1. Ridesharing has a strong cultural and social aspect to it. The largest group of ridesharers are family members, co-workers and neighbors. Certain groups, namely Hispanic-Americans, share a large proportion of rides in the US.
2. Changes in Disposable Personal Income, whether due to higher gasoline prices, lower overall earnings or an economic downturn, appear to have a significant effect on aggregate rideshare participation. Rideshare surveys tend to support this finding, with participants often listing cost savings as one of the three main reasons for sharing rides.
3. At an aggregate level, rideshare participation appears to be higher in low density metropolitan areas, but the reasons for this are not entirely clear. Intuitively, ridesharing requires at least some density of riders with similar origins and destinations in order to work. However, higher densities are often accompanied by larger and more interconnected transit systems that may compete for rideshare participants. For lower density metropolitan areas, ridesharing may function as a type of small vehicle transit.
4. Ridesharing and transit are likely complements and substitutes. The international analysis of transit share and rideshare participation suggest (at a very high level) a potential substitution between the two modes, however the metropolitan analysis did not show any significant trade-off between transit share and ridesharing in the US context. There is evidence from San Francisco that people who choose to rideshare previously rode transit, suggesting that the two modes are substitutes. On the opposite side, evidence from Seattle, San Francisco & Washington DC suggest that when passengers cannot find an appropriate ride-match, they rely on transit services to reach their desired destination, suggesting that the two modes complement one another.