Principles and Guidance for Presenting Active Traffic Management Information to Drivers (2021)

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101 Chapter 6: Conclusions Taken together, the activities conducted in this project provided information to address the key research gaps. This section summarizes each key research gap and lists the study information that applies to each gap. Note that some of the research questions were addressed at a high level for practical reasons, which resulted in the findings applying to multiple gaps. Accordingly, research gaps 1 and 2 share the same information, as do gaps 5 and 6. Gap 1: Some DMS with a message about “low visibility” or “slow traffic ahead” can alert drivers to the need to reduce speeds generally, while dynamic speed limit signs can diminish the variability of the reduced speeds by providing a specific number. Dynamic speed limits are sometimes deployed as a standalone system or do not contain a message about why there is a reduced speed in place, and lack of driver understanding about the meaning of the signage can hinder its effectiveness. Does the provision of additional information as an explanation to justify and encourage travel at reduced speeds—e.g., “low visibility” or “congestion ahead” via supplemental DMS or dynamic elements–increase the effectiveness of a dynamic speed limit, measured in terms of better speed compliance and lower average speed? (Q1 or Q230) • The study findings related to research gap 1 are covered in the findings related to research gap 2 below. Gap 2: Locations differ in the provision of static signage in advance of an ATM deployment with lane control signage, one example is shown in the photo below. This may be done for legal reasons for enforcement purposes; as a condition in the legislation allowing the deployment of a new strategy such as dynamic speed limits or a dynamic shoulder lane that is a change from current practices; or simply for informational purposes to help drivers understand. Is there a benefit of increased driver understanding in providing static signage in advance of ATM deployments to explain symbols? (Q1) • In Experiment 1, participants experienced provisional signs before entering the dynamic speed limit zone, and post-experiment survey asked participants to rate effectiveness of the provisional signs. The results showed that around 72% of the participants thought the reduced speed zone signs before the dynamic speed limit signs increased the effectiveness of the dynamic speed limit application based on their driving in the simulator. Also, we asked participants to rate three aspects of provisional signs (importance of the intended purpose, effectiveness, and ease of understanding) in general (not limited to the application they experienced in the simulated driving). Results showed that participants perceived the provisional signs as (a) moderately to extremely important (77%), moderately to extremely effective (91%), and easy to very easy to understand (84%). Gap 3: Dynamic information can be disseminated to drivers using various media, whether agencies provide information for drivers via infrastructure, to vehicles for in-vehicle messaging, to third-party providers for smartphone applications, or a combination of these approaches. 30 These notations (Q1, Q2, etc.) refer to which of the 6 original research questions the individual research gap is associated with.

102 What media is the best for disseminating dynamic information to satisfy driver wants and needs? (Q1, Q3) • The results from the post-experiment questionnaires showed that drivers who participated in Experiments 1 and 2 preferred to receive ATM information through infrastructure-based ATM media. Around the half of the participants selected infrastructure-based ATM media as the most preferable media type in Experiment 1 and around 70% of the participants selected infrastructure-based ATM in Experiment 2. A combination of infrastructure and smartphone-based ATM media was ranked as the 2nd most preferred ATM medium. Interestingly, not many participants preferred either a smartphone or an in-vehicle display as a sole source to receive ATM information. Participants in this study were also asked their preferred ATM medium for different ATM applications. For variable speed limit, lane signaling, and junction control, about half of the participants preferred infrastructure-based ATM strategies and the other half of the participants preferred a combination of infrastructure-based ATM strategies and either a smartphone or an in-vehicle display. However, for ramp metering, about 66% of the participants preferred infrastructure-based ATM and the participants showed relatively less interest in alternative media for this application. Gap 4: Dynamic information can be disseminated to drivers using various media, whether agencies provide information for drivers via infrastructure, to vehicles for in-vehicle messaging, to third-party providers for smartphone applications, or a combination of these approaches. What media for disseminating dynamic information achieves the lowest driver distraction, highest driver understanding and usage, and largest safety and mobility benefits? (Q2, Q3, Q4) • Although the data collected from this study only partially addressed all aspects of this question, the potential for driver distraction due to using smartphone as an ATM medium was examined, based on eye-tracking data and survey results. The results from Experiments 1 and 2 showed that none of the experimental conditions that disseminated ATM information from both the overhead gantries and a smartphone, significantly increased either total glance time or average glance duration to the smartphone, compared to the present-day application (the gantry-only condition in both experiments). Also, none of the experimental conditions were above the AAM’s distraction criterion (2-seconds). However, when the ATM information was disseminated only from the smartphone, drivers’ total glance time and average glance duration to the smartphone increased. As mentioned before, the level of distraction observed in this study is far below what we usually consider as driver distraction in HMI studies. The survey data also supported the finding that the smartphone application in this study did not distract drivers to an unacceptable degree. However, this finding, while preliminary, suggests that types of ATM media and the combination of multiple ATM media can affect drivers’ glance behavior and their distraction in future applications. Gap 5: As an alternative to deploying and maintaining a sign over each lane, a single dynamic message sign might present similar dynamic lane control information in the form of a pictogram.

