THE most economically important connection between the United States and Canada is Detroit's Ambassador Bridge. Nearly a quarter of all trade between the two countries - $150 billion a year - moves across it, the vast majority of it material for the auto industry. Without that vital artery, the economies of Michigan and Ontario would be devastated and Ohio's would be severely damaged.
Yet amazingly, the bridge is perhaps the weakest link in our security-mad world. The bridge is owned not by the governments of the two nations, or by Michigan and Ontario, but by one reclusive, very rich 80-year-old man, Manuel "Matty" Moroun.
The problem isn't that he shuns the media; it's just that he claims he doesn't have to answer to anyone for what he does with his bridge. He has refused to allow either government to inspect it, and he claims neither the laws of Canada or the United States apply.
Forbes Magazine calls the Ambassador "an undefended economic umbilical cord" and our nation's "most critical choke point" when the discussion turns to terrorism and trade. If something were to happen to it, there is no backup system; most of the 9,000 cargo-hauling trucks that roll across it couldn't fit through the Detroit-Windsor tunnel, which is designed for cars.
Yet not only is the Ambassador unguarded, gasoline tankers are allowed to park under it. Though nobody except Mr. Moroun knows the true condition of the bridge, it is clearly time for a new one.
It was built in 1929, and its lanes are too narrow and the approaches too steep for today's trucks. After opposing one for years, Mr. Moroun now says he intends to build a new bridge - right next to his old bridge.
A group called the Detroit River International Crossing, or DRIC, thinks there is a better way to go.
They want to build a new, secure, publicly owned bridge about a mile south of the present one, where an area of Detroit called Delray faces the Windsor suburb of Sandwich.
Their plan is supported by all the governments involved, and by the automotive industry, which made it clear it has security concerns with Mr. Moroun's bridge. Yet now Michigan's cash-strapped government has been hinting it might pull out of DRIC, because a publicly owned bridge would be more expensive. That would be a mistake, one that could have devastating consequences.
There is nothing wrong with private ownership as long as it doesn't threaten the public safety. Nobody is suggesting that Mr. Moroun should have to abandon his bridge. But a backup would be a smart idea.
We live in a world where the airlines confiscate bottles of shampoo for security reasons. There can be no excuse for not making sure our most vital economic lifeline is truly secure.