Meshed Wi-Fi technology is getting a boost from the railroads, with a network going up along a 42-mile Southern California railway that's the second-most-traveled line in the United States.

The network is for security, not passenger use. It presently covers 10 miles of the Coaster route between San Diego and Oceanside and is the first of its kind in commercial production on a railway, says North County Transit District CIO Kirk Talbott. It will cover the remaining track by year's end.

The network was built using a $170,000 Department of Homeland Security grant, and Talbott estimates it will cost another $300,000 to $400,000 to finish.

Public transit systems have become a particular focus for security agencies, particularly after the 2005 bombings of three London Underground subway trains. London's network of cameras didn't prevent the blasts, which killed more than 50, but they provided evidence that led to the bombers' arrests.

But railways are a challenge for network builders because they often traverse remote areas, require a continuous "tunnel" of coverage and connectivity, and must keep pace with trains moving at high speeds.

The network was installed by Datel Systems using Strix Systems mesh equipment, consisting of a series of solar-powered nodes spaced about seven-tenths of a mile apart and connected wirelessly to fiber-optic cable at the train stations. So far, the transit agency has mounted two video cameras on the line: one at a bridge across the Agua Hedionda Lagoon, another at an undisclosed site plagued by vandalism.

The Coaster averages 48 passenger and two freight trains a day, carrying 1.5 million passengers a year, and passes through Camp Pendleton, one of the country's largest Marine bases, making it a very visible project. The Strix system provides throughput of 17 to 20 Mbps along the line, making possible closed-circuit TV transmission from inside the cars.

Older rail lines, which typically don't have fiber laid to the stations, will be harder to cover with wireless networks. Nevertheless, Talbott expects such networks to spread, once lines like the Coaster prove what can be done.