Atlas-O Crossover with High Speed #7.5 turnout

Personally, I believe it would be nearly impossible to do what you suggest without seriously compromising operational fun (lot of derailments).  You could try using either the Atlas #5 switches (shorter run length) or Ross #4 switches (even shorter run length).  Might have to slow the "high speed" run rate a bit, but will work much better than trying to mix a #7.5 with any curved, toy-train like (O72, O81, etc.) switch.

Chuck

I concur with PRR1950. You're looking at operational problems using a curve-replacement turnout for "high-speed" crossovers. The #5 is soft enough for reasonably high speeds, but if you have the 49" available, a pair of #7.5's would look better and allow for higher speeds. Either the #5's or 7.5's will give you 4.5" track spacing.

Not nearly impossible, it IS impossible. The diverging leg of an O-whatever switch is a replacement for a curved section of track. The diverging leg of a numbered switch is a tangent. It functions essentially as straight. So whereas an O-72 for example is 22.5 degrees of a circle, a #7.5 is around an 8 degree divergence from straight. They cant go together on parallel tracks. 

Ross switches are shorter than atlas ones. You can cut a Ross regular (essentially a #5) down to about 12.5" if you need to. We use the regulars on modules all the time and fly through them. If you want a little more ease, bump up to a ross #6. 

I would also recommend using a pair of #5 Atlas switches if you have enough room. I have one on my layout and I am very happy with it. My rolling stock actually goes through the #5 switches better than the #7.5s.

johnf posted:

I would also recommend using a pair of #5 Atlas switches if you have enough room. I have one on my layout and I am very happy with it. My rolling stock actually goes through the #5 switches better than the #7.5s.

I'll second this. Our whole layout is all Atlas O track and turnouts, with all the crossovers being #5s. Another disadvantage of those VERY LONG Atlas #7.5s are, most locomotives will not maintain electrical contact through the turnout, due to the large spacing between the hot center rails. Even with my #5s, I had to add an additional electrical pick-up roller assembly on the tender of one or two steam locomotives. 

You could try either the Ross #4 Double cross over, it is about 32 inches long, or two #4 turnouts (with a 3 inch straight in the middle to get about 4.5 inch track center) though they probably will not accommodate fast moving trains . The #8 is more appropriate but it is as long as two Atlas #7.5

Joe