This report documents a Federal Highway Administration (FHWA) project to identify potential improvements to current signing practices for complex interchanges. Based on the initial literature review task along with discussions on other ongoing work, FHWA and the research team divided the project into the following two studies: (1) conduct a driving simulator study and (2) develop a metric or tool that can score, rate, or otherwise categorize interchange complexity. In the first study, test signs were introduced as six topics in a simulation along freeway roadways to evaluate drivers’ real-time response to the signs. Topic 1 tested the understanding and use of different methods to sign for an option lane. Almost all participants made the correct decision to exit or stay on the freeway; however, many unnecessary lane changes were made with each of the three sign sets (SSs). Topic 2 studied sign methods when two interstate exits were within close proximity and a need existed to sign for three destinations (two interchanges/exits and the through lanes). For the SS that had an arrow-per-lane design, all participants made correct lane change decisions. Topic 3 evaluated signing for an upcoming exit that had a Y-split into two directions. While several incorrect lane changes were made for each SS, the SS that used split exit signs at all three sign bridge (SB) locations had the fewest incorrect lane changes and was judged superior in comparison to the other two arrangements. Topic 4 evaluated whether it was better to fill an advance single sign with supplemental way-finding information or to spread the information among multiple signs. An observation from this topic was that spreading information about the next exit across multiple signs on a single bridge may have unintended consequences if the SB also includes a sign for another exit that is located to the left of the preferred lane. Topic 5 evaluated the effectiveness of sign spreading when there were many pieces of information on one SB. Similar to topic 4, it was determined that the lateral position of a sign on the SB is important. Topic 6 evaluated driver understanding of left exit signs. The difference between the two SSs that were tested was minimal. In study 2, the complexity rating tool focused on geometric design factors and related effects on driver expectancy and driver workload. After several revisions, researchers settled on a spreadsheet tool that considered the effects of 32 weighted factors that were based on site characteristics. To determine how well the spreadsheet tool would evaluate interchanges, the research team used the spreadsheet to review 28 existing sites in 11 States. The sites were submitted by State transportation departments based on their perceived complexity. For the characteristics included in the spreadsheet, the results provided a general sense of the relative complexity of the interchanges studied. (Author/publisher)
Samenvatting