Here's a chart showing the frequency of searches for "car sharing" from different countries.
Is no one looking for carsharing in the US and Canada? And what's going on in Genoa, Italy, anyway?
Fortunately, when you search by company name you see where people are looking for Flexcar:
And where they're looking for Zipcar:
From these two graphs it appears slightly more people in San Francisco are looking for Flexcar than Zipcar (although there's no scale on the graphs). Sorry, Google Trends doesn't seem to be able to list trends for City Carshare.
The Google Trends page also shows weekly searching volumes and attempts to relate it with Google News stories. You can do your own search of search trends at the LINK below
