A California security study says a key U.S. rail link is vulnerable to terrorist attack. The study of a busy rail line near Los Angeles says a shutdown would harm the U.S. economy. The rail network south and east of the city is called the Alameda Corridor East, and it links the joint ports of Los Angeles and Long Beach to rail lines leading to Chicago and other parts of the country.

More than $100 billion in goods moves through the corridor each year. U.S. officials have designated the link, and 60,000 kilometers of other U.S. rail lines, as strategically important national assets. The lines ensure that the military can quickly move heavy equipment, such as armored vehicles, in the event of an emergency.

Christopher Becker heads the Orange North American Trade Rail Access Corridor, the public agency that oversees this California rail link. He says a 10-day disruption would cost more than $4 billion, and that other lines like this one are at risk throughout the country.

"Right now, across America, railroad tracks really are vulnerable. It's almost impossible to protect them all," says Mr. Becker. "And what our study is saying is that these vital strategic rail corridors that provide a lot of America's economic well-being need to have extra protection and extra vigilance by everybody in watching and monitoring."

A 10-day shutdown of West Coast U.S. ports last year foreshadowed the problems that would be encountered in a shutdown of the rail lines. The port closure, caused by a labor dispute, left automakers unable to get car parts and restaurant owners unable to get imported food and produce.

"The West Coast saw about $1 billion a day in value, and we saw that last for 10 days," says Wally Baker, senior vice president of the Los Angeles County Economic Development Corporation. "We also saw a 30-day, maybe longer, rewinding period." He says a terrorist attack on the rail lines could potentially have a greater impact because the railways carry U.S. goods between Southern California, a $300 billion market, and other parts of the country.

"We're looking at a terrorist incident, so then you're dealing with something that's far worse, because not only do you have something like a $415 million a day impact, you're not just impacting international trade now; you're impacting domestic and international trade," Mr. Baker says.

The report's authors say police and firefighters often lack the training to deal with a derailment or other problems on the rail lines. Security analyst Elsa Lee, who contributed to the report, wants federal officials to conduct a risk assessment of the Los Angeles rail corridor.

She says there is a clear threat to the rail system from international groups like al-Qaeda, which have threatened to strike key parts of the U.S. infrastructure. "We believe that the threat of terrorism is real and is not perceived. That's based on a number of factors. That's based on declared threats from terrorist groups," says Ms. Lee. "It's based on terrorist acts that have taken place against rail systems overseas, and we believe that when terrorists make threats against our rail system, they have to be taking very seriously."

She says there is also a threat from domestic terrorists, such as the radical environmental group Earth Liberation Front.

The report notes there are 230,000 kilometers of rail lines in the United States and says security needs to be improved along key transit points. The report's authors suggest that a portion of customs revenues collected at the ports be used to finance the improvements.