41 CFR 302-10.100: -10.100 Allowable distance for points of origin and destination within CONUS and Alaska.

Agencies will allow for the distance shown in standard highway mileage guides or agency designated official table of distances or actual miles driven as determined from odometer readings, between the authorized origin and destination. Employees do not need to furnish odometer readings on the travel claim but must indicate the total miles traveled. Any deviation from the distances indicated in standard highway mileage guides or agency official table of distances must be fully explained and acceptable to the agency.