Monday is the last day to register to vote in Pennsylvania's May 16 primary.

Off-year primaries are usually the lowest turnout election in the four-year cycle, and Franklin & Marshall College political science professor Terry Madonna said he doesn't expect this time around to be any different.

"Typically turnout in odd-numbered years in primaries is very, very low," Madonna said. "We might be talking about 20 percent — even lower in some places than 20 percent of the registered voters."

Philadelphia has a district attorney race. Statewide, it's mostly judicial contests.

Candidates in years like this don't usually push large voter registration drives, Madonna said.

"Normally what has to happen is you need organizational drive efforts by the candidates and the parties," he said. "And the ad campaigns of the candidates also spur voter registration."

In Philadelphia, controversy over indicted District Attorney Seth Williams could spur some additional interest in the race to replace him.