Mailing from coast-to-coast sounds like it would take a long time, but there are regular flights cross-country, and the sorting facilities bring mail to the middle of the coast, and then ship it straight across, east or west, depending. This means that the mail has to go first to a central sorting facility.
Truck and bus drivers must generally take a minimum of eight hours off between shifts, and their shift hours are often capped. Airline pilots are required to have 10 hours off between shifts to allow for transportation and rest time.
(Usually, however, Drivers will have had a 45 driving break before reaching the 6 hour point so this will not apply). A break of 30 minutes is required for 6-9 hours work; 45 minutes for over 9 hours. Breaks can be divided into 15 minute slots. First break must be at least 30 minutes.