“Sometimes, it’s only a matter of a particular track cleaner not doing their job,” said Robert M. Corrigan, a rodentologist who led the study.

Still, the city did offer some practical advice. Nothing quite excites a rat like a station’s “refuse room,” a storage space for bags of garbage waiting to be hauled away. For rodents, the room is “a restaurant,” as Dr. Corrigan called it, and he recommended that the transportation authority install poison bait in the rooms for a more surgical strike. (Currently, the authority places poison only on the tracks.)

Entrances to the rooms should be guarded, Dr. Corrigan said, so rats cannot reach the food. He also suggested that transit officials invest in more high-tech trapping systems, although he said budget concerns would probably stymie such plans.

Indeed, a spokesman for the transportation authority said Tuesday that the agency would “need to evaluate the costs associated with implementation moving forward.”

Dr. Corrigan said he remained optimistic that a better system of prevention could be in place within the next two years.

It seems that rats like to hang out in stations, but not on trains. Perhaps for good reason: In 1976, an academic study concluded that “rats with high blood pressure should not ride the subways too often or too long: the stress of noise, vibration, and crowding may kill some of them before their time.”