Question about curve radius/weight

Cantara Loop guard rail.

 

 Real railroads need to worry about coupler compatible on sharp curves in switching and street trackage.  I know of no place where mainline curves are an equipment compatible issue.  On real trains the wheels are pressed tight on the axles.  So when a train goes around a curve, one of the wheels has to slip.  On a long train on sharp curves it can take a lot of horsepower to overcome curve resistance.  It also presents train handling problems, especially if there is also grades involved.  Some parts of the train may be pulling while others are pushing, all at the same time.  I had an opportunity to measure the speeds of different cars in the same train at the same time on a curvy mountain railroad.  We found different parts of the train with speed differences of much as three mph. When these parts of the train running at different speeds finally catch each other, there can be harsh jerks that can break a train apart or even derail it.

 

As far as rail size goes, at one time there was light rail that would support large locomotives.  70 pound rail will not support a GP.  That is not to say it will break, but over time the rail will become bent and it will no longer be possible to line or level the track, so it will just continue to deteriorate.  This problem is made much worse with bad ties and wide tie spacing.  Today the problem is not so much of the rail to support the load, but the fatigue life of the rail.  On a busy high tonnage trail road the rail is changed not based on wear, but on how many tons have gone over it.  On the heavier cars today the surface of the rail may actually flow due to the extreme load placed on it.  Different rail sections hold up to these extreme forces better than others.  Different railroads have different ideas about which sections are best, but I think there is finally agreement on ideal rail sections developing.     

Not just BIG railroads, either. When the Strasburg Rail Road built a freight loading/unloading facility on the far end of the parking lot, opposite the enginehouse, the curve and runaround track at Lehman Place Junction had to be widened to accommodate longer, heavier modern freight cars. The Strasburg's one and only bridge had to be replaced, too. Wood was replaced with concrete. This new bridge won an award for design. RAILFAN & RAILROAD Magazine ran a news story about it.

 

This project is evident in videos of Great Western 2-10-0 No. 90 on YouTube.

 

The stub of the original runaround track is still there, but locomotives now run past it on a curve outside the main.

Small old rail that was subjected to heavy loads, after being unspiked for salvage.

 

Thanks for the detailed info. It is appreciated.

For what it's worth, you might like to correct your "screen name", since the correct EMD model name is DDA40X, and NOT "dd40ax" sic.

At Union Pacific we just called them DD40 for short. Not like we were going to confuse them with anything else.

 

The operator manuals published by the builder ,as well as the railroad mechanical engineering standards, listed the maximum allowable curve (in degrees) for each class of locomotive.