Transparent Layer of Roads

I'd like to get a layer of roads but have no background so it is transparent. Currently I'm using Stamen Toner but I can't get the background to become transparent. If I use alpha it makes the roads transparent as well which I don't want. Can anyone tell me how to do this with one of the built in layers or a WMS layer I could call that would accomplish this?


I don’t think there is a way to accomplish this using just the built in imagery as none have a transparent background. I think Open Street Map provides a public WMS server that serves roads with layers which you could use: