Why the cold put your morning commute on ice

Did you spend a frigid Tuesday morning on a train platform waiting for a delayed ride to work? It turns out the cold can make things as uncomfortable for an old public transportation network as it does for your fingers and nose.

Temperatures plummeted from the low 30-degree range Monday to as low as 12 degrees Tuesday morning. A precipitous drop like that worsens the problems cold causes on public transportation, and that was further exacerbated because Tuesday was the first really cold day of the season.

"Older vehicles, it hits you hard when you have these big drops, but it hits you really hard when you have that first one," said Jeff Knueppel, SEPTA's General Manager.

SEPTA did prepare for the sudden temperature drop, but completely anticipating where problems would arise is impossible. Exasperated passengers who waited nearly an hour for a ride weren't the only ones out in the cold, officials said. SEPTA deployed Tuesday morning a small horde of track people, power people, vehicle equipment people and transportation managers to try to respond to problems.

SEPTA prepared for the cold weather, officials said, but that didn't stop the freeze from freezing the system. According to SEPTA's Twitter account, the entire Regional Rail system experienced delays up to 40 minutes long. Switches froze. Trains and trolleys had to slow down. Brake lines were at risk of seizing up.

Sudden temperature drops affect infrastructure and vehicles in so many ways. Metal contracts in cold like anything else, and on rail controlled by Amtrak between University City and Philadelphia International Airport, that contraction actually caused a gap in the tracks Tuesday. Even if the gap is just an inch, that's wide enough to set off a stop signal, and trains have to be moved slowly over the gap until repairs or rerouting can happen.

Trolleys and trains were running no faster than 50 mph Tuesday morning, SEPTA officials said, due to the risk of a train pulling down catenary wires. The cold changes the wires' tension, and a vehicle's pantograph (that overhead pole that connects an electrical vehicle to the wires) can pull the infrastructure down if its going too fast.

Most of the vehicles' systems, like brakes and doors, uses air to operate. If there's moisture in the lines that freezes, that can interrupt the flow of air and cause systems to seize up. The default setting for train brakes is "on," so when there are brake problems the vehicle automatically stops. There were at least 10 incidents of freezing in air lines causing problems on buses and trolleys Tuesday morning.

All these circumstances conspired to slow down the system, and a domino effect meant trains arrived at stations with an overload of people waiting for their rides. Trains heading to Philadelphia filled up and in some cases were overloaded with passengers, causing them to skip stations closer to the city. SEPTA officials insisted Tuesday that trains would not bypass a stop in order to keep to its schedule. If your train passed you by, it was because there was no room for more passengers, they said.

"It's not about schedule," said Ron Hopkins, SEPTA's assistant general manager and chief operations officer. "It's about trying to provide service to all the passengers that are waiting. If there's room we're stopping."