Earlier this week I was in Dallas, and I took the opportunity to visit one of my favorite train watching spots. It is the platform at Dallas Union Station, where one can see DART light rail trains, TRE trains, Amtrak’s Texas Eagle, Union Pacific freights, BNSF freights, and Dallas, Garland and Northeastern freights.
Whilst I was there a UP freight came bye. One of the cars has a flat spot on one of its wheels. If noise is an indicator of the severity of the flat spot, it was pretty large, which raises this question. At what point does a flat spot on a wheel represent a hazard, i.e. it could cause a derailment?
From NORAC (and I’m sure just about every rule book)
"71. Flat Spots
If a flat spot on a wheel of a car or engine develops en route, a member of the crew must inspect it. Upon completion of inspection, the train will be governed as follows:
a. Proceed at Normal Speed: The train may continue at Normal Speed if no other defects affecting movement are observed, AND if:
The flat spot is less than 2½ inches in length, OR
If there are 2 adjoining spots, each is less than 2 inches in length.
b. Proceed at 10 MPH: If a flat spot is found in excess of either of the above dimensions, but less than 4 inches, and no other defect is observed, two actions must be taken:
Speed must not exceed 10 MPH.
A report must be made promptly to the Dispatcher or Operator.
c. Remain Stopped: If a flat spot of 4 inches or greater is found, the train must remain stopped until a report is made
With the sheer number of flat spot detectors (impact detectors) major flat spots are not as common as they once were, but they still happen.
The car will be cut out at the first chance, if the wheel is condemnable.
First good roll by from an opposing train meet will also “find” the flat spot.
Unless the brake is locked and the flat spot is huge, the major concern is not derailing the car, but damage to the track, switches and frogs.
What will happen if the wheel is not replaced is that every time the brakes are applied, the flat spot will find the rail, the wheel and brake will lock and the wheel will slide on that spot, making it even worse and bigger.
Railroads and agencies provide a ruler or scale in or on timetables, schedules, and as a separate paper or ruler which can be used to measure the flat spot and tells what to do at each length. There are many results of flat spots. To the wheel itself, it can get bigger and/or cause the wheel itself to crack. To the track it has a hammer effect that can cause damage to the rail, frogs, etc. To the car it can give a jarring ride and cause other appliances to have problems of coming loose, etc. If you do hear something like that, you should report it to a railroad person citing the car’s identifying marks and as well as possible the location of the car in the train (some buffs are actually counting cars, so it is easy, others a good guess of halfway or 3/4th of the way into the train, near the end, or note cars before or after it).
Two things I know of right off that will cause a wheel to bang is flat spotting and shelling. With shelling the wheels surface is actually breaking apart and can result in catastrophic failure of the wheel. In every instance of shelling that I’ve seen the car was dropped at the first available siding or terminal.
My carrier has a Wheel Impact Detector on my territory. The detector will activate at 4 levels of impact. The 1st and 2nd levels are of relatively minor signifigance and a records of the impact is placed against the car’s running record while it is in the system. The 3rd level is more serious and Dispatchers are instructed to notify the train that they have this particular car(s) and to reduce speed to 30 MPH and continue to the nearest Terminal for the car to be set out. The 4th level is serious, Dispatchers must instruct the train to STOP and inspect the identified car(s) and see if they are safe to move. If they are safe the train will proceed at not exceeding 10 MPH to set the car off in the nearest set off location. In my carriers implementation, trains do not receive a Detector initiated message about the occurence, Dispatchers receive the initial notification from the CADS system and must notify the trains.
The detector is located at MP 117 on the subdivision and is used primarily to protect loaded coal trains, by the time the warning reaches the Dispatcher the train is normally in the vicinity of MP 105 and it will get stopped at MP 103, the nearest set off location is at MP 94. When it is necessary to set a car off, the minimum delay to the train is 3 hours. If the crew’s inspection reveals the wheel has built up tread from stuck brakes, the Car Dept must be dispatched and the crew will then be governed by the Carman’s instructions in moving the car to the set off location. When the Car Dept gets involved, the minimum delay grows to 6 hours.
In some cases, cars that initiated Level 3 identification when measured under load (30 MPH) have gone onto the destination terminal (and shop) and have not been repaired for a variety of reasons. The car has not activated the WID when making the empty move over it. The flat
BaltACD, thanks much for sharing that explanation, those insights, ‘rules of thumb’, and the anomalous non-detection of an empty car’s flat spot(s) after having previously detected it (them) while loaded . . . [:-^]
A few years back, Jeff Hergert here answered my similar question by stating that a condemnable wheel can usually be heard ‘thumping’ on the rail from around 5 to 6 car-lengths distance, so that provides a little bit of time to take some kind of preventative action.
Good information in all of the previous posts. I’d like to suggest, however, that you may not have heard a flat spot on a wheel. I have had many experienced railroaders say that they heard a flat spot that turned out to be a brake shoe that had only partly released. The major differences are that flat spot noise doesn’t change rhythm without the train speed changing and flat spot noise doesn’t suddenly stop while the train is still moving.