Answer: sunk costs don't increase as driving increases.
Explanation: sunk costs are irrelevant costs because they have already occured in the past and cannot be avoided. Sunk costs thus do not differ between alternatives, and are unavoidable. The calculation for insurance and other sunk costs are likely not based on the amount of rides the Uber picks up, but rather calculated at a constant rate. So regardless of whether or not the rider pays more or less than the $.50 on the insurance, this will not have any effect on the insurance that is constant and has likely already been paid out.