If you were building an HO layout I could
direct you to where you can buy 'girder rail',
but as an N modeller you'll have to make your
First, girder rail has an extra section with the
flangeway molded in. This prevents the
pavement from oozing into the flange area.
You can make your own, but it's gonna be
work. Strip rails out of your N flex track. Solder
the HEAD of a length to the inside of both
track rails. The bottom of the soldered on rail
will form the flangeway.
Or if you can find a metal, plastic or even wood
strip the height of your track rails, it can be
soldered or glued in such a way as to form
the flange way.
You can then use whatever you plan to pave
your streets with and level it with the top
of your track rails, making certain to keep
the flangeway clear as you would at a crossing.