But Amtrak has proven to be more sensitive to oil prices' fluctuations than regional rail systems. Last week SEPTA officials said they've seen a slight drop in ridership in recent months likely linked to the price at the pump, but said it wasn't enough to cause concern. That mirrors ridership trend research that found demand for commuter rail service will eventually change if gas prices go up or down over a long period of time, but stays fairly inelastic in the short term. A 2014 study found that a 10 percent increase in gas prices resulted in only a 1 percent shift in ridership on commuter rail, said Hiroyuki Iseki, a University of Maryland assistant professor who was an author of a 2014 study on the topic.