Every expenditure of money entails a consumer surplus component. Before we could conclude that there would be net benefits by extracting funds from taxpayers and diverting them to subsidizing transit, we would need to know the full cost of the foregone uses of this money, we would need to estimate the consumer surpluses that would be sacrificed in the myriad of purchases made infeasible by the taxes taken for transit subsidies. The fact that making such an estimate would be difficult and prone to error is not a rationale for dismissing it. Reduced Congestion Measuring congestion costs is just as difficult as measuring mobility benefits. While it may be relatively easy to put a value on the fuel consumed, fuel is a small component of the cost.
Time is the largest component of the cost.
Estimating the value of time lost in traffic congestion is subject to large ranges of error. Different drivers place different values on their time spent in traffic. This means that more than half the drivers are choosing to join the traffic jam. Apparently, these individuals place a very low value on time lost in this way. Another illustration of the problems associated with valuing this lost time is the fact that only a minority of vehicles in the California SR 91 corridor choose to save time by paying to use the HOV lane.