[jaksawesome]

They're not efficient ways to deliver to consumers, but to delivery units like the local post office they're remarkably efficient (especially for rural areas). The biggest cost savings to be had would be to deliver from a local warehouse to the nearby DU, where you would pay the last mile carrier to do the heavy lifting. The issue you run into is that there's no appetite for increasing the load at these units, so no appetite for innovation until the infrastructure improves.