Correct, and this is something people often fail to understand about the free market. The market is making optimizations like the one you just suggested above (

Correct, and this is something people often fail to understand about the free market. The market is making optimizations like the one you just suggested above (using smaller trucks over larger ones) constantly, innovating to reduce costs in thousands of ingenious little ways no single person could possibly come up with on their own. And those optimizations aren't just confined to first order effects, they cascade across the entire market. A small change to the cost of transportation by truck will, over time, result in the entire economy making millions of small adjustments to optimize for that cost. But the market can't optimize for a cost it doesn't know about. If you're just funding road construction and maintenance with income taxes and people aren't paying those costs in proportion to usage, then there's zero reason for the market to do anything to try to reduce those costs.