FLH PDDM Chapter 9 - Eastern Federal Lands Highway Division

9.4.F. Other Design Elements.F. Other Design Elements. Many components go into the preparation of a completed design for a proposedhighway facility. This section will establish basic guidelines and direction for the many elements not alreadycovered but essential to complete the design package. Such elements include culverts, catch basins, curbs,gutters, sidewalks, special ditches and channels, slope protection, erosion control, cattleguards, fencing, etc.1. Highway Lighting. The purpose of highway lighting is to provide illumination for an orderly flow of trafficand to improve road safety during the hours of darkness. Properly designed and maintained fixed roadwaylighting allows the motorist and pedestrian to quickly, accurately, and comfortably recognize all significantdetails in the traffic occupied space.This section provides warrants, standards, and other information on highway lighting installations. Anengineer experienced in lighting design should review all highway lighting designs. Generally, the maintainingagency should be contacted to ensure compatibility in lighting hardware and components.a. Warrants. Lighting warrants relate to the need for roadway lighting and the benefits derived. Factors suchas traffic volume, speed, nighttime road use, night accident rate, road geometrics, and general night visibilityare important when considering highway lighting. Economic returns for lighting are measurable by thereduction in personal injuries, fatalities, property damage, and other societal costs. More effective usage ofthe road and the possible increase in its capacity also affect the warrants.Roadway lighting is warranted for the following:Urban expressways and arterials, urban collectors having ADT (20) exceeding 5000, and urbanintersections having a combined ADT (20) exceeding 10 000.Rural interchanges and intersections where the average number of nighttime accidents (N) per year exceedsthe number of daytime accidents (D) per year divided by three. (Illuminate when N is greater than D/3).Major rest areas located near urban areas or located near available power sources.Tunnels where driver's visibility requirements (or needs) during daylight hours require illumination andwhere the approach roads to tunnels are lighted.Pedestrian underpasses and highway underpasses used by pedestrians.Underpasses on lighted highways.Overhead signs along urban expressways and arterials; and overhead signs at interchanges on roadsapproaching urban areas.b. Design Values. FHWA's Roadway Lighting Handbook gives the levels of average maintained horizontalilluminance and uniformity of illuminance, as well as levels of average maintained luminance and uniformitiesof luminance for various classes of roadways.(1) Urban Intersections. Illuminate intersections of arterials and collector roads with other roads in urbanareas to a level equal to the sum of the illuminance levels of the intersecting roadways. If only one of theintersecting roads has lights, the intersection requires lighting to a level at least 40 percent higher than thelighted roadway.9 - 93