The gap problem now facing the Long Island Rail Road was set in motion more than 150 years ago, as the fledgling railroad pushed east from Jamaica, building stations on donated land.

In the early days of train travel, passengers climbed onto steam trains from ground level, mounting stairs built into the sides of the cars.

Towns and villages that wanted LIRR stations provided land to the railroad. It posed no problem then that many of these parcels sat on curved sections of track.

Many years later, however, those curves would create some of the worst gaps on the railroad -- gaps the LIRR now is trying to narrow.

In the beginning

In the 1830s, as the newly incorporated LIRR expanded to Hicksville and Farmingdale, it used whatever land local officials made available to build stations, said LIRR spokeswoman Susan McGowan.

Forty percent of the LIRR's stations were built on curved sections of track.

"It may have started 150 years ago as a little, tiny platform where a conductor came down and put a box on the ground ... and it has now turned into Hicksville station," said Metro-North Commuter Railroad spokeswoman Marjorie Anders.

Those curves proved problematic when the railroad began raising platforms to the height of train doors in the early 1900s -- a practice that expanded in the '50s and '60s.

Engineers faced a new dilemma: If they set tracks too close to these raised platforms, trains might plow into the platforms. But if they set the tracks too far away, passengers risked falling into the gap they had created.

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Gap standards

Another century-old factor contributing to the size of platform gaps emerged when the LIRR began offering service to the newly built Penn Station. To use Penn Station, the LIRR had to meet clearance requirements -- still effective today -- that restrict train width to no more than 10 feet.

Narrower trains mean wider gaps.

The railroad industry developed standards for the minimum clearance needed for freight trains -- which are wider than passenger trains -- to pass safely. This standard, mandated by New York state railroad law, is 5 feet, 7 inches from the center of the tracks to the platform.

Metro-North uses this measurement as its internal standard. The LIRR, however, sets its tracks an extra inch farther from the platform, a practice dating to 1963. LIRR officials, who are now reconsidering the practice, said they did not know why it was adopted.

These internal standards combined with the widths of the train can be used to calculate gap sizes.

Metro-North, which does not use Penn Station, has wider trains than the LIRR. As a result, Metro-North's standard minimum gap is as small as 5 inches, while the LIRR's is 8 inches.

Government oversight agencies have never mandated a maximum width for platform gaps that they could enforce. Instead, they have focused almost exclusively on allowing enough room for trains to pass through stations.

The only law setting a maximum gap is the federal Americans with Disabilities Act, which calls for no more than 3 inches between the train and the platform at stations built after 1991.

But federal officials admit that a 3-inch gap is impossible for most commuter rails to achieve because it doesn't allow enough space for trains to pass.

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Many commuter rails end up complying with the ADA through an exception in that law, which allows the use of bridge plates -- metal ramps that extend manually from train doors to platforms.

The U.S. Department of Transportation is considering new ADA regulations that would limit gaps at new stations to 10 inches on straight platforms and 13 inches on curved ones.

Platform problems

Curved platforms require extra space for trains to pass safely. In other words, they need a bigger gap.

Think of a square inside a circle. The corners are close to the circle's edge, while the straight sides are farther away. That's what a straight-sided train car looks like next to a curved platform. When laying track, engineers must leave enough space for each car's corners to pass unscathed.

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When a platform curves the other way, engineers must ensure that the middle of the car doesn't scrape the platform.

An industry standard adopted in 1913 barred the construction of stations on sharp curves. The LIRR's worst gaps are on curved platforms that predate that rule: 151/2 inches at Flatbush and 14 inches at Syosset.

Of the LIRR's 125 stations, 50 are on a curve, McGowan said. The railroad has 264 platforms, of which 150 are curved.

Of course, gaps occur on straight platforms, too. At straight platforms, obstructions on the rails -- such as a grade crossings, where streets cross the tracks -- can force engineers to set tracks farther away from the platforms of nearby stations.

Ragged platform edges can worsen gaps on both curved and straight platforms. This factor contributed to a 133/4-inch gap on the straight platform at Shea Stadium, according to LIRR officials. In August, maintenance crews shifted the track up to 41/2 inches closer to the platform, the railroad said.

Vertical gaps

While much attention has focused on horizontal gaps, the vertical distance between a train door and the platform can also pose a problem, tripping up passengers and increasing the risk of falls. A Newsday measurement at Port Jefferson station in October, for example, found a 15-inch horizontal gap compounded by a vertical gap of 6 inches.

Settling of tracks or platforms causes some of the worst vertical gaps, forcing riders to step up or down when they get on or off the train.

The following are other factors affecting vertical gaps:

On a banked curve, one side of the train sits higher than the other, tipping the door above or below the surface of the platform.

Train wheels wear down by 2 inches in diameter before they must be replaced. Trains ride high on new wheels, then sink as the wheels age.

A train's suspension system, which uses air bags, also varies by a couple of inches, depending on how much the bags are inflated.