How much can the rail curve?

Question

This would be at slow speed approaching a station.

Answer 1

90 degree

Answer 2

You can tighten the curve as much as you wish, to the point where it'll go no more.

The question is, what will be running on it?  The lighter and shorter the equipment is the tighter turn it can negotiate.

An excellent example is some industry tracks.  Very tight turns usually restrict the locomotive used to no more than four axles.  The six axle unit's trucks are too long to negotiate the curvature, and the overall length of the locomotive is greater.

So, without any parameters, it's kind of hard to say for sure.  

I have lots of operators' manuals.  Give me a few minutes and I'll give you what the locomotives are rated for.  It may not be until tomorrow.

OK.  Here ya go:

For an EMD SW1500:

1.  Truck swing limits single unit curvature negotiation to a 60 degree or 100 ft. radius curve.

2.  Two units coupled are limited by footboard clearance to a 38 degree or 154'  ft. radius curve.

3.  Locomotive coupled to a 50 foot car is limited by coupler swing to a 40 degree or 146 ft. radius curve.

For an EMD GP9:

1.  Minimum curve radius coupled to a car, 150' (39 degrees)

2.  Coupled to another locomotive of same type with type "E" coupling, 274' (21 degrees).

For an EMD GP20:

1.  150 ft.

For an EMD F40PH Passenger Locomotive:

1.  Truck swing limits single unit curve negotiation to a 43 degree 10' or 135 ft, radius.

2.  Two similar units coupled in multiple limited by coupler swing to a 33 degree or 175 ft. radius curve equipped with "F" type couplers.

3.  Locomotive coupled to an 89 foot passenger car limited by car coupler swing to a 18 degree or 315 ft. radius curve equipped with "F" type couplers.

4.  Locomotive coupled to a standard 50 ft. box car limited by car coupler swing to a 23 degree or 250 ft. radius curve.

If ya need more, I've got ops manuals for EMD, Kraus Maffei, Morrison Knudson, GE, Alco, Fairbanks-Morse and Baldwin units.

So, given the common locos above, you've got a good idea now.  Sorry I can't give you any stats on light rail, but I would imagine it would be safe to say they can turn tighter, but I really don't know.