How do I weather my roads?

Well I got my roads down and was wondering on what/how to weather them. I was thinking on using powders or greese. Is there a better way? I kinda know where to weather. Mostly by my factory doors, truck terminal, under my over-head carne, and by my grain elevator. I was also wondering, Would it be weathered darker on the out side of the road, and lighter in the middle?

EDIT: They are concrete roads.

The blacktop roads around here are darker in the middle of the lane. I guess from engine oil leaking from the cars.

Edit-found this.

http://www-personal.umich.edu/~aleskiw/roadgeek/Gallery9a.htm

You can see the difference between blacktop and concrete.

I just paint my roads concrete gray then spray them with a mix of alcohol and black leather dye.

I forgot to mention they are concrete roads.

Go to Michaels or any art supply store and buy powdered Tempra paint. Black and White is all you need. Dry brush it on and mix the colors.

I found some sticks of charcoal such as artists use. I very lightly scratched a line on each side of the road and then used an old mascara brush* to smooth out the solid black line so it blends in with the rest of the road, which I had earlier painted grayish/khacki tan to look like concrete. The spray painted surface has the right kind of “tooth” to hold the charcoal. Where it seemed a bit too dark I used an old toothbrush* to wipe it almost clean. I then used Dull Coat to seal the charcoal. But warning – if you use a Sharpie to draw in the lines where tar is used to seal cracks, Dull Coat makes the Sharpie ink dissolve and run. I had already drilled holes for the Walthers manhole covers, and notched the sides for the Walthers drains.

Dave Nelson

*Make sure your wife/mother/sister/significant other know that any kind of brush they use is something you want when they are done with it. Frankly almost every week most people throw out stuff that model railroaders could use.

Hooray for this question AND the replies, many layouts have great scenery and these shiny black roads like they were just paved, glad to see questions like this.