but #158s are even more critical. My plan is to use Sergents
on my home switching layout, but I would not consider them
or the #158 for use on the modular club layout setups. The
dips and bumps that seem to be standard with modular lay-
outs that are set up and taken down repeatedly seem to
invite nuisance-uncoupling without adding to the problem
with small coupler heads.”
Mixing Kadees:
Signals
Q.
What’s the difference between an absolute block system
and a permissive block system? I’ve been trying to read up on
signals, but can’t find the answer.
A.
An absolute block system allows only one train in a block at
a time. A permissive block system allows more than one train in
a block at a time. Using rules and signals, a permissive system
allows one train to follow another in the same block.
Just to throw in another confusing term, a common system in
use in the U.S. today is absolute permissive block, which pro-
vides full signal protection for opposing trains in addition to the
protection for following trains that an automatic block system
gives. (Most single track ABS systems provide some protection
against opposing trains but the protection is not complete, and a
track occupation authority system like timetable & train order or
track warrant control is needed.)
Here’s good web page that tells the basics of railroad signals:
Jay S. Bogguss wrote a series of five articles that started in
the November 1991
Model Railroader
that will tell you about
everything you need to know about absolute permissive block
Questions, Answers & Tips -
MRH-May 2014
