That means when a train pulls into a station with a sick passenger, the agent cannot escort the rider off. Instead, the train crew often must remain until medical help arrives. Sick passengers caused 2,747 significant delays on weekdays in October, transit records show — a new problem nearly every 10 minutes that might have been minimized if a transit worker not on the train had been available to help.

Instead, tens of thousands were delayed while agents stood by in station booths or on mezzanines.

Riders looking for real-time information about delays or diversions generally have to rely on announcements over spotty public address systems. To ask a station agent, passengers have to go to the booths outside the turnstiles because the agents generally do not go to the platforms.

Among the most critical short-term needs for reducing delays is for workers who can manage station chokepoints. With twice as many daily riders as 25 years ago, crowding is the immediate cause of thousands of delays.

Once a train’s “dwell time” in a station lasts longer than 30 seconds, it starts to fall behind schedule. Delays cascade backward. Even the most advanced signals cannot push service through stations where trains are held up by surges of riders.

The system has 129 “platform controllers” with crowd-control duties, and they are often outnumbered. “We’re popping off at the hinges,” said Derick Echevarria, a vice president with Local 100 of the Transport Workers Union.

Since November, a cadre of 40 clerks have joined a one-year pilot project tentatively called “Wayfinders.” They will be able to escort sick passengers from trains, and will carry tablets or radios to provide information.