Roadway Visibility Research Needs Assessment

4. Best Practices

In a review of current practices, some states and agencies emerged as leaders in the application of visibility treatments. A summary of the state practices for lighting is shown in Appendix B.

In terms of lighting, many states have moved significantly forward with the application of new lighting technology. Many states have developed a specification for solid state luminaires, including Virginia DOT, Illinois DOT, and Alaska DOT. These states have been sharing their results, and some similarity is being found in their specifications. This is an important step in the implementation of the new technology because LED luminaires are significantly different in their applicability to the roadway than are the traditional solutions.

From a city perspective, some municipalities are implementing adaptive lighting systems. These include the City of Cambridge, Massachusetts, and the City of San Jose, California. In both of these cities, lighting is dimmed based on the time of day. This practice has been implemented as both a cost-saving method and as an effort to reduce the negative impacts of lighting on the environment and roadway users.

Another implementation of a lighting control system is the use of the system to accurately provide a lighting level on the roadway regardless of the wattage and the power usage of the luminaire. Hawaii is using the same luminaire in all applications and then dimming to the appropriate lighting level. This approach significantly reduces inventory and maintenance costs while continuing to provide the recommended lighting levels.

Some cities, like the City of Los Angeles, are using the data-carrying capabilities of the lighting network to provide a backbone for connected-vehicle and smart-city applications.

Based on the assessment of the agencies, the best practices are (in order of technical complexity):

1. Development of a specification solid state lighting specific to the roadway types and needs of the lighting network.
2. Implementation of a control system where each luminaire is able to be managed from a central location.
3. Implementation of lighting only when and where it is needed through crash analysis and updated warrants.
4. Implementation of an adaptive lighting system based on the time of day.
5. Implementation of an adaptive lighting system based on road conditions, user needs, and connected vehicles.

While many agencies are working on some aspect of each of these approaches, no single agency has achieved the highest level of implementation.