The old adage about making sure you have a full tank of gas when you arrive in Vegas to ensure you can get home may have a new wrinkle.

Two plans for a high-speed rail line connecting Las Vegas to Southern California are being proposed by competing factions that both believe the shorter travel time and ability to lengthen the festivities will lure enough drivers off Interstate 15 to support such projects.

Las Vegas-based DesertXpress last month pitched the latest details of a $4 billion plan for a steel-wheels-on-rail train that can travel up to 150 mph and would connect Las Vegas to California’s planned north-south, high-speed rail network.

Executives at DesertXpress, whose plan has been in the works for seven years, say the privately funded project could break ground as early as March and would take about four years to build.

The catch is that the southern terminus of the 200-mile, 84-minute route is Victorville, Calif., about an 80-mile drive northeast of downtown Los Angeles, because the Cajon Pass connecting Los Angeles to Southern California’s high desert is too steep for traditional rail.

Riders, who would pay about $50 for a one-way ticket on the line, would still have to drive between Los Angeles and Victorville until the completion of the high-speed California network, which would shorten the commute between Victorville and Los Angeles to about 45 minutes.

The California project is expected to break ground as soon as 2011 and is estimated to be completed around 2023.

The second major proposal, which is being pitched by Los Angeles-based American Magline Group and backed by the California-Nevada Super Speed Train Commission, plays even further into Las Vegas’ "wow factor" sensibilities: a 270-mile magnetic-levitation line in which the train literally hovers slightly above the tracks, travels at a top speed of more than 300 mph and connects Las Vegas to Anaheim, Calif., in just 80 minutes.

That proposal, however, involves a far bigger gamble: a price ranging from its proponents’ estimate of about $12 billion to a more pessimistic estimate from the Desert-Xpress contingent of as much as $40 billion.

Either way, a high-speed rail route, which would be the first train service between Los Angeles and Las Vegas since Amtrak’s Desert Wind line was discontinued in 1997, would pull millions of cars each year off of a drive that takes almost five hours in the best conditions and can take almost twice that long with weekend traffic.

Last year, Las Vegas attracted 37.5 million visitors, with about 38,000 cars crossing the California-Nevada border at I-15 per day, down from 39.2 million visitors and about 40,000 daily cars in 2007, according to the Las Vegas Convention and Visitors Authority.

Last year, 24% of the city’s approximately 40 million visitors came from Southern California, down from 29% in 2005.