Truck drivers are limited to the amount of hours they drive per day by law to prevent them falling asleep and getting fatigued and to prevent causing a crash.
The average truck driver is expected to drive between 2,000 to 3,000 miles per week and with around 4 weeks per month and 12 months in a year that would come to 96,000 miles to 144,000 miles per year.
That's quite a bit more driving than the average person puts on their personal vehicles pear year as an average personal vehicle gets around 10,000 to 12,000 miles per year put on the vehicle but a semi truck driving cross country gets more miles put on.
The average semi truck is expected to last at least 1 million miles and sometimes more and even then the engine and transmission is sometimes replaced instead of replacing the entire truck because a new semi truck costs a lot more money than a regular truck.