At the military base I work on dozens of people take a private car from the base to the airport per week for official travel. There is nothing wrong with this, its allowed in the Joint Travel Regulations, but there's significant opportunity for savings here. I think every military base & every other government facility that sends more than about 10 travellers per week to the same airport could save thousands of dollars by establishing a shuttle service to the airport. Even if it only ran on the two busiest travel days per week, I'm sure it would save significant dollars.
Idea No. 16332