Falling ridership at the PATCO commuter rail line and fewer vehicles across toll bridges are a result of many factors, Delaware River Port Authority officials said Monday.

The Inquirer reported last week that PATCO ridership was down 1.7 percent for the first eight months of 2013, after a decade of steady growth. And vehicle traffic on the four DRPA toll bridges is also down this year, continuing a six-year slide.

In August, PATCO ridership dropped 4 percent from the same month the previous year. The month was especially difficult for the commuter line, with widespread failures of escalators, and dozens of canceled and delayed trains that angered riders.

DRPA officials said traffic and ridership were "a function of a number of factors, [and] three stand out: the economy, gas prices, and toll/fare rates."

They also released September ridership numbers for PATCO, which showed a 1.1 percent increase from the monthly ridership during the same month a year earlier.

"The trend for PATCO ridership has been increasing since 2003," the DRPA said in a statement. "This year, 2013, is projected to be the third-highest year of ridership for PATCO since 2001, with projected ridership of approximately 10,461,000, a reduction of 1.06 percent from 2012."

Though ridership is expected to be lower this year, it is still expected to be about 91,000 riders, or 1 percent higher, than PATCO anticipated in its 2013 budget, the statement noted.

Falling gas prices were cited as a possible reason for falling ridership, because "historically, when gas prices increase, PATCO ridership increases and declines when prices fall."

"Unemployment, underemployment, part-time vs. full-time employment, telecommuting, less discretionary consumer spending, reduced traffic to the Jersey Shore, [the economy], DRPA/PATCO capital projects, the length of playoff seasons for the regional sports teams, and weather are some of the factors," the agency said, "in explaining lower ridership and bridge crossing numbers."