Novel time-delay side-collision warning model at non-signalized intersections based on vehicle-to-infrastructure communication
In complex traffic environments, collision warning systems that rely only on in-vehicle sensors are limited in accuracy and range. Vehicle-to-infrastructure (V2I) communication systems, however, offer more robust information exchange, and thus, warnings. In this study, V2I was used to analyze side-collision warning models at non-signalized intersections: A novel time-delay side-collision warning model was developed according to the motion compensation principle. This novel time-delay model was compared with and verified against a traditional side-collision warning model. Using a V2I-oriented simulated driving platform, three vehicle-vehicle collision scenarios were designed at non-signalized intersections. Twenty participants were recruited to conduct simulated driving experiments to test and verify the performance of each collision warning model. The results showed that compared with no warning system, both side-collision warning models reduced the proportion of vehicle collisions. In terms of efficacy, the traditional model generated an effective warning in 84.2% of cases, while the novel time-delay model generated an effective warning in 90.2%. In terms of response time and conflict time difference, the traditional model gave a longer response time of 0.91 s (that of the time-delay model is 0.78 s), but the time-delay model reduced the driving risk with a larger conflict time difference. Based on an analysis of driver gaze change post-warning, the statistical results showed that the proportion of effective gaze changes reached 84.3%. Based on subjective evaluations, drivers reported a higher degree of acceptance of the time-delay model. Therefore, the time-delay side-collision warning model for non-signalized intersections proposed herein can improve the applicability and efficacy of warning systems in such complex traffic environments and provide reference for safety applications in V2I systems.
Principles and Guidance for Presenting Active Traffic Management Information to Drivers
Active Traffic Management (ATM) strategies have become more common in the United States as State departments of transportation (DOTs) grapple with increasing congestion and fewer dollars available to add capacity to keep pace. ATM strategies provide a more cost-effective solution to better manage traffic using the available capacity of the existing roadway network. The expansion of ATM strategies and implementations has led to a concurrent increase in the options available to deliver ATM information to drivers. Information displays designed to capture drivers’ attention quickly include devices that vary in terms of whether they are: fixed and moveable, graphics-based and text-based, overhead and roadside, as well as handheld and vehicle-based. Because of the innovative nature of ATM strategies, there is limited guidance available and many research questions remain about how ATM information can be effectively and safely presented to drivers across the many existing and potential dissemination methods. The objective of this project is to develop principles and guidance for presenting drivers with dynamic information that can be frequently updated based on real-time conditions. These principles and guidance should improve the effectiveness of ATM strategies, which include systems to manage congestion, incidents, weather, special events, and work zones. The project is intended to explore and provide answers to the following six key research questions: 1. What information related to ATM strategies does a driver want and need? What characteristics are associated with this information (e.g., reliability, timeliness)? 2. How much information can a driver process via the complementary and contrasting modalities (e.g., visual, auditory), given the context and distractions? 3. What existing and potential media could be used to deliver this information? Media that are under the control of transportation agencies (e.g., electronic signs) are of primary interest but alternative and innovative media (e.g., in-vehicle displays, cell phone applications, geographic information systems) and their evolving capabilities and roles must be examined. 4. Given a particular message and medium, what are effective ways to prioritize, format, and present the information to achieve a desired and safe response by drivers? 5. How can an agency evaluate the return on investment of an ATM infrastructure or information technology decision? 6. How can an agency balance the needs of drivers and infrastructure costs, including maintenance and operations? This project involved two broad phases to achieve its goals. Phase 1 (Chapters 2-4) primarily involved documenting the ATM state of the practice and reviewing critical literature, with the goal of specifying the detailed requirements of the Phase 2 research and analysis activities. Phase 2 of the project (Chapters 5-6) involved original research and data analysis to inform the development of a series of deliverables including guidance and principles for agencies and third-party providers on the presentation of ATM information to drivers. This report is divided into six chapters: Chapter 1 – Introduction: This chapter provides a general overview of the project objectives Chapter 2 – State of the Practice: This chapter documents the state of the current practice of displaying ATM information both within the United States and internationally Chapter 3 – Literature Review: This chapter synthesizes the available literature about displaying ATM information in key topic areas and identifies research gaps within those topics Chapter 4 – Research Gaps: This chapter describes activities related to refining and prioritizing research gaps related displaying ATM information Chapter 5 – Empirical Studies: This chapter describes the methodology and findings for three studies that were conducted during this project to address the key research gaps Chapter 6 – Conclusions: This chapter integrates the available information about each research gap developed across all project activities To develop principles and guidance for presenting ATM information, different activities were conducted in both qualitative and quantitative ways. The key activities are described below. The objective of the State of Practice review was to identify