The split between the lettered and numbered subway lines predates the creation of the Metropolitan Transportation Authority. Two private companies, the Interborough Rapid Transit Company and the Brooklyn Rapid Transit Company, ran the two divisions as separate subways until 1940, when the city purchased both and merged them into one system. But the same trains cannot run on both line divisions because the company that owned the lettered lines dug tunnels wider than those on the numbered lines.

The varied history of the two divisions still shows itself today in the competition for capital from the MTA, which modernizes only one division at a time. After two decades of using trains that break down more often than those on the numbered lines, the lettered lines may finally be gaining the technological edge.

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The numbered lines have historically been the first to receive technical upgrades from the MTA. While the numbered lines received new cars about five years ago, the C and the E lines are still equipped with trains that date back to 1964, a Transit Authority spokesman, Charles Seaton, said. A subway car is built to last about 35 years, but Mr. Seaton said the MTA’s maintenance procedures have extended their natural shelf lives.

Double the size of Astroland, the multitiered park will include 21 rides, a hotel, a manmade canal for boat rides, a glass-encased atrium and commercial space.

Abandoning the machines, which cost between $15 million and $20 million apiece, may prove more efficient and cost-effective for project contractors than hauling them out through the holes they carve through soil and rock. If left underground, the machines would be turned away from the tunnels and then retired.

“We could leave it underground,” president of the Capital Construction Co. at the Metropolitan Transportation Authority, Mysore Nagaraja, said yesterday, referring to the tunnel boring machine that is scheduled to break ground on the Second Avenue subway project in 2008. The two tunnels that will run along Second Avenue, and perhaps the final resting place of the machine that creates them, will lie about 62 feet below ground, an MTA spokesman said.

“It’s a huge assembly. It’s not a simple machine, something you can hold. But how the contractor wants to use the machine is really up to him,” Mr. Nagaraja said. The contractor for the Second Avenue subway project will be announced today by MTA officials.

For the the third day in a row, the number of stations with at least one elevator out of commission reached double digits, according to the Disabled Riders Coalition, which called the outages a “citywide epidemic.”

Among those not working was one of the elevators at the Yankee Stadium stop – 161st St. and River Ave. — in the Bronx, a major hub for trains on the B, D and 4 lines.

“These outages are leaving disabled riders stranded,” said coalition coordinator Michael Harris.

The signs, which will get train locations from a network of onboard and track-side computers, will take the guessing game out of using the subways, officials said. Upgraded sound systems also have been installed in the stations on the Canarsie line.

“With the introduction of this new system, garbled subway messages are on their way to becoming a thing of the past along the L line and eventually the entire system,” Metropolitan Transportation Authority CEO Elliot Sander said.