By JULIET WILLIAMS
SACRAMENTO, Calif. (AP) _ Travelers easily whiz from city to city on high-speed trains in many parts of South America, Asia and Europe. Since the first high-speed lines began operating more than 50 years ago in Japan, they have become an essential part of transportation worldwide.

Yet the U.S. has never built a single mile of high-speed rail, which is generally defined as accommodating trains that go at least 200 mph. And proposals to do so have been thwarted for decades.

So what’s holding America back?

For starters, a much larger land mass, longer distances between major cities and the high cost of construction. Other factors include efficient air travel, relatively low prices for gasoline and a car-based culture.

“The challenge in America is the scale of America,” said Robert Eckels, chief executive of the Texas Central High Speed Railway, a private venture that is planning a bullet train between Dallas and Houston.

In recent decades, political pressure against bullet trains has come from conservatives who argue that such systems should acquire private financial backing and prove that their operations will at minimum be cost-neutral. It’s a burden state and federal governments do not place on other huge transportation projects such as freeways and airports.

For now, the best the country can do is Amtrak’s Acela, which reaches speeds up to 150 mph on a busy route between Washington and Boston.

In an effort to jump-start high-speed rail, the Obama administration in 2009 awarded $7 billion for projects in California, Florida and Wisconsin. Republican governors in Florida and Wisconsin rejected the funding and backed out of high-speed rail plans, sending more of those dollars to California.

The list of other proposals for faster-speed rail includes: linking Las Vegas with greater Los Angeles; Chicago with St. Louis; Harrisburg, Pennsylvania, with Pittsburgh; Oklahoma City with Tulsa; and upgrading track on a medium-speed line between Miami and Orlando.

Despite the political resistance and financial hurdles, two projects have moved beyond the conceptual phase. One is California’s $68 billion plan for a high-speed rail network connecting Northern and Southern California. The other is the privately financed plan in central Texas.

In California, voters approved nearly $10 billion in bonds in 2008 to start construction of a 520-mile network, but the project has been beset by years of legal and political infighting. Construction originally scheduled to begin in the Central Valley in spring 2013 is finally underway, but the state’s long-term financing plan relies heavily on federal money that is unlikely to materialize in a Republican-controlled Congress.

Democratic Gov. Jerry Brown remains a strong supporter, negotiating a dedicated funding stream for the bullet train through a separate program that raises money from businesses as part of an effort to reduce greenhouse gas emissions.

“There are some people in California who think of high-speed rail as a mysterious, very expensive, exotic technology,” Brown told reporters last month as the prime minister of Japan, Shinzo Abe, demonstrated Japanese train technology in California.

The Texas project has received much less publicity than California’s, yet it could become the nation’s first operating bullet train line.

A private company, the Texas Central High Speed Railway, is soliciting $10 billion to $12 billion to build a 240-mile track that would whisk travelers between Houston and the Dallas-Fort Worth area in 90 minutes or less. That compares with a one-hour flight, plus parking and security clearance time for air travel, or a four-hour drive, which is forecast to grow to 61/2 hours by 2035 if no alternatives emerge.

Eckels said the company was able to “cherry-pick the best route,” allowing a much smaller scale project than that in California, with known ridership and fewer political entities to balance. Construction is slated to begin in 2017, with trains expected to start running four years later.

“We’re not having to build a huge political constituency that you would have to do in California or in a Chicago to St. Louis,” he said.

Private-public partnerships in construction may be the best way to mute political criticism as well as kick-start the projects, said Andrew Goetz, a professor and faculty associate at the Intermodal Transportation Institute at the University of Denver who studies high-speed rail.

“I think politically it would address a number of concerns, just from the financial side of it, and provide a lot more stability,” he said.

Yet even the privately financed Texas system is encountering some of the same roadblocks as in California, including upset landowners whose homes and farms lie in the bullet train’s path. Lawmakers who represent those rural areas object to the use of eminent domain.

But the private financing allows the project to avoid some of the intense public scrutiny and endless political interventions to which the California plan has been subjected, including government-set limits on the amount of money that can be offered to property owners.

In California, business leaders in the congested Silicon Valley corridor have become advocates of the bullet train.

Rail proponents argue that American companies would be among the biggest beneficiaries, arguing that the lack of high-speed rail has hurt American competitiveness. The typical U.S. business traveler spends two days of travel to attend one meeting, said Andy Kunz, president and chief executive of the U.S. High Speed Rail Association.

“We’re stuck in traffic for hours. We’re dealing with horrible airlines as it deteriorates,” he said. “The whole country is getting shortchanged by this.”