103 Are lane closure pictograms on a DMS understood by drivers, and are they equally or more effective than information presented via overhead dynamic lane control signs? (Q4) • The study findings related to research gap 5 are covered in the findings related to research gap 6 below. Gap 6: In order to reduce the costs of deploying and maintaining ATM infrastructure, some agencies are considering alternatives that require less dynamic signage, which may use messages on DMS instead of overhead lane control signs or longer-distance intervals between gantries. Can dynamic information traditionally presented on lane control signs with supplemental DMS be presented on less signage in an equally or more effective manner? (Q4) • The survey for comparison of DMS, overhead signs, and pictograms in Experiment 2 asked participants’ opinion on three different types of signs (overhead signs, DMS, and pictograms). Participants indicated that DMS and overhead gantry signs were almost equally effective, but pictograms were less effective. This pattern was consistently observed in the subsequent question, which asked participants to rate clarity of communication for each sign type. Also, results showed that participants rated the overhead gantry as the most effective way to disseminate the ATM information among the three options. When combinations of multiple sign types were allowed, participants rated “overhead gantry with DMS” as the most effective media. As observed in the first part of this survey, pictogram was rated as the least effective medium. Gap 8: Is there a way to accurately quantify mobility-related benefits of an ATM deployment, or the safety-related benefits of a temporary ATM deployment? (Q5) • This gap was addressed with the outreach activities. Most ATM deployment evaluations focus on travel time and delay measures to quantify mobility benefits, although mobility is not always considered since it can be challenging to quantify or may not be a focus of all ATM deployments. Evaluation approaches vary from a relatively simple before-after calculation of trends or statistical analysis of data to more complex modeling methodology or video analysis. Multiple evaluation reports are available to review methodology and findings in greater detail. Respondents with temporary ATM deployments noted the difficulty of evaluating work zone deployments due to the short-term duration and different conditions for each location, and only limited, anecdotal examples are available. Gap 9: How can agencies systematically weigh the various criteria associated with mobility, safety, cost, and driver needs when considering the deployment of ATM strategies? (Q6) • This gap was addressed with the outreach activities. Many respondents struggled with defining how their agency balances these criteria, with some interviewees saying they were not sure that their agencies fully understand “driver needs.” Survey respondents gave varying replies, with nearly all agencies considering both mobility impacts and safety impacts for all types of ATM strategies, a large majority considering costs for all types of ATM strategies, and most considering driver needs for at least one type of ATM strategy.

104 Gap 10: Given a situation where multiple ATM media are available, what information do drivers want/how do drivers want to receive the information/when do drivers want to receive the information? (Q1) • First, across all four applications (variable speed limit, ramp metering, lane signaling, and junction control), over a half of the participants preferred infrastructure-based ATM media. Especially, for the ramp metering, around 66% of the participants preferred infrastructure-based media. Second, only a few participants selected in- vehicle displays as the most preferred ATM medium. Third, another half of the participants preferred combinations of infrastructure-based media and either smartphone or in-vehicle displays. This finding may raise the possibility of drivers’ needs for alternative ATM media to supplement the infrastructure-based media. Gap 11: For the alternative ATM media such as smart phones and in-vehicle displays, ATM information can be delivered by multiple modalities (e.g., auditory messages, visual messages, or combination of two). Given a situation where multiple ATM media are available, what would be the most efficient and the least distracting modality (or modality combination) to deliver ATM information for the alternative/innovative ATM media? (Q2) • Experiment 2 results showed that the visual information mode, which presented dynamic speed limit information only visually (with symbols), led to longer total glance times to the smartphone compared to the present-day application. However, when the smartphone presented the same information in an auditory-visual way (with symbols and audio messages), it did not add extra visual demands compared to the present-day application. Further examinations will be required to generalize the findings in this study, but the results of this study, at least, suggested the use of auditory messages along with visual information for displaying dynamic speed limit information. Gap 12: In the previous research, none of the reviewed studies deeply addressed integrated applications where both traditional ATM and alternative media (e.g., in-vehicle displays) are employed together. In a situation where multiple ATM media are deployed (e.g., electronic signs and in-vehicle displays), should they deliver the same information? Or should each medium need to play a specific role to compensate each other and to avoid redundancy? And what will be the best way to harmonize multiple ATM media (including traditional and alternative media) and how are we to evaluate the effectiveness/efficiency? (Q3) • Experiment 1 investigated the effects of information availability. Two experimental conditions were manipulated. The “just-in-time” mode disseminated the ATM information at the same time that drivers could see the information from the overhead gantry, whereas the “always-on” mode disseminated the information sooner than the overhead gantry did. Participants’ percentage of time in merge/close lanes was significantly lower when they received the lane closure information from both the smartphone and overhead gantry, compared to the present-day gantry-only application. When the ATM information was available from both the smartphone and overhead gantry, there were no significant differences between the always-on and just-in-time mode in terms of percentage of lane compliance. However, in terms of

105 participants’ preference measured by the post-experiment survey, the majority of the participants (70%) preferred the always-on mode over the just-in-time mode. The research activities conducted in this project provided actionable information pertaining to several of the research gaps. However, because the studies targeted a broad set of research gaps, the resulting information does not address each research gap completely. Moreover, for some research gaps, such as those pertaining the implementation questions, the research yielded insufficient information to provide partial answers. Overall, ATM information dissemination is still an emerging topic that requires further research to establish best practices. Nevertheless, this project made significant strides towards framing the research gaps and addressing some of those information needs.

106 APPENDICES