I've been working on my own layout lately and I'm at the point where I'm ready to start working on detailing some paved streets. A big part of that detailing involves common traffic road signs and pavement markings. In real life, we drive by or over them every day. But when I started thinking about painted street markings, I realized that I had no clue as to what their dimensions were, or any other standards for that matter.
Thank goodness for the internet! I did some searching and came across this website by the US DOT Federal Highway Administration: the Manual on Uniform Traffic Control Devices (MUTCD). It has many of the standard configurations for traffic signs and pavement markings, including those for rail grade crossings, which is very important for model railroads.
So get your scale conversion calculators out and start working on traffic control devices for your layout!