=>Does 7ft sound to wide, how do you work out what the radius should be, given =>the fact that I'm not running any long equipment eg, running with box cars, =>tanks, coal cars, & mainly older style diesel engines bought 2nd hand off =>other railroads & just because I can, any train that has to stop or back up =>on the main line due to switching is to have a caboose (Yah)!. =>
=>You wouldnt believe how much fun I am having doing this..:)
The NMRA suggests 24" radius for cars and locos up to about 60ft in length. In a 7ft wide peninsula, you can have a curve of 36-38" radius, so your trains will look very nice. Such a radius also leaves plenty of room for sidings inside the curve. You should leave a space of 4" or more between the track and the edge of the layout for safety - reduces the odds that a derailed train will fall to the floor. Also reduces the odds that someone's careless elbow will bump the train. If you must have a narrower space, fasten strips of clear plastic aliong the layout edge to protect the trains.
You will also need some sort of access to the insde of the peninsula, as you cannot reach into it very well. Tables/shelves should be 2ft wide or less between edge and backdrop for comfortable and safe reach. They can be up to about 3ft -- but that extra 12 inches or so may put something just out reach without leaning on the layout, which may cause some, er, geological disruptions.:-) In your case, I would build the peninsula hollow, that is, put up the backdrop 2 to 2-1/2 ft from the edge. This will leave an internal space of 2-3ft wide. The alternative would be to build a number of removable scenery sections so you can pop up inside the layout for maintenance, etc.
Enjoy!