I can't see exactly where your 3rd street industrial area is but most prototype railroads avoid runarounds if at all possible. I have a point to point switching layout and I don't use runarounds. I handle the trailing point switches on the way out and on the way back handle the trailing point switches that were facing point switches when I was heading out. Once I turnaround they are now trailing point and I don't need to run around the train. Just my 2 cents.

David:

I suggest that you draw this plan with either Xtrkcad or SCARM (both free) to get a better idea of how your plan will really work . I assume this is N scale since you only have 5' of width to work with. With the double crossover on the left and bridges on the right, you will have extremely sharp radius curves.

Howard

Looking at your design I see one thing that jumps right out at me. The exit from the main line in the bottom right goes across a crossing. In my opinion the grade from the crossing down to get the clearance to go back under the main line is going to be way too high.
I would suggest removing this exit from the main line and then there. Would be a "branch line" running from federal st. to 3rd st.
The other thing and this is my opinion of what I like to run on is that the two track main line without any staging or destination would bore me to tears in a week. Do you have any potential space that can be used as staging. With the right backdrops, or well placed buildings even the 5ft. wide side could offer some change in power and rolling stock.
just my opinion....

You bring up a great point. Looking at it the first time it looked like an n scale plan but after re reading David plans code 83 s rail so that means HO scale. Like Howard said the first thing you should do is really get a copy of a software design program or if you don't want to go that route a piece of graph paper. The design should be scaled out properly if you want it to be a success.

I agree with Cadmaster on the Grade.  It appears to be pretty steep in that section. I'm not sure how much operational intrest it adds to have the mainline exit at that point anyway. freeing that up might add some space for another industry on the branch.

You might consider longer sidings as well, otherwise, I think it's a good start!  I like how the branch runs below the main on the right.  That should look very dramatic when completed.

All great comments. I need to be more clear. 1) The plan is HO and drawn with SCARM but it is my first time using it and, as stated, a bit rough. 2) the over all size of the layout is 5' long on the ends and 30 " wide and the sides are 12' long and 30" wide. Essentially a large rectangle with a large rectangle inside. 3) Both track plans copied are 10' long (which should fit on the long sides) and 2' wide which gives me an extra 6" of depth. 4) I agree that an adjustment in terrain could give me "underneath" staging tracks. 5) Hopefully a 10' plan on a 12' run would allow for more gentle curves.

Once I get the hang of the drawing program, I believe I can clean up the drawing and modify it to include staging. I want this to be right so your comments are much appreciated, I need to check the Industrial plan again to see what the gradient is. Is 3" a correct height for a train to pass under a bridge?

David, This is the actual size of Federal Street that I copied from an image taken off line. the Red box is your 12' x 5' space (table top) As you can see this will be hard to fit into this space in HO scale. The only 3rd Street Track plan I could find did not have dimensions so I did not attempt to do that. 

the over all size of the layout is 5' long on the ends and 30 " wide and the sides are 12' long and 30" wide. Essentially a large rectangle with a large rectangle inside.

Also the dimensions you are giving sort of don't add up to the rectangle inside. 30" + 30" = 60" = 5'