Collecting and Analyzing Stakeholder Feedback for Signing At Complex Interchanges

CHAPTER 4. CONCLUSIONS

The findings from these stakeholder activities led to several conclusions that address the objectives of the project, plus some additional findings. These findings include the following:

• Stakeholder's conception of and experience with complex interchanges.
• Aspects of complex interchanges that cause problems for drivers.
• Recommendations for future human factors research based on stakeholder information needs.

Each of these conclusions is described below.

STAKEHOLDER'S CONCEPTION OF AND EXPERIENCE WITH COMPLEX INTERCHANGES

Almost all stakeholders had direct experience addressing problems associated with complex interchanges, and approximately two thirds of them have to address problems with these interchanges on a yearly basis. When stakeholders were asked what makes an interchange complex, most did not have a specific definition. Rather, they tended to mention characteristics of interchanges that make navigation more challenging for drivers, even leading to higher crash rates in some instances. The key characteristics of complex interchanges include:

• System interchanges.
• Multiple/successive option lanes, splits, or exits.
• Short weaving sections.
• Collector-distributor roadways.
• On-ramps and off-ramps for HOVs and managing/signing access.
• Providing a lot of information to drivers at one time.
• Unfamiliar sign/marking elements.
• Lack of lane balance leading to forced merges.
• Unexpected maneuvers/violations of driver expectations.
• Horizontal/vertical alignment of interchange.

A trend that emerges from examining these characteristics is that complex interchanges often involve multiple routes that converge or diverge within a short distance, resulting in geometric or signing elements that ultimately cause higher workload for drivers in addition to a scenario that departs from drivers' mental models and other expectations. Requiring drivers to analyze a lot of information, make many decisions, and execute multiple maneuvers in a short period of time seems to cause problems, especially if those elements are not routine (e.g., unexpected maneuvers, determining where a lane goes, viewing unfamiliar symbols). This finding is consistent with the results obtained in a previous project that that examined this question from the driver's perspective.⁽²⁾ Moreover, one outcome of that earlier project was the development of a basic task analysis approach for quantifying drivers' perceptual, cognitive, and psycho-motor loads across specific interchange maneuvers. There may be some value to developing that approach into an early-screening tool that can be used by engineers to identify interchange designs that could be overly complex.

ASPECTS OF COMPLEX INTERCHANGES THAT CAUSE PROBLEMS FOR DRIVERS

Stakeholders identified several common interchange elements that seem to routinely cause problems for drivers. These driver problems included: increased crash rates, traffic delays, information overload, missed exits, and complaints from drivers about poor route guidance and insufficient time to make decisions and lane changes. Some of the interchange characteristics that cause the most problems for drivers include the following:

• Closely spaced ramps and interchanges.
• Short weaving sections.
• Collector-distributor roadways.
• Signs for certain lane movements, including option lanes, exit-lane splits, lane drops, and left exits.
• Control destinations on guide signs.
• Signs with many information elements that lead to information overload.

CONSDERATIONS FOR FUTURE HUMAN FACTORS RESEARCH BASED ON STAKEHOLDER INFORMATION NEEDS

A key finding from the interviews is that stakeholders see value in conducting additional research on human factors issues at complex interchanges. In particular, stakeholders reported that they have to deal with problems at complex interchanges on a regular basis, and most of them provided specific examples of human factors challenges that they had to address at a specific complex interchange in the past. A common view among stakeholders is that they have insufficient guidance and supporting design information to identify specific and effective solutions, or suitable design alternatives to address problems at interchanges. On a related note, many stakeholders mentioned at some point during the interview that they have a strong desire to see consistency both within their State and across States. Following the MUTCD ensures some degree of consistency, but stakeholders lack similar reference information that they can use to address the broad range of driver problems they regularly encounter at complex interchanges.

The combination of the stakeholder interviews with the follow-up survey provided a good understanding of the priorities for future complex interchange research. The priority level of a topic was determined by the rank, as shown in table 4. The topics that received the highest priority ratings generally focused on signing requirements and the distribution of guidance information on the roadway. The top-rated research topic was related to APL sign requirements (see table 5). This is perhaps not surprising, given that this topic has received a lot of attention due to recent changes in regulations. Some of the interest may be attributable to those recent changes. There also, however, seems to be a disconnect between what is a desirable design for APL signs and what is seen as feasible from the States' perspective.

Table 5 . Highest priority research topics based on
stakeholder feedback in the survey.

The next three highest ranked topics all related to the distribution of information on the roadway, including: guide sign spacing requirements, the information limit per guide sign, and the application of pavement markings that include navigation guidance. These three topics consider three aspects of information layout, particularly in dense areas where a lot of navigation guidance can be presented to drivers at the same time. It may make sense to study these related topics in conjunction with one another, as part of the same research project. Guide sign spacing and the information limit per guide sign both relate to Federal guidance (e.g., MUTCD) that can be difficult to follow in some situations. Pavement markings differ in that there is a sense that they provide a useful approach to providing information to drivers; however, there is less guidance available as to where and how they should be applied. All three of these topics would likely be studied in an urban environment, where there is a high density of exit ramps, interchanges, and/or destinations to sign. The countermeasures found during these studies would be implemented to improve driver navigation by redistributing navigation guidance in areas where the information density is high.

In addition to the research needs listed in table 5, stakeholders also identified a wide range of other issues involving human factors for which they would like to see more research conducted. These topics were also evaluated in the follow-up survey, and they are listed as follows in alphabetical order:

• Algorithm for justifying the cost of roadway construction projects to drivers.
• Control cities on guide signs.
• Develop additional design examples.
• Diverging diamond interchanges.
• Organization and number of route shields.
• Signing for collector-distributor roadways.
• Signing for exit-lane splits.
• Two-lane flyover ramps.

It is clear from the stakeholder feedback described in this report that complex interchanges pose an ongoing challenge to roadway engineers and State transportation department personnel. Previous projects have begun to identify human factors issues that can lead to driver stress and errors when navigating these interchanges. However, there is no simple definition or single prototype example of a "complex interchange," and a variety of geometric and signing elements can make different interchanges complex and difficult for drivers to navigate. Consequently, the human factors problems that drivers can face at these interchanges also vary greatly; this is reflected in the wide range of research needs identified by the stakeholders. It is also clear from the interviews and survey that stakeholders have many unmet information needs and other questions related to complex interchanges. They also see value in additional research and corresponding design guidance that would address these information gaps.