down to HO. A car's overhang increases as the radius of a curve
decreases, and howmany model railroads have 60” curves? Not
too many. With truck centers set at 70', the maximumwidth the
AAR allows is up to about 9' 2”. Most freight cars are around 9' 6”
to 10' wide, so the safety margin is shaved to nothing or
exceeded on our layouts.
What's the solution? For one thing, the NMRA standards
gauge has changed over the years. A Mark IV gauge is a
couple scale inches taller and wider than a Mark II. Look
at
. The association
provides more suggestions about track center spacing and
clearances on curves at
Many modelers use a big double-door auto parts car or a
covered auto rack to field-test their clearances during con-
struction. If one of those monsters fits past platforms and
through tunnel portals, then other cars can usually make
it through. Steam-era modelers learned long ago that the
swinging boiler on a model Norfolk & Western Y6 or a Union
Pacific Big Boy can wipe out opposing traffic on curves that
are set too closely together.
Here's one way to keep your rolling stock and scenery safe.
On a flat surface, tack down a curve of flex track at your
planned minimum radius. Grab your longest and tallest cars,
and mark the amount of overhang at the cars' midpoints
and endpoints. Check the maximum height of the rolling
stock as well. Create your clearance guage out of styrene or
card stock with a slight allowance beyond those measure-
ments should give you smash-free operation.
Figure continues on next page ...
4: AAR plate H clearances for interchange, from the Official
Railway Equipment Register.
4
AAR rail clearances - 3
MRH-Jun 2013