and document ATM deployments in the United States, as well as available guidance from the Manual of Uniform Traffic Control Devices (MUTCD). The review collected descriptions and photos of permanent and temporary ATM systems in 27 states, including deployments of multipurpose overhead lane use control signs , dynamic lane control and dynamic lane reversal, dynamic shoulder lanes, dynamic speed limits, dynamic junction control, dynamic merge control, and dynamic queue warning. ATM applications in work zones were also documented, as well as the types of static signage placed in advance of ATM deployments. Additionally, international ATM deployments and existing in-vehicle ATM messaging approaches are also documented. The State of Practice review provided important context to the broader project by highlighting the variations in ATM deployments, and thus the need for additional research and guidance for presenting dynamic ATM information to drivers. Along with the State of Practice review, a literature review was conducted to synthesize recent and relevant findings. A literature search was conducted using both broad search and focused search processes. A total of 404 articles were searched, and 26 of those articles went through a structured, in-depth review. The literature review identified a number of data sources that provided general design guidance for ATM messages. However, practical answers to key research questions 1-4 were not provided by the existing literature. The output of the literature review was used to identify key research gaps and develop research questions for the Phase 2 activities. The findings from the literature review and State of Practice provided inputs to structured research gap analysis that was conducted to refine and prioritize the research needs that could be addressed in the project. The literature review and State of Practice generated 13 research gaps focusing on how the evolving alternative information channels could impact the role of DOT infrastructure and messaging practices. After identifying the 13 research gaps, three subject matter experts individually rated each research gap along five-point scales using three criteria: (a) relevance, (b) usefulness, and (c) expected cost. After all ratings were finalized, overall priority scores were calculated for each research gap. Following the initial evaluation of the 13 research gaps, the project team conducted further discussions and received input on the gaps from a State DOT stakeholder group and the NCHRP project panel. Two research gaps were excluded because they were not highly relevant or feasible. To address the remaining 11 research gaps, two driving simulator studies and a separate stakeholder engagement study were conducted. The first driving simulator study investigated the effects of the availability of the ATM information on driver behavior and distraction. The study focused on a dynamic lane signaling application and compared drivers’ behavior under two levels of information availability (“always-on” mode, which displayed the lane closure information always vs. “just-in-time” mode, which displayed the information only when a vehicle was near a corresponding overhead gantry) for smartphone ATM applications. Drivers were more likely to follow the lane closure information when they received the information from both the smartphone and overhead gantry at the same time, compared to when they received the information only from the overhead gantries. In addition, when the ATM information was available from both the smartphone and overhead gantry, there were no significant differences between the two levels of information availability on drivers’ compliance of lane closure information. However, the post-experiment survey showed that 70% of the participants preferred the “always-on” mode over the “just-in-time” mode. An analysis of driver glances showed that total glance time and average glance duration to the smartphone in the study were below the Alliance of Automobile Manufacturers (AAM)’s distraction criterion for human-machine interface interaction. The average glance duration to the smartphone was around 0.5 seconds. The results indicated that disseminating the ATM information via the smartphone along with the navigation information did not cause additional visual distraction. Given the sample size (n = 44) and limitations of the driving simulator study, differences observed in the study were too small to have practical significance. However, the study simulated situations in which ATM information can be disseminated from alternative ATM media and/or traditional ATM media, and it provided useful information about how to effectively use alternative media for ATM message dissemination in conjunction with infrastructure-based media. The output of the study was used to develop design guidelines and recommendations. The second driving simulator study investigated the effects of information modality (visual symbols vs. visual symbols and auditory messages) and information type (descriptive auditory messages vs. prescriptive auditory warning) of in-vehicle ATM displays on driver behavior and distraction. The research questions were examined in the context of a dynamic speed limit application. Drivers were more likely to drive 5 mph above the speed limit when they received the dynamic speed limit information from only the smartphone compared the other conditions. The results showed that when the smartphone was the sole source of ATM information, drivers were more likely to drive above the speed limit. Although there were no significant differences between modality conditions or information type conditions, the post-experiment survey showed that 60% of the participants preferred both a combined auditory-visual modality and descriptive information for the smartphone ATM application. Similar to the first driving simulator study, an analysis of driver glances showed that total glance time and average glance duration to the smartphone in the study were below the AAM’s distraction criterion for human-mahine interface interaction in all conditions. However, providing visual speed limit information on the smartphone increased glances towards the application relative to when speed limit information was only available on the gantry (i.e., when the smartphone only presented navigation information). This effect dimished when the the speed limit information