Second reply... hoping i don't make a fool of myself...
There are valid reasons for both the Newtonian and the Einsteinian universes that shoot down the great "smoot to alpine" race.
Newtonian - Newtons second and third laws. Equal and opposite forces are exherted by each "child" truck upon it's parent as it's wheels push its parent backward in order to move forward. This force is proportionate to mass, but opposite in direction, and the total energy of the system must be conserved. f = ma for entire system. Hence the smallest stacked trucks' "speed" never exceeds the vector average of the system. ( not sure of the mathematical correctness of that last sentence, RC... Close?)
Einsteinian - We all hear the term "relativity". Einstein (well, acutally Lorentz) used this term to mean "one frame of reference in relationship to another", or their relative mass-energy states. The system of trucks in "the great Star Valley race" , are all one "frame", so even ignoring newtons equal/opposite force of child to parent... even if the children trucks could "magically" accellerate without force upon their parent , which they can't ... even if they could, none of the children would exceed the limits of the frame of reference. To put it in plain english, the children trucks would ALL BONK into the cab of their parent, imparting energy to it and destroying themselves in the doing. The total energy of the "system of trucks" AS SEEN FROM WITHIN the cab of the massive "monster mama" remains constant as it approaches the speed of light. You do, however eventually obtain a "single really, really massive truck, if observed FROM OUTSIDE the "frame", because the truck gains mass/energy as each child destroys itself in the "collision" with it's parent. (the mass to energy thingy, e = mc 2) Eventually all the children have destroyed themselves, imparting energy to the "big mama" truck rig, but the speed limit is safe.. Big mama gets fatter and fatter, but she cain't run no faster!
Relativity might be said to be the information differential as observed from inside big mama's cab as compared to an observer watching her pass from the grandstand down the final straightaway! She's doing 99.999997! Oh my God! She is flying!
From the grandstand... the sixty mile long truck would seem like a big flat plate as it whizzed by you. She would be a "paper thin", borg cube at full impulse! (Not to be confused with Barb'Q which is cooked in the parkin' lot before the race!)
As one approaches the speed of light, (or as i prefer to think of it... the "maximum information interchange rate"
if you were in the cab of the "monster mama" truck, your vision would shrink from all sides until you observed a large "cone" straight ahead of you. Ever nearer the speed of light, the cone shrinks to become a single overpoweringly bright, tiny dot. The reason is that all other information coming from the sides, and behind you... never arrives. An "information cone" to the front shrinks smaller and smaller until it becomes a single dot. The universe at near the speed of light is strikingly analogous to a black hole in this sense. It is truely a weird place in which we live. I apologize if this does not make sense. I have a "sort of" feel for relativity, but words fail, and i am sure i might be off on several important aspects. Without "math" ability, i am stuck in a world of guess and hope. That is why i envy RC and the rest of you who can actually do math. What a wonderful thing to not have to rely on verbs and adjectives! Mike