It depends on which area of the Code of Federal Regulations (CFR Title 49, Transportation) that is being discussed.  The exemption in Part 383.3 related to commercial driver's licenses is 150 miles. The exemptions in Part 395.1 related to log books is 100 air miles.  The intrastate exemptions for farm operations in North Dakota (CDL requirements, medical certificates, log books, and vehicle inspection records) are 150 air miles (reference NDCC 39-06.2-17).