What kind of bridge would this be?

If it's a plate girder style, then it's fairly easy to put a couple of unobstrusive door hinges on the floor of the bridge so that it can be lowered when not in use.

If it's a truss bridge, it can be done the same ay by attaching a plate of some sort under the floor of the bridge for attachment of hinges so that it, too, can be lowered when not is use.

If you want to be able to raise -- rather then lower -- the bridge, then the situation becomes a little more complex because the pivot point of the hinge has to be above the railhead.

I hadn't considered lowering the bridge!  I guess I just need to allow for the opening to accommodate the bridge length and width.  I'm trying to avoid crawling under the table!!!

I've always been attracted to lift bridges (above the table) with some mechanical assist to keep it above the table. 

Any suggestions are appreciated. 

I used a lift bridge for the entrance to my yard.  I considered a drop bridge, but the issue of exact alignment of the tracks is complicated by the drop direction.  For the lift bridge, it just comes down and aligns on two large brass alignment pins, perfect alignment every time.  I had ten tracks to contend with, so alignment was a major consideration.

The black plastic was to adjust the height of the bridge to exactly match the yard surface.

GRJ,

Your picture really helps a lot.  It would appear to be a door hinge (3) with the hinge pin at the level of the top of the track.  What do you use to keep the rather large and heavy bridge from falling?

Thank you for sharing

@gunrunnerjohn posted:

I used a lift bridge for the entrance to my yard.  I considered a drop bridge, but the issue of exact alignment of the tracks is complicated by the drop direction.  For the lift bridge, it just comes down and aligns on two large brass alignment pins, perfect alignment every time.  I had ten tracks to contend with, so alignment was a major consideration.

The black plastic was to adjust the height of the bridge to exactly match the yard surface.

Where did you buy the "two large brass alignment pins" ?

@Windy City posted:

Where did you buy the "two large brass alignment pins" ?

Actually, a friend of mine that was a huge help in the fancy carpentry of my layout had them.

You just drill a hole through the two mating surfaces of the correct size with the closure aligned properly and then screw the two mating parts into the two holes.  After that, the brass pins align the mating bridge perfectly when closed.

Freeman Square-Head Brass Dowels