First, the comments: if you're looking for operational data - hours per day of utilization, revenues, etc. - I'll tell you right now, there's ALMOST NOTHING on the web. The reason is not hard to figure out: most of the companies are for-profit and don't want their competitors doing exactly what you're trying to do - reverse engineer their business model. Nothing surprising about that, is there? You can try to do a little reverse engineering from Zipcar's old SEC filings (pre/post IPO), City Carshare's tax forms (they're a nonprofit) on GuideStar, and the financial statements in Mobility Switzerland's annual report (they're a cooperative).
What is on the web has a lot to do with the growth of the industry and the demographics of members and trip patterns, as it relates to impacts on urban transportation. Almost all of the information out there is about traditional round trip, station-based carsharing, since the first studies of one-way/on-demand carsharing and P2P carsharing are only now underway with results expected to start trickling out in the fall of 2014.
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The starting point for any research on carsharing is the 2005 study by Adam Millard-Ball Carsharing Where and How It Succeeds. This is the bible on round-trip station-based carsharing. Fortunately, you can download the entire book for free from the Transportation Research Board here. Really, start with this report whether you're a car rental company, a city government agency or a business major writing a report or a business plan.
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Some other sources to check out:
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CSA — The Car Sharing Association is a North American-based trade and advocacy group with a growing world-wide membership, which primarily serves as a forum for operators. Some of the most useful current information is from the presentations from their 2013 conference here.
My Twitter feed — You'll quickly see that I Tweet a lot more than I write blog posts. I cover current developments in carsharing and "new mobility", in general. My most recent Tweets are to the right.
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Frost and Sullivan — Martyn Briggs and his band of researchers at Frost and Sullivan have produced a number of very interesting reports about carsharing and future of mobility and the automotive sector in both North America and Europe over the past few years. Of course, they'd really like to sell you the full reports. Search their site for the latest press releases here.
CommunAuto — Special mention should be made of the extensive bibliography of both French and English research reports on carsharing, starting pre 1981 and extending to 2005. This is a gold mine for history buffs.
Slideshare — And while we're on the topic of slide decks, there are a number of Powerpoints on Slideshare worth looking at. I'd start with the one's that have the most views here.
For international research you mostly have to go to consultants like me or hope you find something useful at the websties of trade associations in various countries.
World Carshare Forum — Eric Britton has been interested in carsharing even long than I have and has been an inspiration to pioneers in the industry through the World CarShare Forum. But as carsharing has become well-established he's broadened his interests into more general sustainable mobility topics. He's tireless in just about every medium imaginable, Facebook, Linked In, etc. Well, worth a read.
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Australia — has several major carshares serving multiple cities. The Australian government has published several reports about carsharing over the years.
Japan — Not surprisingly, given the density and cost of owning a car carsharing has taken off in Japan with a major parking operator and car rental firm offering carsharing. In addition, there are many smaller groups offering EVcarsharing services, as well as experimental programs from Toyota (Ha:Mo) and Nissan (Choimobi). Email me if you are interested in more information.
The rest of Asia — Without Google Search and GoogleTranslate, the scattered news articles about carsharing developments would be the inscrutable Orient!
And a final comment, do not overlook Wikipedia. Even I am constantly discovering detailed stuff on Wikipedia I'd never seen before.
Happy hunting. But don't say I didn't warn you! That's what we consultants are in business for - to help you sort out the wheat from the chaff - much faster and more economically.