VDOT and other highway agencies have explored lighting changes in the past. Many state departments of transportation are searching for ways to be more energy efficient while maintaining a transportation system that is safe, facilitates movement of people and goods, and improves the overall quality of life of citizens. Local budget shortfalls, overall economic downturns, upward trends in energy costs and increasing concern for the environmental impact of highway operations are driving state departments of transportation and similar agencies to reconsider current practices in roadway lighting. Such changes have been considered before, typically during difficult economic times or times when the cost of energy has risen unexpectedly, starting with the Oil Embargo of 1973-74. In fact, VDOT has explored the issue from conservation, safety, and risk assessment angles ... The purpose of roadway lighting is to provide improved safety, security, and aesthetics for the various users of the roadways and associated facilities (including bridge and tunnel lighting, sign lighting, roadway delineation and even parking facilities). AASHTO's Roadway Lighting Design Guide, (October 2005, p. 7) cites National Highway Traffic Safety Administration (NHTSA) crash data as showing that "90 percent of fatal and injury crashes occur the roadway, where lighting guidelines specify that light be placed, are multiple vehicle crashes. The number of overall crashes tapers off substantially after midnight on weekdays and after 4:00 a.m. on weekend. At these late hours, most of the crashes are single vehicle, off-roadway crashes for which lighting may not be likely to help, except possibly at decision-making points such as ramp gorges, intersections, and merge areas." AASHTO's guide notes that crash rates increase where lighting systems are turned off or where every other luminary is turned off. Dimming or "lighting curfews" may be less likely to result in increased crash rates. Still, in an effort to save money, many agencies periodically consider altering the way they light roadways. Some options for reducing energy consumption related to roadway lighting include: Solar-powered lighting for overhead highway signs or in other standalone applications; Lighting spaced farther spaced, or the "every-other-luminary" technique; Reducing the overall amount or level of continuous roadway lighting; Replacing traditional lighting elements with energy efficient elements (namely LED lights); Increased lighting curfews or "incremental dimming" of roadway or sign lights; Using more highly retroreflective of signs or safety markings or experimenting with electroluminescence or photoluminescence; Using sensors or other advanced technologies to automate lighting in a more precise way. "During the past decade, several highway agencies have switched off roadway lighting during periods of energy shortages to reduce maintenance and operating costs. However, quite often such lighting was restored when nighttime accidents increased. One fundamental problem with such light reduction techniques was that lighting was reduced or eliminated during the entire nighttime period, rather than only when traffic volume was low. By providing full lighting during periods when volumes are high and the roadway operated near capacity and providing reduced lighting as the traffic decreases, the potential exists for realizing considerable energy savings while still providing the benefits of full lighting at key locations (i.e. intersections) and at key times (i.e., high volume) where driver decision-making is the most critical and the greatest visibility is required." (Roadway Lighting Design Guide, October 2005, p. 7).