According to Jan Garrard, a senior lecturer at Deakin University in Melbourne, Australia, the best way to determine how favorable a given city is for cycling is to measure the number of women bike-riders. From Scientific American:
Women are considered an "indicator species" for bike-friendly cities for several reasons. First, studies across disciplines as disparate as criminology and child rearing have shown that women are more averse to risk than men. In the cycling arena, that risk aversion translates into increased demand for safe bike infrastructure as a prerequisite for riding. Women also do most of the child care and household shopping, which means these bike routes need to be organized around practical urban destinations to make a difference.
Clearly, there are many exceptions to these generalizations, and many women are neither risk-averse nor taking children in tow. But in American cities without safe, well-defined biking infrastructures, men tend to bike a lot more. In most of New York City, for example, the ratio of male to female cyclists is three to one (though it should be noted that along the car-free greenbelts of Central Park, women make up 44 percent of riders). In European cities, on the other hand, where the infrastructure exists, the split is more even-in the Netherlands, where a lot of cycling takes place, women actually make up 55 percent of the ridership.
The idea of women as indicators is fascinating, but the main takeaway seems to be this: The safer, easier, and more functional that biking seems, the more people will do it.