Most proposals to replace the fuel tax with an MBUF only focus on the fuel tax’s declining revenues, since a large fraction of vehicles will be using less or no fuel in the coming decades. But this hundred-year-old tax has other shortcomings. If Michigan and other states are going to replace it with a better funding source, the MBUF should be designed to fix the shortcomings of the fuel tax. Here is a brief explanation of those shortcomings.