The train in Tuesday's fatal Amtrak crash in Philadelphia was traveling at 106 mph before it derailed.

That was more than double the speed limit at the curve in the tracks, but much slower than the roughly 200 mph that trains in Europe routinely reach. 

Sharp curves are one of the most important factors that make high speeds unsafe on American train tracks, said Vukan Vuchic, an emeritus professor of transportation systems engineering at the University of Pennsylvania.

"The allowed maximum speed in every curve depends on its sharpness, on its radius," Vuchic said. "It has to be larger and larger radius if you want higher and higher speed."

International high-speed rail systems have dedicated tracks with railroad ties specifically designed to prevent the track from sagging as the train passes, which prevents dangerous shaking at high speeds, Vuchic said.

"You sit in the restaurant car and your glass of water or wine is not spilling over," Vuchic said of international high-speed trains. "Here, even in the Northeast Corridor, our best corridor here, sometimes it's really shaking, it's unbelievable."

Vuchic said Amtrak trains also stop frequently, cross roadways at street level in some places in the Northeast Corridor, and sometimes lack the kind of barriers that prevent livestock from wandering onto tracks. Many trains are still without the kind of computer-aided safety system that could have prevented Tuesday's crash.

Amtrak, commuter rail systems and a group called the Northeast Corridor Commission in recent years all have proposed replacing sections of of train track and removing bottlenecks to allow for faster, safer train travel on the East Coast.

These plans haven't progressed because transit agencies don't have the money, said Greg Krykewycz, manager of the Office of Transit, Bicycle, and Pedestrian Planning at the Delaware Valley Regional Planning Commission.

"To acquire land, to change the alignment of the track, is a lot more expensive than it would have been when the line was originally constructed," Krykewycz said. "These are dense urban neighborhoods and you have to buy a lot of private property at fair market value, and it's a very expensive undertaking."

Rachelle Alterman, a lawyer and international land use expert at the Israel Institute of Technology in Haifa, said compulsory acquisition of land, known as eminent domain in the United States, is a complex process requiring intense negotiations in any developed country.

There may be an added element of difficulty in acquiring land in the U.S., though.

"Americans are a little more litigious in land issues, a little more eager and willing to take controversies to the courts over land issues," Alterman said.

Still, Alterman attributes the lack of high-speed rail in the United States to cultural factors and voter priorities more than land use law.

"It may be 'easier' for a government entity to acquire the land for rail in Europe for things like high speed rail because there more of a culture of acceptance of the investment and a longer tradition using it," said Robert Puentes, director of the Metropolitan Infrastructure Initiative and Senior Fellow at the Washington, D.C.-based think tank Brookings Institution.

The Amtrak derailment in Philadelphia has brought conversations about infrastructure upgrades and funding for mass transit to the forefront in Washington once again, though lawmakers still appear resistant to increasing funds.