Arnold Loop reminds me of the old horseshoe curve on the now abandoned Milwaukee Road line over Pipestone Pass, Montana. It was on the east side of Pipestone Pass between Vendome and Cedric sidings. The grade was 2%. It was broader in scale than Arnold Loop but the same idea. Like Arnold Loop access was very difficult by car to the actual curve. One of the coolest things was you could see westbound trains for a long time before they actually ever reached the curve. In the late 1970's all the slow orders plus the steep grade made for a lengthy wait to photograph a westbound train as you watched the headlight slowly creep up the hill out of Piedmont. By the time the train was in good photography range you had to hope the clouds didn't block the sun and screw up metering. The late ex-SP/UP locomotive engineer and railfan Doug Harrop had some excellent photos from Pipestone Pass over the years.