on the smartphone was also presented as an auditory message in addition to the visual message. The results suggest that the addition of auditory messages enabled drivers to maintain the same focus on the driving task as they did when ATM information was only displayed on the infrastructure. The stakeholder engagement study was conducted to identify current and best practices used by agencies to effectively deploy and quantitatively evaluate the potential and realized benefits of various ATM strategies. Gaps within currently available guidelines and requirements were identified and guidance to support a transition to innovative, non-traditional media for presenting dynamic information was also investigated. This study relied on email communications, targeted web-based surveys and virtual telephone interviews, and a focus group to gather information from 13 transportation agencies about a variety of permanent and temporary ATM deployments. This study showed that 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 varied 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 in work zones noted challenges with evaluation due to the short duration and different conditions for each location. Many respondents struggled with defining how their agency balances driver needs versus safety, mobility, and costs for ATM deployments, with some interviewees saying they were not sure that their agencies fully understood “driver needs”. Survey responses showed varying responses, 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. Regarding available ATM resources and gaps, peer exchanges and interactions with other agencies that have deployed ATM strategies were cited most frequently as the primary, and often best, resource. Respondents also noted a variety of Federal Highway Administration (FHWA) resources and the MUTCD. Respondents identified resource gaps in many topic areas, particularly message display, sign placement, and software and algorithm development for automated operations. In-vehicle messaging resources were not identified as a gap, perhaps in part due to agency liability concerns, limited testing and deployment, or reliance on the private sector or other non-agency partners to develop and facilitate the provision of in-vehicle messages. 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 did not address each research gap completely. Based on the findings, initial design guidelines and recommendations were generated. This information was presented as two separate “guidelines” that provided high-level design information target at ATM message developers. Each guideline included additional discussion and design issues developed based on the best-available information from the literature review and empirical activities. Guideline 1 stated that: Alternative ATM media must be coordinated with the primary information provided by infrastructure-based ATM media. The following attributes support good use of traditional and alternative ATM media. • Alternative media should supplement, not replace infrastructure-based ATM media • Ensure that alternative ATM media information type and timing are consistent with the ones used in the infrastructure-based ATM messages • Use alternative ATM media to present persistent information continuously • The presentation timing of alternative ATM media should complement or match the time-course of infrastructure-based ATM messages • Coordinate onset timing of alternative ATM media to the legibility distance of infrastructure-based ATM media Guideline 2 stated that : When used to supplement traditional ATM media, an alternative ATM medium’s message modality, message type, and location should have characteristics that promote driver information retention and understanding, without causing distraction. • Use auditory-visual (AV) messages for alternative ATM media rather than visual-only messages o When providing auditory messages for dynamic speed limits, use descriptive messages and avoid prescriptive messages • Avoid using alternative ATM media as sole sources of ATM information • Different combinations of modalities suit different levels of complexity; match message modality to message complexity • In-vehicle displays should be in a location central to the driving task. Special accommodations should be made for smartphone displays Overall, ATM information dissemination is still an emerging topic that requires further research to establish best practices. Nevertheless, this project made significant strides toward framing the research gaps and addressing some of those information needs.
Refining distraction potential testing guidelines by considering differences in glancing behavior
Driver distraction is a recognized cause of traffic accidents. Although the well-known guidelines for measuring distraction of secondary in-car tasks were published by the United States National Highway Traffic Safety Administration (NHTSA) in 2013, studies have raised concerns on the accuracy of the method defined in the guidelines, namely criticizing them for basing the diversity of the driver sample on driver age, and for inconsistent between-group results. In fact, it was recently discovered that the NHTSA driving simulator test is susceptible to rather fortuitous results when the participant sample is randomized. This suggests that the results of said test are highly dependent on the selected participants, rather than on the phenomenon being studied, for example, the effects of touch screen size on driver distraction. As an attempt to refine the current guidelines, we set out to study whether a previously proposed new testing method is as susceptible to the effects of participant randomization as the NHTSA method. This new testing method differs from the NHTSA method by two major accounts. First, the new method considers occlusion distance (i.e., how far a driver can drive with their vision covered) rather than age, and second, the new method considers driving in a more complex, and arguably, a more realistic environment than proposed in the NHTSA guidelines. Our results imply that the new method is less susceptible to sample randomization, and that occlusion distance appears a more robust criterion for driver sampling than merely driver age. Our results are applicable in further developing driver distraction guidelines and provide empirical evidence on the effect of individual differences in drivers’ glancing behavior.
