It would be the world's longest highway tunnel, running more than 26 kilometers under the west end of Long Island Sound. The cost is estimated at $10 billion - and it would not cost taxpayers a dime. A developer wants to build the tunnel with private money, recouping his costs by charging drivers $25 each way and by selling advertising. Developer Vincent Polimeni says the tunnel between Oyster Bay and Rye on the New York mainland would let travelers going between Long Island and New England avoid crowded New York City highways and help alleviate traffic congestion. While not expected to be completed before 2025, the proposal received renewed attention this past week when a state Senate committee held a hearing. Polimeni acknowledges his idea was initially met with "smirks and skepticism." But he added: "The more people looked at the plan, the larger circle of intrigued citizens who said `tell me more.' "