[This post has been updated]

For Virginia Railway Express and other rail agencies fall isn't the best of times.

It’s the season when millions of fallen leaves can cause service delays for railroads and subways across the country as residue on the rails necessitates speed restrictions for safety reasons. Fallen leaves get crushed against rails by steel train wheels, depositing a residue that decreases friction, which can cause slippage.

On Thursday, VRE canceled some service and Manassas Line riders endured delays of more than an hour minutes as trains slowed because of the potential danger. Some Manassas Line passengers reported that one train, VRE 331, didn’t move for at least 45 minutes. The conductor suggested passengers find alternate transport from the Backlick Road station. VRE’s system map showed the train running 55 minutes behind schedule at one point, with four trains bunched between Burke Center and Alexandria. Conditions improved once trains cleared the crest of a hill north of Rolling Road. .

Slippery rail also has shown up this season as a cause of delays for the Maryland Area Regional Commuter train service.

How do railroads combat the problem?

The Southeastern Pennsylvania Transportation Authority, which serves Philadelphia and surrounding counties, says that it has an “aggressive maintenance program,” including pressure-washing rails, to combat the problem. Here in Washington Metro crews trim leaves and other vegetation. Metro also vacuums leaves from the rails.

Metro has 25 mph “speed restrictions in place as trains arrive at eight stations as part of our effort to prevent flat spots,” said Metro chief spokesman Dan Stessel.

Metro has also said that slippery rails can lead to flat spots on train wheels, due to the repeated need for braking, Metro said. That condition requires trains to be removed from service for wheel repairs.

However, Stessel said the transit authority has seen improvements this year.

“Definitely better than last year, largely due to tree trimming efforts,” he said.