O27 Standard grade (slope) in degrees, for bridge approaches?

If you stick to short light cars like the postwar over/under figure 8 ,...maybe.

Im not sure on 60"... but 1 postwar graduated tressle.set.  About 4.5% grade.

It demands constant attention to the throttle or block control of.speed.

More realistic running your looking at 2.5% max. and that takes length.

I have a 4.5% grade to about 7.5" over about 18ft straight.

The postwar climb uses the curves for added traction.  (I cheat by using clear two sidded tape on one of the out rails, detacked a little. It acts like a traction tire. Lasts about a year or so. Peel off or lay some over that. Tires are a bigger pita, lol.

Next is how high? Height can vary from about 5¾-7½", maybe even 8" for a few cars like rocket launchers once launched and at a 45°, crane someone cranked the boom on, etc.  Do you like raised pantographs?..... 7"+

(I tie-wire my pant.s half extended )

Oh, wait, don't forget track types vary, so does the rail head height off the ground for them!  Gonna have roadbed?  etc.etc.

If you just want a small rise for the rear or something 6% to get 3" might be ok.   You need to think about locos under transition in and off grades too, angles can cause coupling issues, cowcatchers bottoming on the center rail(shorts cast Bodys too) and playing Dukes of Hazard comming down or teeter tottering up there.   There has to be gradual transition of soft grade into hard grade then more soft grade.

I don't know from degrees, but Warrenville does have a lot of elevated O27 gauge track.

Generally I at least double up the use of Lionel trestle sections at adjacent joints (ie: 2 D sections, then 2 C sections then 2 B sections, etc) to ease the grade.

All of Warrenville's curves are wide radius (O42, O54 or O72). If using O27 radius curves on grades I would use same trestle section heights on the approach to, and on the curve (ie: all B sections, all C sections, etc).

Adriatic said:   "If you just want a small rise for the rear or something 6% to get 3" might be ok."

Yes, that is all I am trying to do.  I will have five or six foot straight run on the rear edge of the the train table, and I just wanted to do a little something so that it isn't boring and flat.    Thee inches would be fine, because there will be no train tunnels running under it.

But with one side of the six foot run being the approach, and the other side the decent, it doesn't sound   like I could even get the track up 2 inches high.   Wow. That is disappointing.  

I guess I could start the upward grade in the long 34 inch radius curve that precedes the six foot straight away, but then things get more complicated.   Building curved ramps on each side of the layout was not really what I wanted to do.

Thanks for the excellent info.

Mannyrock

I'd suggest playing with the idea, literally.  Test your tolorence for running on it.   It's easy to get caught up in "wanting" ideas that may not be what you "need".  Running and experiments should reveal what truely entertains or satisfys you, try to leave the brain out of it until you find your style.

Grades are a fun challenge to pull  cars up. And with some careful planning you can do some hands free looping too.

Without planning you're stuck with working the throttles near as attentively as if you were running two locos on a flat fig.8 trying not to crash them.

Small grades can have big impact on throttle too. I try to get a video of a slight grade and apex on my shelf el section.  It usally creeps to the apex on a very low throttle, then practically runs down hill. There is also a power drop at the apex needed to climb, but a pita as it also causes the acceleration.  

Well Dang!

Thinking about a McGiver solution.

Cut a small section out of the train table top, that looks like a "ravine" ,  hang wire mesh down into in the ravine,  plaster the wire mesh sides at angles plunging down into the ravine, glue limestone rocks on the sides of the ravine all of the way to the bottom, span the ravine with the bridge, and let the train run across that!  Maybe even a 1 inch high elevation on each side of the ravine will make  the bridge look cool.

I have no problems with carpentry,  and could plug the hole back up whenever I wanted to.   (I'll keep the cut out section from table screwed somewhere to the underside of the table, so I don't lose it.)

Mannyrock