Clean up the subways.

Talk of improvements on the rails often centers around century-old signals, tracks and tunnels that need upgrades, and a system that seems to be breaking under its own weight and age. In that context, trash on the tracks might not seem like a top priority.

Monday morning’s rush hour proved otherwise.

At around 7:30 a.m., an underground track fire started near the 145th Street stop at St. Nicholas Avenue. Nine people suffered minor injuries. The fire, caused by garbage on the tracks, led to suspended service on the B and C lines, and delays on the A and D lines. That disruption cascaded through other parts of the system, leading to massive overcrowding in stations and trains on the 1 line. It was a mess.

Earlier this year, the MTA tested portable vacuums that could hose up trash that riders discard on the tracks. Those vacuums, the MTA said, reduced trash by 51 percent in the test areas. Track fires, the MTA said, fell from 75 in January to 53 in June.

In a six-point plan announced in May, the MTA said it would put two vacuums on the Eighth Avenue subway lines, which the A train travels, full time. The agency said it would focus on a corridor up to 125th Street. Apparently, the vacuums didn’t get as far north as 145th Street recently.

The MTA said a review of Monday’s incident is underway, and there are plenty of questions to answer. Could passengers have been removed from the sweltering trains stopped in the tunnels sooner? Could the crowds that were diverted to the 1 train have been managed better? And, in what is an ongoing refrain, how can the MTA improve communication with its riders?

The MTA said Monday it would put 12 portable vacuums in service to clean up the system’s 670 miles of track used for daily service. And the MTA should use the equipment effectively and find new ways to strengthen and expand its program, known as Track Sweep. Pizza rat can’t do the job alone.

On this issue, however, straphangers can do their part, too. Public service reminder: Please, don’t throw anything onto the tracks or leave trash on the platforms.