Slate's Bizbox
explainer: Answers to your questions about the news.

What's a Double-Layer Fence?The latest trend in border protection.

By Daniel Engber
Posted Monday, Sept. 25, 2006, at 6:53 PM ET

Download the MP3 audio version of this story here, or sign up for The Explainer's free daily podcast on iTunes.

The Senate will vote this week on whether to build 698 miles of fencing along the Mexican border. The Secure Fence Act of 2006, which the House has already passed by a wide margin, calls for "at least 2 layers of reinforced fencing, the installation of additional physical barriers, roads, lighting, cameras, and sensors." What's a two-layer fence?

Two fences, separated by about 50 yards. A possible model for the proposed fence sits along what had been a very porous, 10-mile stretch of borderlands near San Diego. The California National Guard helped put up the first layer, which consists of 8-foot-high recycled aluminum landing mats from the Vietnam War. A few years later, Congress provided money for the second layer—a 15-foot mesh fence with an angled top.

Here's how the double-layer fence near San Diego is supposed to work: Border agents patrol the area by driving their vehicles along an all-weather road that runs between the two fences. Any smugglers or illegal immigrants who tried to scale the outer barrier will get slowed down enough for the agents to converge and capture them. The two-layer fence also has stadium lights to make attempted crossings more visible.

The labor union that represents border agents has warned that the space between the fences could be an especially dangerous place to work. Agents patrolling that no-man's land are more vulnerable to rocks and bullets fired from the top of the outer barrier. If the agents do get in trouble, they can escape from side-opening doors on the inner barrier, which are controlled from each agent's vehicle or hand-held radio.

In May, the Senate voted in favor of a different plan to build 370 miles of triple-layer fencing along the southwest border. A triple-layer scheme includes a third, smaller fence positioned several dozen yards behind the second fence. Rep. Duncan Hunter of California had originally conceived of a three-layer system for the border near San Diego, but construction was halted after the second fence was built.

The idea for multiple layers of fencing comes from a government-sponsored study published in 1993. Researchers from the Sandia National Laboratories determined that single barriers would not be nearly as effective as a multilayer system with permanent lighting and patrol roads. The report recommended the construction of three barriers—including a 15-foot iron-mesh fence in the middle and a 10-foot chain-link fence behind it.

Got a question about today's news? Ask the Explainer.

Explainer thanks Mike Friel and Todd Fraser of U.S. Customs and Border Protection and Joe Kaspar of the office of Congressman Duncan Hunter.

Print This ArticlePRINTDiscuss this in The FrayDISCUSSEmail to a FriendE-MAIL
Share on FacebookPost to MySpace!Share with MixxDigg ThisShare with RedditShare with del.icio.usShare with FurlShare with Ma.gnolia.comShare with SphereShare with Stumble Upon
Daniel Engber is an associate editor at Slate. He can be reached at .
Join the Fray: our reader discussion forum
What did you think of this article?
POST A MESSAGE | READ MESSAGES
Washington Post
The Washington Post
OPINIONS
Let the Oil Deals Flow
Raad Alkadiri | Congress should not interfere in the oil industry's contract negotiations with the Iraqi government.