绝对闭塞

建

Block system \Block system\ (Railroads)
A system by which the track is divided into short sections,
as of three or four miles, and trains are so run by the
guidance of electric, or combined electric and pneumatic,
signals that no train enters a section or block until the
preceding train has left it, as in

{absolute blocking}, or that a train may be allowed to follow
another into a block as long as it proceeds with excessive
caution, as in

{permissive blocking}.
[Webster 1913 Suppl.]