NEWARK — Many NJ Transit riders scoffed at the explanation for systemwide 30-minute delays on Monday: "slippery rails."

But it's a real issue, and it will cause delays for a second day on Tuesday. It's also a problem for SEPTA, PATCO, Metro-North, and LIRR trains as well.

NJ Transit spokesman Jim Smith said earlier that autumn leaves leave an oily residue on tracks this time of year — "what we call 'slippery rail' prevents the trains from getting up to full speed. And this can cause delays."

The problem is compounded by rain.

When the trains roll over leaves, they get pulverized — leaving the residue behind. But Smith said using AquaTrack diesel-powered engines on a flatbed rail car, "the operator can utilize these two pressure pump units to dispense water, up to 20,000 pounds per square inch, directly on top of the rail."

The most challenging areas for crews are the hilly areas around Glen Ridge and Summit stations, where AquaTrack hits the rails overnight and during the midday.

NJ Transit has had its share of delayed trains in the past week, especially in the afternoon, unrelated to ongoing Positive Train Control installation.

Democratic candidate for Congress Mikie Sherill was so concerned about the effect of potential delayed trains that she told volunteers to suggest voters cast their ballots in the morning so any NJ Transit delay would not keep them from the polls, according to video posted on NJ.com.

Previous reporting by Joe Cutter was used in this report.