People were using the system in huge numbers almost immediately, and certain key points in the network were quickly overwhelmed. At Penn Station, as WNYC pointed out in their story about the problem last summer, truckloads of bikes were being brought back to the busy commuter hub twice during the course of a morning, but it still wasn't enough. (The station has its own nifty map showing usage patterns at individual stations.)

"Rebalancing is an ongoing challenge for any successful bike share system," writes Dani Simons, director of marketing and external affairs for NYC Bike Share. As she explains:

"With over six trips per bike per day on Citi Bikes during the warmer months, keeping the bikes and docking points available to our customer where and when they want them is always going to be tough. We are using data we collected last year to try to build better routing plans for our re-balances, staging bikes near some of our busiest locations (e.g.  near Penn Station and the Lower East Side) and even experimenting with moving small numbers of bikes more quickly using bike trailers this spring."

In a perfect world, every station would be half full and half empty, but Rademaekers recognizes just how complex the problem is. He’s hoping that his NotSpot index will provide a valuable way of visualizing the imbalances.

"I don’t want to put myself out there as the decision-maker about what is an acceptable service level," he says. "But if the blog started that conversation, that would be great."

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