The study from Northeastern University looked at the impact of new transit stations in 42 neighborhoods in 12 metropolitan areas. Many of them showed signs of gentrification, including rent increases, rise in car ownership and rise in income, according to this summary from Next American City.
"These facts seem to demonstrate that the arrival of a new transit station will result in significant changes in the type of people who inhabit the neighborhood. Of the cities studied, those with light rail were the most likely to see major changes. The evidence related to increases in housing costs, owner-occupation, and automobile ownership seems to suggest that the population of these neighborhoods becomes wealthier over time. (This does not necessarily mean the poorer residents of the neighborhood have moved out; growing populations could mean simply a higher density over time. This study makes an assumption this this transition is happening.) Interestingly, this does not necessarily mean more white: Only half of new transit neighborhoods saw an increase in their white population relative to the region as a whole, with the other half seeing a drop."