Page 10 of the Rice Signs 2017 Traffic Safety Catalog covers five families of regulatory signs used on highways and toll roads. The Passing Zone signs include R4-1 Do Not Pass, R4-2 Pass With Care, and R4-16 through R4-18 Keep Right Except To Pass. Slow Traffic signs include R4-3 Slow Traffic Keep Right and R4-5 and R4-6 Trucks Use Right Lane signs. The Headlight Use Signs (R16 series) instruct drivers to use headlights in sections such as tunnels, bridges, or designated safety zones. Roundabout Signs (R6-4 family) mark circular intersections and include the R6-5P yield-to-circulating-traffic plaque. Pay Toll Signs (R3-28 family) mark toll plaza approaches with distance and exemption plaques.