How many "X-Rays" did I receive today?

Paraphrased from two posts to the CHEMED-L discussion list, yesterday and today.

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Today I was driving from Joplin, Missouri to Tulsa, Oklahoma along Interstate-44. On the way, I passed (overtook) four trucks which I recognized from news stories in the local paper as being the ones carrying low-level radioactive waste from the former uranium refinery at Fernald, Ohio to a Texas storage site. (see story and photo captions at http://www.joplinglobe.com/archives/story.php?story_id=101798 http://www.joplinglobe.com/archives/story.php?story_id=101443; the original news story seems to be unavailable online) Update: I found it at http://www.joplinglobe.com/story.php?story_id=191496&c=87. If you don't want to visit the links, here is a short quote:

Each of the flatbed trucks will carry two steel canisters, each weighing 21,950 pounds.

The canisters contain uranium residues, fly ash and portland cement. When combined, they form a solid concrete monolith. About 70 to 83 percent of the material in each container is non-radioactive, according to the U.S. Department of Energy. The department is overseeing the shipments.

Still, the waste is of some concern because it is radioactive. Standing close to one of the containers during shipment might be equivalent to getting a medical X-ray, according to the Nuclear Information and Resource Service in Washington, D.C.

Keith Stammer, the new emergency coordinator of Joplin-Jasper County Emergency Management, said the public should use what he calls the "thumb rule" with regard to the shipments.

"If you stick your arm out and hold up your thumb and if your thumb does not cover (the view of it), you are too close - just back up."

I also found the website www.fernald.gov and at that site, a fact sheet http://www.fernald.gov/NewsUpdate/PDFs/4-28-05%20Silos%201%20and%202%20Transportation%20Fact%20Sheet.pdf
According to the fact sheet:

Typical maximum radionuclide concentrations per waste package (pCi/g):
Radium 226 - 100,000
Thorium 230 - 15,000
Lead 210 - 100,000
Polonium 210 - 100,000
Actinium 227 - 2,000

So, let's assume that I passed within 2 meters of each of the 4 trucks/8 canisters at a rate (difference) of about 100 m/min (I did hit the accelerator a little). By stepping outside and holding up my thumb while looking at the entry door of an adjacent building, (without using any trigonometry or exact measurements) I'm estimating that the "thumb rule" is about 100 m, so I was inside that distance for a total of 8 minutes. Of course I was inside my car, so there was a little shielding. (And actually, the second through fourth trucks were close together, perhaps within the 100 m boundary, but let's ignore that).

Is there a simple way to estimate the dosage of radiation I likely absorbed? How would that amount compare to that from a typical medical X-ray (radiograph)?

An exact answer is not even possible, given the ranges from the fact sheet; there are just too many variables of which I have little understanding about for me to even make an educated guess. But it seems to me that before these trucks were allowed onto the public highways, that data would be available, presumably to the public. Suppose the federal government does have this data. What would it take to find it? John Stossel?

And yes, I'm worried about the drivers. I'm assuming that there is shielding built into the trucks and that any individual driver is limited to a certain number of trips and/or wears a radiation badge. But how would I know?

(Here are the best photos I could find; neither quite matches what I saw, but they're close.)