The 100th annniversary of the first Brooklyn-to-Manhattan subway line last month was an occasion for nostalgia, but also for rebukes from users of mass transit in the region who aren't convinced there have been any improvements to our rail system in that century.

There have been upgrades, but there is so much more to do. Friday night's sideswipe incident between two Long Island Rail Road trains east of Jamaica station reminded us again of the system's vulnerable nature.

In New York City in the 1970s and 1980s, the subway system was dilapidated, graffiti-covered and menacing. On Long Island, trains, tracks and signals were aging and under-maintained.

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The Metropolitan Transportation Authority has made significant improvements in the past three decades. Service has increased and equipment is more reliable. LIRR ridership has grown 19 percent in 30 years. Subway ridership has returned to levels unseen since World War II.

What allowed the MTA resurgence was largely the adoption of five-year capital improvement plans, starting in 1982, plunging more than $100 billion into the system. This approach to major maintenance and improvements has paid off. On-time performance has improved on the LIRR, train service has expanded and the facilities and equipment are cleaner and more comfortable.

But funding for every five-year cycle is a battle. The cities and counties served by the MTA, as well as the state, have failed to create a consistent stream of money to buttress this mighty engine of economic vitality.

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The capital plan for 2010-14 had to be divided into two funding periods because money could only be found initially to fund the first two years of work. In the end, the funding gap was closed only through a mishmash of "efficiencies," refinancing, the increase of MTA debt to $34 billion and reduced ambitions.

Now the MTA is again casting about for lifelines as it tries to fund $32 billion of needs for its 2015-19 plan. Experts and officials say the "one-shot" sources of money that past chairmen Jay Walder and Joseph Lhota found for the last plan are, well, shot. The MTA has about $18 billion covered -- with a gap of about $14 billion to fill.

It's easy to look at such a big number and assume it's an opening salvo, inflated so that it can be safely trimmed. Yet, transportation advocates say the opposite is the case. It can easily be argued that the MTA needs $40 billion to $50 billion to modernize and maintain the system, but there's no prospect of getting that much money.

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MTA capital funding is crucial to Long Island, for the 279,000 workers who commute to the city, for the about $50 billion in economic activity they engender, and for the economic vitality of the greater metropolis and inter-island transportation. The East Side Access project that would send LIRR trains into Grand Central Terminal is not fully funded. New rail cars are needed, and so is a new signal system for positive train control, a major safety initiative. The double-track project on the Ronkonkoma line must be completed. The Oyster Bay line needs to be modernized. And for those who drive, the Midtown Tunnel needs new monitoring systems, wall tiles and lighting.

Fares and tolls provide some of the money and should continue to rise at a moderate rate, but those can only fund so much, and mostly go to the MTA's $14 billion annual operating budget.

Scrambling every five years to find funding sources for such crucial investments is bad management by our elected officials. And it has led to the aggravating jumble of hidden taxes and fees we have now that hardly any taxpayer fully understands. It's time for the city, region, state and MTA to create a consistent stream of cash for the capital plans. The MTA has a big responsibility to save money by eliminating expensive work rules and raising more revenue through advertising, public-private partnerships, real estate and other initiatives.

We can't let our investment in world-class transportation falter, because we know what happens when it does. We've seen that movie before.