George Harris
Engineer
Blue Marble and JIS, I was for the most part offline and not visiting here even when I was in early to mid April. Seems like my presence was requested on a couple of issues:
Superelevation and unbalance, or in Eurospeak, Cant and cant deficiency"
The normal maximum superelevation in the US railroad world is 4 inches or less. However, up to 6 inches is normal in transit systems as they do not have to contend with high center of gravity cars. The normal maximum in much of the rest of the world is usually 150 to 160 mm, which sounds a lot like 6 to 6 1/2 inches.
The normal maximum unbalance is 3 inches, which also in the FRA limit (213.57) except it may be up to 4 inches case by case in (d) under the same 213.57, which describes the steps needed to get this approval. Height of center of gravity of the vehicle is part of the process, although not labeled as such. 213.57(d)(1) and (2) define maximum unloading of the wheel. In much of the world this unbalance may be up to 100 to 110 mm, in other words, 4 to 4 1/2 inches.
As has been said, both the 3 inch and the 4 inch values are well inside the limits of safety. However, once you get above 3 inches the lateral force becomes quite noticible.
However, since freight moving at under the balance speed for the curve severely beats up the low rail (inside rail) the normal railroad practice is to reduce superelevation to the point that it balances or is slightly below that which balances the normal freight train speed on the curve. Therefore, a curve which might be good for say 70 mph if it had 4 inches of superelevation might only be given 2 inches due to the average freight speed, resulting in a lower maximum speed. I am going to be lazy and not figure out an example.
There are a few reasons that the engines pulling the Talgos do not need to tilt: First, as noted, there is no safety issue. Second, the engineer is sitting down and looking down the track, so that lateral force is less of an issue, and he can also see what is coming.
The impact going in and out of a curve is not that big a deal. Railroad curves have spirals, that is, a curve with variable radius decreasing from infinity to the curve radius over a given length. I will skip the details of that for now, also. The sprial spreads the increase in lateral froce of a specific length of track.
more later - maybe
Superelevation and unbalance, or in Eurospeak, Cant and cant deficiency"
The normal maximum superelevation in the US railroad world is 4 inches or less. However, up to 6 inches is normal in transit systems as they do not have to contend with high center of gravity cars. The normal maximum in much of the rest of the world is usually 150 to 160 mm, which sounds a lot like 6 to 6 1/2 inches.
The normal maximum unbalance is 3 inches, which also in the FRA limit (213.57) except it may be up to 4 inches case by case in (d) under the same 213.57, which describes the steps needed to get this approval. Height of center of gravity of the vehicle is part of the process, although not labeled as such. 213.57(d)(1) and (2) define maximum unloading of the wheel. In much of the world this unbalance may be up to 100 to 110 mm, in other words, 4 to 4 1/2 inches.
As has been said, both the 3 inch and the 4 inch values are well inside the limits of safety. However, once you get above 3 inches the lateral force becomes quite noticible.
However, since freight moving at under the balance speed for the curve severely beats up the low rail (inside rail) the normal railroad practice is to reduce superelevation to the point that it balances or is slightly below that which balances the normal freight train speed on the curve. Therefore, a curve which might be good for say 70 mph if it had 4 inches of superelevation might only be given 2 inches due to the average freight speed, resulting in a lower maximum speed. I am going to be lazy and not figure out an example.
There are a few reasons that the engines pulling the Talgos do not need to tilt: First, as noted, there is no safety issue. Second, the engineer is sitting down and looking down the track, so that lateral force is less of an issue, and he can also see what is coming.
The impact going in and out of a curve is not that big a deal. Railroad curves have spirals, that is, a curve with variable radius decreasing from infinity to the curve radius over a given length. I will skip the details of that for now, also. The sprial spreads the increase in lateral froce of a specific length of track.
more later - maybe
