regarded as light rail, but considered distinctly as streetcars or trams. However, the requirement for saying that a rail line is "separated" can be quite minimal – sometimes just with concrete "buttons" to discourage automobile drivers from getting onto the tracks. There is a significant difference in cost between these different classes of light rail transit. The traditional style is often less expensive by a factor of two or more. Despite the increased cost, the more modern variation (which can be considered as "heavier" than old streetcar systems, even though it's called light rail) is the dominant form of new urban rail transit in the United States. The Federal Transit Administration helps to fund many projects, but as of 2004, the rules to determine which projects will be funded are unfavorable toward the simpler streetcar systems (partly because the vehicles tend to be somewhat slower). Some places in the country have set about building the less expensive streetcar lines themselves or with only minimal federal support. Most of these lines have been "heritage" railways, using refurbished or replica streetcars harkening back to the first half of the 20th century. However, a few, such as the Portland Streetcar, use modern vehicles. There is a growing desire to push the Federal Transit Administration to help fund these startup lines as well. Light rail is generally powered by electricity, usually by means of overhead wires, but sometimes by a live rail, also called third rail (a high voltage bar alongside the track), requiring safety measures and warnings to the public not to touch it. In some cases, particularly when initial funds are limited, diesel-powered versions have been used, but it is not a preferred option. Some systems, such as AirTrain JFK in New York City, are automatic, dispensing with the need for a driver; however, such systems are not what is generally thought of as light rail, crossing over into rapid transit. Automatic operation is more common in smaller people mover systems than in light rail systems, where the possibility of grade crossings and street running make driverless operation of the latter inappropriate. Very light rail or ultra light rail Very light rail or ultra light rail is a term for light rail with more modest initial requirements than typical light rail. Parry People Mover which is grade-separated, low passenger capacity (maximum 35 standing) powered by LPG with no overhead lines, has been