> If your referring to the changes of about 10 years
> ago which require that dynamics must be functional
> upon leaving the initial mechanical facility,
> these were brought about because the RRs were (and
> still are) coercing their engineers to use
> dynamics as the prime braking system on the train.


True - There were changes to the mechanical rules requiring the maintenance of dynamic brakes and notifying crews of their condition, but I was referring to the change in operating rules, typically found in the Special Instructions.

Part of the reason railroads coerce their crews into using dynamics as their primary braking is to discourage stretch braking with its higher fuel consumption. Personally I use whatever method is available that provides the best train handling, but its been years since I ran a train with working dynamics and track good enough to use it on.

As dynamics and pressure maintaining took the place of cycle braking and retainers, railroads increased the tons per operative brake. There was also a shift to unit trains of all loaded cars, in addition to an increase in car size, substantially raising the tons per operative brake on many trains, high capacity dynamic brakes with extended range - not to mention the huge increase in train length and size, or use of Locotrol/DPU.

As was already mentioned, railroads have pushed the limits of how large a train can be safely controlled requiring the combined use of both dynamics and train air brakes often at their maximum limits. As dynamic brakes are not fail safe, and the engineer only has limited indications of them functioning properly, an unexpected partial or full failure results in the acceleration of the train. Assuming the engineer recognizes this in a timely manner, their first reaction is usually to try to regain control of the train. An immediate emergency brake application is generally avoided except as a last resort, as this carries risks of its own and once an emergency brake application occurs for any reason, the engineer actually has few options but to ride it out. Too many engineers either fail to recognize they are losing control of their train (either by lack of attention, training and/or available information) until the train speed gets too far out of hand. Assuming that the engineer's eventual emergency brake application carries through the entire train, they often find themselves in the situation where train speed has increased beyond the point of no return and the brake application is ineffective, or soon becomes so due to the failure of the brake shoes due to excessive heat, or the train simply can't stop or slow enough before it runs into a restrictive curve, another train, etc.

This is the specific FRA regulation change I was referring to, the mechanical requirements are just before it.


49 CFR § 232.109 Dynamic brake requirements.

(j) A railroad operating a train with a brake system that includes dynamic brakes shall adopt and comply with written operating rules governing safe train handling procedures using these dynamic brakes under all operating conditions, which shall be tailored to the specific equipment and territory of the railroad. The railroad’s operating rules shall:
(1) Ensure that the friction brakes are sufficient by themselves, without the aid of dynamic brakes, to stop the train safely under all operating conditions.
(2) Include a ‘‘miles-per-hour-overspeed-stop’’ rule. At a minimum, this rule shall require that any train when descending a section of track with an average grade of one percent or greater over a distance of three continuous miles shall be immediately brought to a stop, by an emergency brake application if necessary, when the train’s speed exceeds the maximum authorized speed for that train by more than 5 miles per hour. A railroad shall reduce
the 5-miles-per-hour-overspeed-stop restriction if validated research indicates the need for such a reduction. A railroad may increase the 5-miles-perhour-overspeed restriction only with approval of FRA and based upon verifiable data and research.
(k) A railroad operating a train with a brake system that includes dynamic brakes shall adopt and comply with specific knowledge, skill, and ability criteria to ensure that its locomotive engineers are fully trained in the operating rules prescribed by paragraph (j)
of this section. The railroad shall incorporate such criteria into its locomotive engineer certification program pursuant to part 240 of this chapter.
[66 FR 4193, Jan. 17, 2001, as amended at 67 FR 17581, Apr. 10, 2002]


As I recall, these changes were in part prompted by another Cajon Pass runaway, the SP soda ash train with under reported tonnage and engines with out of service dynamics. No does the FRA actually audit compliance with this - I have no idea.