Well, I don't know what world you live in, but I know that in my world, diesel exhaust is loaded with known human carcinogens...never mind lab rats. Indeed, there are around 200 known toxic compounds in diesel exhaust (although not all are carcinogenic). The state and feds are working to clean up the urban air by removing most of the sulfur (which is what the bad stuff gloms onto, forming soot, which we then breathe) from the fuel before it is burned. This is an elegant solution, and one that they've had in Europe for some time. Of course it takes us forever to get something like this in place, because it costs the refiners money to do it. And of course they will pass those costs along to us. But once all on-road users of diesel are using clean diesel, then the off-road users will have to start cleaning up as well (they've been given yet more time, until 2112 or so, IIRC). Estimates are that the wide-spread use of clean diesel will cut our urban air toxics risk by as much as 95%. That's huge. And when figuring the cost/benefit of slightly more expensive "clean" diesel, please remember to take into account the enormous health costs we're presently incurring due to "dirty" diesel.

Having said all that, I do find it ironic that you have to read a Prop 65 warning on the door on the way into Safeway. That's overkill, IMO.