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.
In between shifts, the driver must generally be off duty for at least 10 consecutive hours. Moreover, a driver cannot accumulate more than 60 hours of on-duty time during 7 consecutive days or 70 hours during 8 consecutive days. It is important to keep in mind that this restriction applies to on-duty time, not driving time.