On a family-type Suburban:
Awwww. On a nice SUV:
Only in this city, I'm telling you.
And the best of the lot this time around, on a white convertible Mustang:
Either the guy has a huge ego, or a girlfriend (or boyfriend) with a strange sense of humor. Heh.
The Unquantifiable Variable, by BeckyS (this archived at the CalSci Library).
This is a nice, longish, character-accurate fic. The idea is one that is used a lot in fanfic (character A is a hostage in a robbery gone bad; character B is part of the team working to save them), but this fic is well-written, the character voices are solid, and there is no question that this is a Numb3rs story--can't just change the names and a few details and have a story for another fandom. For one thing, there is actual math involved. :-)
One more note: it's clearly set, say, late first season.
Alan accepted his answer, but he wasn't finished. "If it's not your past with your brother that's tearing you apart, then what is it?"
[Don] paced to the front of the car and gazed over the parking lot. The tools of his trade -- the men and women, the vans, the threads of communications that connected them all, that held the operation together -- everything was laid out in front of him. He turned back to his father. "The future," he finally blurted. "Dad, I have to do my job. I have to be objective, I can't afford to remember that my brother is inside, because if I do, I'll miss something and he could die. And I have to consider all the angles, consider the welfare of all the hostages -- not just Charlie -- and all the citizens I'm sworn to protect, and that means I also have to consider sacrificing him in order to get this guy."