I built this 7.5 foot (2.3m) bridge in a matter of a few days just for our TexLUG train layout in March 2004. I sized it to fit exactly on 9 regular baseplates (32 x 32 studs each).

The pattern of the arch is really simple- each of the 11 segments are pinned together, and the geometry of the holes (i.e. hole spacing) is identical. 6 of the sections are 2 studs wider than the other 5 sections. This enables them to be pinned together (e.g. the smaller ones slot into the larger ones).

The deck is composed of parallel sets of LEGO train track. There are support hangers at each joint (e.g. every 16 studs), and the tracks are also linked together with plates.

This "deck" is placed under tension by the arch, as it wants to spread outwards. Think of it like a giant bow (as in bow-n-arrow), the bow wants to spread out, and the string keeps it bent by tension. But keep in mind that the LEGO arch isn't bent against itself, but rather gravity pulls the arch downwards, and therefore the ends want to spread out. Because it is very flexible, it will spread out quite a bit (until the track is in place). Make sense? I didn't think so :-)

I suspended the deck by simply "eye-balling" it. Each section of string was adjusted until the deck appeared somewhat level, and the tension was only slight.

We ran long trains over it at the TexLUG meeting, and the bridge performed quite well!

Specs:
• 288 studs total length
• 268 studs total span (unsupported length)
• 32 studs total width
• arch made of 11 pinned segments, pinned holes geometrically identical per section
• Double train track suspended from arch
• Track spaced with 8-studs clearance between them
• Arch wants to spread outwards, but track is placed under tension thus fixing the arch
• Bridge is strong and stiff- it can be easily picked up with two hands and moved

Typical Section Details: