Dynamic Message Signs Research Articles

Theory of safety surrogates using vehicle trajectories in macroscopic and microscopic settings: Application to dynamic message signs controlled traffic at work zones

This paper presents a new mathematical framework for obtaining quantitative safety measure using macroscopic as well as microscopic traffic data. The safety surrogate obtained from the macroscopic data is in terms of analysis performed on vehicle trajectories obtained from the macroscopic data. This method of obtaining safety measure can be used for many different types of applications. The safety surrogate for the traffic dynamics are developed in terms of a new concept of Negative Speed Differentials (NSD) that involve a convolution of vehicle speed function obtained from vehicle trajectories and then performing the integration of the square of the output for its negative values. The framework is applicable to microscopic traffic dynamics as well where we can use car following models for microscopic dynamics or the LWR model for macroscopic dynamics. This paper then presents the use of this new safety surrogate on the development of a feedback control law for controlling traffic in work zones using Dynamic Message Signs. A hybrid dynamics model is used to represent the switching dynamics due to changing DMS messages. A feedback control design for choosing those messages is presented as well as a simple simulation example to show its application.

Fatigue analysis of sign-support structures during transportation under road-induced excitations

Dynamic Message Signs (DMSs) are increasingly used in highways as an effective means to communicate time-sensitive information with motorists. To ensure the long-term performance of DMSs, it is critical to ensure that the truss structures that hold them can resist not only extreme loading events, but also fatigue induced by service loads. The existing studies, however, are primarily focused on the loads that DMS-support structures experience during their service life and neglect the potential contribution of stresses induced during the transportation of them from the fabrication site to the location of installation. As a result, the potential damage that this important category of structures may sustain during transportation had remained largely unknown. To investigate this aspect, a comprehensive field test and numerical study were conducted. For field investigation, one span of a four-chord, overhead sign-support structure was instrumented to perform a short-term structural health monitoring. In addition, detailed finite element simulations were conducted to obtain an in-depth understanding of the potential modes of damage under the excitations induced by the road profile. The outcome of this study is expected to contribute to evaluating the extent of fatigue and structural vulnerability of DMS-support structures during transportation.

Developing an algorithm to assess the rear-end collision risk under fog conditions using real-time data

This study aims to propose a new algorithm to evaluate the rear-end collision risk under fog conditions considering reduced visibility. The proposed algorithm compares the safe stopping distance of the leading and following vehicles. According to the relationship between clearance distance between the two consecutive vehicles and visibility distance, the car-following maneuver is divided into different situations and the algorithms to calculate the safe stopping distances are suggested correspondingly. The visibility distance is collected by a new visibility detection system with adaptive learning modules and the clearance distance is obtained from a vehicle-based detector. By comparing the safe stopping distances of the following and leading vehicles, the potential rear-end collision can be identified. Subsequently, statistical tests are conducted to analyze rear-end collision risk and compare the different impact of reduced visibility on the collision risk for different vehicle types and lanes. Furthermore, random parameters logistic and negative binomial models are estimated by using individual vehicle data and aggregated traffic flow data, respectively, in order to explore the relationship between the potential rear-end crash and the reduced visibility together with other traffic parameters. The results suggest that the proposed algorithm works well in evaluating rear-end collision risk under fog conditions. It is found that reduced visibility has significant impact on the rear-end collision risk and the impact vary by the different vehicle types and by lane. Further, it is concluded that the driving maneuver of the leading and following vehicles can affect the rear-end collision risk. It is expected that the proposed algorithm can be implemented in a Traffic Management context to improve road safety under fog conditions. Specifically, it is suggested to implement the proposed algorithms in real-time and integrate it with ITS technologies such as Variable Speed Limit (VSL) and Dynamic Message Signs (DMS) to enhance traffic safety when the visibility declines. This car following algorithm could also be extended to adapt for the advent of Connected Vehicles in Fog conditions.

Effects of real-time warning systems on driving under fog conditions using an empirically supported speed choice modeling framework

Fog warning systems can convey warning messages to drivers and help to reduce crashes that may occur due to the sudden occurrence of low visibility conditions. This study aims to assess the effectiveness of real-time fog warning systems by quantifying and characterizing drivers’ speed adjustments under different roadway types, traffic conditions, and fog levels. In order to explore how a driver perceives the fog warning systems (i.e., beacon and dynamic message signs (DMS)) when approaching a fog area, this paper divides the roads into three zones (i.e., clear zone, transition zone, fog zone) according to visibility levels and suggests a hierarchical assessment concept to explore the driver’s speed adjustment maneuvers. For the three different zones, different indexes are computed corresponding to drivers’ speed adjustments. Two linear regression models with random effects and one hurdle beta regression model are estimated for the indexes. In addition, the three models were modified by allowing the parameters to vary across the participants to account for the unobserved heterogeneity. To validate the proposed analysis framework, an empirical driving simulator study was conducted based on two real-world roads in a fog prone area in Florida. The results revealed that the proposed modeling framework is able to reflect drivers’ speed adjustment in risk perception and acceleration/deceleration maneuvering when receiving real-time warning massages. The results suggested that installing a beacon could be beneficial to speed reduction before entering the fog area. Meanwhile, DMS may affect drivers’ brake reaction at the beginning section of reduced visibility. However, no effects of warning systems for drivers’ final speed choice in the fog can be observed. It is suggested that proper warning systems should be considered for different conditions since they have different effects. It is expected that more efficient technology can be developed to enhance traffic safety under fog conditions with a better understanding of the drivers’ speed adjustments revealed in this study.

Work zone sign design for increased driver compliance and worker safety

Many studies have investigated the effect of dynamic message signs (DMS) on drivers’ speed reduction and compliance in work zones, yet only a few studies have examined the design of sign content of DMS. The purpose of this study was to develop design standards for DMS to improve driver compliance and worker safety. This study investigated the impact of sign content, frame refresh rate, and sign placement on driver speed reduction, compliance, and eye movements. A total of 44 participants were recruited for this study. Each participant completed 12 simulated driving tasks in a high-fidelity driving simulator. A small-scale field study was also conducted to test the effect of DMS on vehicle speed in a highway work zone. Results showed sign content and placement had no impact on speed reduction and compliance. However, sign frame refresh rate was found to have a significant effect on drivers’ initial speed and speed reduction. Participants had longer fixation duration on DMS when worker presence was mentioned in the sign content. Results of the field study suggested that the DMS is most effective at night.

Evaluation of Real-Time Transit Information Systems: An information demand and supply approach

Abstract This study assesses current needs in the implementation of Real-Time Transit Information Systems. Web surveys are used to better understand information supply and demand, defined as the attitudes and experiences with real-time information of transit passengers and agencies, respectively. The most valued types of information demanded were found to be related to vehicle location while the least valued information relates to vehicle characteristics, like seating availability. Smartphone applications were found to be the preferred medium for receiving information followed by Internet/websites and dynamic message signs. The surveys also revealed that demographic and socioeconomic status influence preferences for real-time information. The information supply survey found that approximately 70 percent of surveyed agencies currently offer real-time information. The largest constraint to providing or improving Real-Time Transit Information Systems (RTTISs) was found to be funding, followed by staffing needs. A comparison between the survey results found that the information currently being provided by transit agencies is mostly in line with the information most valued by transit passengers. The few differences that exist are generally because agencies do not provide information on the media preferred most by passengers. To address these differences, several suggestions are made to improve the implementation of real-time information. This information can be used to better develop and prioritize investment in real-time information systems.

Decision-Making Framework to Allocate Real-Time Passenger Information Signs at Bus Stops: Model Application in Athens, Greece

The use of intelligent transport systems for the provision of real-time passenger information is an important incentive in efforts to strengthen the role of public transport and improve livability in large cities. Electronic signs installed at bus stops to disseminate information on bus arrivals are an important component of these systems with a significant capital cost. Nonetheless, to the best of the authors’ knowledge, there is no systematic approach for the selection of location sites for deployment of dynamic message signs (DMS). Public transport authorities often follow ad hoc procedures that are based on various location criteria—namely, passenger boardings, availability of power, and number of routes served at bus stops—to derive a set of candidate location sites. This was the case with the methodology implemented by the Athens Urban Transport Organization in Athens, Greece. With data from Athens, this paper proposes a modeling framework for the decision-making process regarding DMS locations in bus networks. The framework is formulated as a linear programming model, and the results show that the proposed model constitutes a systematic and transferable approach to tackle the problem at hand.

Safety Impacts of Queue Warning in a Connected Vehicle Environment

Queue warning systems (QWSs) have been implemented to increase traffic safety by informing drivers about queued traffic ahead so that they can react in a timely manner to the queue. Existing QWSs rely on fixed traffic sensors to detect the back of a queue. It is expected that if the transmitted messages from connected vehicles (CVs) are used for this purpose, detection can be faster and more accurate. In addition, with CVs, delivery of the messages can be done with onboard units instead of dynamic message signs and provide more flexibility on how far upstream of the queue the messages are delivered. This study investigates the accuracy and benefits of the QWS on the basis of CV data. The study evaluated the safety benefits of the QWS under different market penetrations of CVs in future years. Surrogate safety measures were estimated with simulation modeling combined with the surrogate safety assessment model tool. Results from this study indicate that a relatively low market penetration—about 3% to 6%—for the congested freeway examined in this study was sufficient for an accurate and reliable estimation of the queue length. Even at 3% market penetration, the CV-based estimation of back-of-queue identification was significantly more accurate than that based on detector measurements. The results also found that CV data allowed faster detection of the bottleneck and queue formation. Further, the QWS improved the safety conditions of the network by reducing the number of rear-end conflicts. Safety effects become significant when the compliance percentage with the queue warning messages is more than 15%.

Virtual dynamic message signs: a future mode for basic public traveller information

The most common mode for en-route public traveller information is dynamic message signs (DMSs). Despite their effectiveness, they are costly and limited in the amount of information they can deliver. The wide availability of smart mobile devices and communication technologies offers possibilities to provide traveller information not only through in-vehicle devices without incurring huge infrastructure costs, but also in a more flexible manner to selected individuals and at specific locations without geographical constraints. This study proposed the concept of virtual DMSs (VDMSs) to improve public traveller information provision. In order to evaluate the effectiveness of such systems, the study first prototyped a smartphone-based VDMS application and conducted a focused group user experience survey, which revealed a positive attitude towards VDMS in terms of both usefulness and satisfaction. Second, a driving simulator study was conducted to analyse two other critical aspects of VDMS, message comprehension and driver distraction. Results revealed that VDMS generally performs better than DMS across different amounts of information provision and under different driving conditions regardless of driver age. It is recommended that transportation agencies give full consideration to VDMS as a future strategy for delivering public traffic information in a connected vehicle environment.

ASSESSING AND MITIGATING THE IMPACTS OF DYNAMIC MESSAGE SIGNS ON HIGHWAY TRAFFIC

As a critical component in Intelligent Transportation Systems (ITS) of modern traffic management, dynamic message signs (DMS) are widely used in many countries as an effective means to provide motorists with up-to-date information regarding accidents, congestion, road conditions and travel time, etc. However, it was observed in traffic data that motorists tended to slow down when approaching active DMSs and speed up after passing these signs. The speed variations could pose safety hazards to other motorists on highways. To gain insights into this issue and understand associated causes and risks, a human factors study was conducted to help ease the speed variation when approaching DMSs. The effect of DMS messages on traffic approaching and passing the signs were assessed by analyzing highway traffic data near DMSs. A questionnaire survey was conducted to identify associated causes and risks. Participants were further surveyed about their preferences on DMS characteristics such as message category, message type, number of frames, message details, and the use of graphics. Individual drivers' responses to various DMS designs were evaluated through a simulation test. This study has provided updated knowledge regarding the effects of DMSs on highway traffic and has identified measures to improve the design and display of DMS messages to help ease the speed variation of approaching traffic.

Application of Inductive Loop Detectors and Dynamic Message Signs in Addressing Wrong-Way Driving Issues: A Technical Specification

Application of Inductive Loop Detectors and Dynamic Message Signs in Addressing Wrong-Way Driving Issues: A Technical Specification

Should Legacy Highway Advisory Radio and Citizens’ Band Radio Advisory Systems Be Continued?: Analysis of Traveler Usage and Satisfaction Regarding These Systems

Advanced traveler information systems (ATIS) are important to provide travelers with accurate, up-to-date travel information. With the advent of new ATIS technologies, such as smartphone applications, roadway agencies need to understand how travelers use existing ATIS technologies, such as the legacy Highway Advisory Radio (HAR). The University of Central Florida implemented three traveler surveys and one truck driver survey to obtain the opinions of Florida roadway users regarding HAR, the Citizens’ Band Radio Advisory System (CBRAS), and other traffic information sources. Travelers typically preferred dynamic message signs (32%), smartphone applications (23%), and vehicle navigation devices (21%) for general traffic information. Some 57% of travelers were aware of HAR, and 42% of these travelers had used HAR, with 84% of users expressing satisfaction with HAR. Additionally, 87% of travelers said that they would use HAR during emergencies, such as hurricanes. A tree model targeting user satisfaction was developed; the model showed that HAR users who thought HAR should be continued, or who would use HAR in emergencies, as well as more frequent HAR users, were more likely to be satisfied. Only 12% of surveyed truck drivers had ever used CBRAS, but these users tended to utilize CBRAS frequently, and 92% indicated satisfaction with CBRAS. Truck drivers preferred vehicle navigation devices (28%) and smartphone applications (22%) to receive traffic information. Even though these surveys indicate that new technologies are more popular than HAR and CBRAS, these older systems satisfy users and should be kept for redundancy; cellular communications may fail during emergencies.

Assessing spatial and temporal effects due to a crash on a freeway through traffic simulation

The focus of this paper is to simulate, evaluate and assess spatial and temporal effects in travel time variation and upstream distance or length of upstream links affected due to a crash. Traffic simulations were conducted for different conditions in VISSIM 5.30™ to obtain travel times at various points upstream of the crash location, over time, along a freeway corridor. Travel time variation between fatal crash condition and no crash condition (baseline condition) and between injury crash condition and no crash condition (baseline condition) were computed and compared to evaluate the effect of a crash on a freeway. Results obtained showed that fatal crash on freeways has an effect under low, moderate, and high traffic volume conditions, whereas injury crash has an effect only under moderate and high traffic volume conditions. The travel time variation and upstream distance affected due to a fatal crash on the right-most lane was generally higher than fatal crash on the left-most lane. The trends remained fairly consistent irrespective of the lane on which an injury crash occurred. The upstream distance affected due to a fatal crash varied from 1.5 miles to ∼7.5 miles based on traffic volume and lane on which the fatal crash occurred. It varied from ∼0.5 miles to 7 miles due to an injury crash and traffic condition. Queue may start dissipating at least 15min after blocked lanes are re-opened for normal traffic flow depending on the type of crash, traffic volume and lane in which the crash occurred. The results and findings from this research can be applied to emulate dynamic message signs over time and space so as to alert the motorists about the length and duration of congestion depending on the severity of crash and lane on which the crash occurred.

Driving simulator‐based study of compliance behaviour with dynamic message sign route guidance

This study uses a hybrid approach that incorporates a driving simulator (DS) in conjunction with a stated preference (SP) survey to analyse driver response behaviour under real-time route guidance through dynamic message signs (DMSs). It seeks to better understand factors affecting the route choice decisions by bridging some of the key gaps that limit the applicability of SP approaches. A 400 km2 network southwest of the Baltimore metro area is used for the DS-based analysis with over 100 participants. The results illustrate that past exposure to DMS, travel time savings, DMS information reliability and learning from past experience are important determinants of driver response behaviour in the real world. Moreover, in addition to travel time, inertia and anchoring effects can significantly influence choice decisions. This study also illustrates that the decisions revealed in the simulator experiments at the individual level can diverge significantly from those stated in the SP questionnaire, highlighting the need to go beyond stated intent to analyse the effectiveness of information-based guidance strategies.

Comparison of In-Vehicle Auditory Public Traffic Information With Roadside Dynamic Message Signs

Dynamic message signs (DMS) have been widely used by transportation agencies to disseminate traffic information (referred to in this article as “public traffic information”) for decades. Unfortunately, their effectiveness is limited, based on the following reasons: they are costly, can only present a limited amount of information, and typically only display information in one language. The wide availability of smart devices and the development of connected vehicles offer the possibility to create “virtual” DMS (VDMS), utilizing geofencing and audible messages to convey public traffic information. This research compares the ability of VDMS to convey public traffic information with existing DMS. A mixed repeated-measure experiment using a driving simulator was designed that examined the impacts of driver age, information transmission mode, amount of information, and driving complexity on message comprehension. Forty-two participants were recruited and each of them was tested under different combinations of the three within-subject factors. Participant performance was measured in terms of message comprehension, distraction, and self-reported overall difficulty level in receiving messages. Results revealed that VDMS generally performs better than DMS as information content increases and driving condition complexity increases, regardless of driver age. VDMS increased message comprehension by 16% under relatively complex driving conditions, reduced driver reaction time to unexpected stimuli (as measured with a reduced time-to-brake of 0.39 s), and made the same messages easier to process and retain for drivers than DMS. Based on these results, it is recommended that transportation agencies give careful consideration to VDMS as a future strategy for delivering public traffic information in a connected vehicle environment.

Impact of Dynamic Message Signs on Speeds Observed on a Rural Interstate

Dynamic message signs (DMSs) are a component of intelligent transportation systems (ITSs) used to convey real-time travel information to motorists, enabling them to make better decisions in response to real-time roadway conditions such as congestion, crashes, and adverse weather. The purpose of this paper is to analyze the existing DMS system implemented by the Wyoming Department of Transportation (WYDOT) along a rural segment of Interstate 80 in southeastern Wyoming between the cities of Laramie and Cheyenne. The research uses speed, weather, and DMS message data collected from the winter season of 2009 to 2010 along the corridor to determine how driver speed behavior is affected by DMS signs. A linear regression model utilizing four different weather severity categories was estimated and the results indicate that the DMS message signs are effective at reducing drivers’ speeds along rural interstate corridors from 8 km/h to 32 km/h (5 mi/h to 20 mi/h) above the speed reductions that can be accounted for by weather conditions alone.

Thermal Analysis of Highway Overhead Support Structures

Dynamic message signs are increasingly used on freeways, expressways, and major arterials to manage traffic flow better by providing accurate and timely information to drivers. Overhead truss structures that allow for wide displays across multiple travel lanes are typically used to support those signs. Recently, cracks at welded toes in these structures have been identified in multiple states. The AASHTO standard specification defines the loads to be considered during design as wind load, dead load, live load, and ice load, and fatigue design for wind galloping, vortex shedding, natural wind gust, and truck-induced gust. Notably missing from this list is any consideration for thermal loads. Although the number of thermal cycles is relatively low, the temperature variations are relatively large. Should these large temperature ranges result in large stresses, the potential for fatigue failures to initiate, principally from thermal variations, exists. The objectives of this study were to investigate the influence of thermal- and wind-induced loads on bridge-type overhead truss support structures and to provide a resource aimed at improving current design specifications for thermal design. To provide a solid baseline for this work, field monitoring of several overhead trusses was conducted. The evaluation of the collected data was important for understanding the structural behavior and for the advancement of any future code provisions. In addition, finite element modeling was conducted to further study strain and stress magnitudes, which were compared with the field monitoring data. The fatigue life of the truss structures was also estimated on the basis of AASHTO specifications and the numerical modeling results.

