Design Criteria for Adaptive Roadway Lighting

CHAPTER 6. LIMITATIONS AND FUTURE RESEARCH

There are significant limitations to the data collected for these analyses. The purpose of the project was to investigate the impact of lighting on roadway safety and to establish the possibility of reducing lighting on the roadway. This effort focused on interstates and major arterials. Although other roadway types were analyzed, there was a limited number of samples and as a result the statistical power is limited. Several statistical analyses were performed on this data set, including the impact of number of lanes, median type, interchange type, and intersection type. The stratification of the data results in limited sample sizes and limited reliability in the statistical analyses. As such, several of the analyses that were conducted are not documented in this report and are not used as part of the design criteria.

Limitations to the data set include the following:

• Measurements of minor arterials were conducted as part of the routing for the other data collection activities. As a result, very few sites included the minor arterials.
• Specific roadway characteristics, such as median type, number of intersections, and pedestrian levels, were not collected. Rather, this information was drawn from the provided databases, which had limitations to the accuracy of the data and were not consistent across all States.
• The results were analyzed based on the roadway design data that were part of the natural variety of roadway designs encountered as part of the data collection routing. Specific roadway criteria were not sought, which produced an imbalance in the sample size of the resulting data sets.
• As the analyses for these items moved forward, not all the data categories had enough data for stable evaluation of the results. Most of the criteria for selecting the lighting level have been established based on the available literature rather than on specific results of this analysis. This is particularly true for the recommendations for residential and pedestrian areas.

To overcome these limitations, the following future research efforts are recommended:

• Measurement of a significantly larger number of miles and crash data in terms of lighting performance.
• Selection and verification of additional sites in terms of roadway design and geometric features. These need to be included in the database and standardized across States.
• Investigation of additional major arterials and minor arterials.
• Further consideration of residential roadways. These have a significant amount of the roadway lighting in place, and proper consideration needs to be given to these roadways not only in terms of vehicle usage but also for safety and security.
• A research effort that includes weather and atmospheric conditions.