Newman Atkinson says:

A lot of people or clubs use enough space that they can get their hands in-between the tracks to work on a car. Out west these tracks can be that far apart. But what ever scale you use there is little space between cars. As a general rule I will take HO track on straight aways down to 2 inches on center. In the curves I will increase that to 2 and 3/8 on centers to allow overhange from bumping the cars on the other track. Take your longest car with another of the same on the other track to clear each other safely. I use my 86 foot cars because they hang over in the middle of the car and they stick out on the ends into the other right away. The real trains have hang over but usually the curves are not as shallow as our model trains and really don’t hang out as much as our model counterparts. Put a model person between the trains and that should be close to either car. The real tracks don’t usually have too much extra space between trains. I don’t recommend going out on the real one to find out. it can be close. Just adjust the N scale rule from what I use on HO. To do this on any scale, If you add switches, some of the ready made switches have motors already mounted on the switch. and you will have to adjust for them. But if you use underneath motors them you don’t have to worry about the track clearance required for those.Happy track laying. The clearances are much more real. Newman

Garth says:

Go to this site for the official distances. http://www.leg.state.nv.us/nac/NAC-705.html It states 14 feet between parallel tracks. For N scale this equates to 26.67mm. This is too tight for curves on a model railway where radii are a lot tighter than in real life. I use a spacing of 28mm which is also the distance obtained when using Peco turnouts for cross overs.