Evaluation of Dynamic Message Signs on Rural Freeways: Case Study of a Full Freeway Closure

The evaluation of dynamic message signs (DMSs) has been challenging to undertake because of the difficulty of identifying the effects of DMSs from traffic patterns. The primary contribution of this study is the comprehensive evaluation of DMSs in a rural area during a full freeway closure by using field data, driver surveys, and simulation. A full freeway closure scenario offers an opportunity to identify the effects of DMSs, because there is a network-wide shift in traffic demand from the closed route to the alternate route(s). A unique data collection and analysis approach was used to capture regional traffic patterns, including the processing of all traffic movements from four full interchanges. A significant increase in traffic flow on the detour route and a corresponding decrease on the affected route were observed during the freeway closure. Simulation was used to isolate the benefits of DMSs from other traveler information modes such as newspaper, TV, and radio, and to explore the sensitivity of the network to different levels of driver compliance. Depending on the proportion of drivers who chose to divert based on DMSs, monetary benefits were estimated to range between US$2,394 and $65,643 for the three-day freeway closure. Driver surveys conducted during the freeway closure revealed that 57% of the drivers utilized DMS information and 41% of drivers relied solely on DMSs to obtain information related to the closure and the detour route.

After-Fracture Reserve Strength of Two Four-Chord Aluminum Sign Trusses

AbstractMany departments of transportation use four-chord aluminum tubular truss structures to support dynamic message signs (DMS). Inspections have often revealed that these structures contain cracks that likely occurred during or shortly after fabrication or were caused by fatigue while in service. Nearly all of these cracks are located at welded tube-to-tube connections, such as the diagonal-to-main chord fillet welded connections. Both weld toe cracks and surface-breaking root cracks have been observed. Destructive testing was conducted to evaluate the after-fracture reserve strength (AFRS) of 21.3-m-span and 16.8-m-span aluminum four-chord trusses. The dead weight of a DMS was simulated by attaching steel beams of the same weight eccentric to one exterior side of the truss near midspan. Wind load was simulated by hydraulic jacks and a whiffle-tree loading configuration. Simple steel frames were fabricated to mimic the sign truss end supports. Realistic boundary conditions, similar to the truss-to-end...

Traffic Management Effects of Variable Speed Limit System on a German Autobahn

An empirical study of the traffic flow effects of a variable speed limit (VSL) system on a three-lane German autobahn is presented. The study integrated loop detector data and VSL and driver information provided by overhead dynamic message signs along a 16.3-km section of Autobahn A99 near Munich, Germany. Unlike most VSL deployments, the data sources allowed for a with-and-without analysis to reflect traffic flow and driver behavior in the presence and in the absence of the VSL system. In addition to speed, the primary features of interest were the spatial–temporal extent of the queue (congestion), flow changes caused by identified bottlenecks, the distribution of flow across lanes, the percentage of trucks per lane, and the flow homogeneity between lanes. The analysis recorded bottleneck flow reductions that were balanced across all lanes with an active VSL system. With an inactive VSL system, the flow reductions were slightly lower and occurred primarily in the center and shoulder lanes; there was a small flow increase in the median lane. Further examination indicated that the gain in homogeneity and safety with the system in place was at the cost of capacity. Possible reasons that might explain the differences between the scenarios with and without the VSL system had their basis in the ban against passing by trucks, which was in effect when the driver information system was active.