49 C.F.R. § 236.709 Block, absolute.
Title 49 - Transportation
A block in which no train is permitted to enter while it is occupied by another train.
Title 49: Transportation
PART 236—RULES, STANDARDS, AND INSTRUCTIONS GOVERNING THE INSTALLATION, INSPECTION, MAINTENANCE, AND REPAIR OF SIGNAL AND TRAIN CONTROL SYSTEMS, DEVICES, AND APPLIANCES
Subpart G—Definitions
§ 236.709 Block, absolute.