This is a tunnel mouth or bridge arch made from 27 track links.
The track links are fixed each side in 2 places, at the top of
the straight sides and at the bottom, using 3M axles with stud.

The natural arch width with 17 links free to curve is 17L.
This arch is 16L wide to make an even number of modules width.
This should be sufficient for all but the greatest overhangs
from 6 or 8-wide trains.  I might make the arch a bit wider
for my 8mm scale trains, to allow a loading gauge of 5M
either side of the track pieces.

Since the track links are dark bley, it makes sense to use
other bley and dark bley parts with them.  Blending them in
with natural scenery is for further experiments.

Smaller arches with less than 180 degrees of curve can be
constructed.  The links fit with plates 1x1 and 1x2 modified
with clips and bars, which are likely to be the best means
of attachment for non-vertical links.

Mark Bellis
February 2007