It's an old joke, inspired by everyone's nightmares of high school algebra: A train leaves New York going West at 100 miles per hour. Another train leaves LA going East at 200 miles per hour. How much of a mess does it make when they collide, and who has to clean it up?

There is another coming collision, though, and this one is significantly less funny. As a recent NY Times article described, the US is seeking to codify the rights of forces operating in Iraq through a Status of Forces Agreement (SOFA), which would take effect after the UN mandate expires at the end of this year. Normally, this would be a welcome step in the right direction, as it further cements Iraq's status as a sovereign nation rather than an occupied power. Nor is there anything abnormal about a SOFA -- similar agreements have governed the actions of US forces and civilians in Germany, Italy, and Japan for decades. What is worrisome, however, is one particular provision the US is apparently stipulating:

The Bush administration will insist that the government in Baghdad give the United States broad authority to conduct combat operations and guarantee civilian contractors specific legal protections from Iraqi law, according to administration and military officials ... the American quest for protections for civilian contractors is expected to be particularly vexing, because in no other country are contractors working with the American military granted protection from local laws.

For one thing, this shows a complete tone-deafness to one of the sorest points in local Iraqi politics. Rightly or wrongly, American contractors, especially security personnel, are perceived as lawless, vicious, and out of control by many in the Maliki government. Not allowing the Iraqi government any control over misconduct in this area will undermine attempts by elected officials to be seen as true representatives in their own right rather than puppets.

But what will truly cause the coming collision is not the Iraqis' perceptions, but our own failings. As administration officials noted in recent hearings, the US is simply unable to exercise oversight to any significant degree over the operations of contractors in our theaters of war. The numbers are stunning. The contracting oversight workforce in DoD has shrunk by 10% since the 1990s, while our reliance on contractors has increased sevenfold. $10 billion in contracted money paid out cannot be accounted for or paired with any kind of meaningful results. 80 separate investigations are underway involving contracts of greater than $5 billion.

So on one hand, we will deny the Iraqis the ability to prosecute contractors for misconduct, a right we grant to every other allied power with whom we have a SOFA. On the other hand, we are completely unable to proactively manage or control our own contractors, and are only fitfully managing to play catch-up on the messes made so far. All of the ingredients will soon be in place for a colossal disaster.

Private security companies such as Blackwater and Triple Canopy might appear to be the biggest dangers here, but I suspect that the spark that sets this particular powder keg off will be far more mundane. Rather than the spectacular fireworks of the September 16th shootings, I believe the triggering incident will be far simpler -- most likely a vehicle accident, perhaps a crash of a semi-trailer into a popular civilian gathering place, such as a market or a mosque. To get a sense of what it could look like, witness the furor triggered by the accidental crushing of two Korean girls by a US convoy in 2002. Now throw that into simmering sectarian tensions in Iraq, and it's depressingly easy to see how a minor incident with no accountability of the perpetrators could easy snowball into something bigger.

The trains are on the rails and underway. The only question is, can we avert the coming collision in time?