Mileage Statistics gives a compact and comprehensive list of how far you have travelled within each individual journey, this allows for you to accurately monitor your vehicles use in case of breakdown or just making sure that your workers are making the most efficient journey possible.
Menu (Top Left) > Report > Mileage Statistics
You can find how to access and use Mileage Statistics here: https://www.youtube.com/watch?v=p-2KDjToagk