Paper the Resilience of ITS: Variable Message Signs Contribution to Road Network Resilience under Incident and High Congestion Conditions: A State of the Art Review

Any failure or disruption in traffic flow can propagate through the road network. However, the server of such disruption and its consequences depends on the robustness and resiliency of transportation systems. In this context, traffic management (TM) measures will help the traffic stream to prevent the occurrence of such conditions or recover faster after experiencing the disruption. The main objective of this paper was to elaborate the contribution of TM measures to the resiliency of transportation systems, as well as, their vulnerability against external threats. Furthermore, a concept design for variable message signs (VMS) is developed and evaluated in terms of contribution to the resiliency of road networks. As well, new vulnerabilities associated with the implementation of VMS are investigated. The result of this study pointed out that ramp-metering, variable message signs, variable speed limits, and autonomous vehicles are valuable tools to mitigate the severity of traffic disruptions. VMS is one of the most effective approaches that enhance traffic resiliency by reducing traffic inflow to congested areas. However, these measures have opened new vulnerabilities to threats, especially cyber-attacks. Several cases of VMS hacks have occurred in the world and provided false messages to road users. It gets even worse with using an integrated wireless communication interface. Therefore, it is necessary to consider the security of such systems in advance, before practical application.

The verbiage in variable message signs and traffic diversion during crash incidents

Purpose–WIth limited research on the effects of variable message sign(VMS)message content and verbiage on revealed driver behavior,this study aims to investigate how different verbiage of crash-related messages are related to the diversion rate.Design/methodology/approach–Using ordered logit models,the associations of message verbiage with diversion rates during crash incidents were assessed using five years of VMS message history within a section of I-15 in the state of Utah.Findings–A significant impact of message verbiage on the diversion rate was observed.Based on the analysis results,the crash message verbiage with the highest diversion was found to be miles to crash 1“prepare to stop,”followed by crash location 1 delay information,miles to crash 1“use caution”1 lane of the crash,etc.In addition,the diversion rate was found to be correlated to some roadway characteristics(e.g.occupancy in mainline,weather condition and light condition)along with the temporal variations.Research limitations/implications–These findings could be used by transportation agencies(e.g.state department of transportation[DOTs])to make informed decisions about choosing the message verbiage during future crash incidents.This study also revealed that higher diversion rates are associated with a shorter distance between the crash location and VMS device location,recommending increasing the number of VMS devices,particularly in crash-prone areas.

Review of the Effectiveness of Vehicle Activated Signs

This paper reviews the effectiveness of vehicle activated signs. Vehicle activated signs are being reportedly used in recent years to display dynamic information to road users on an individual basis in order to give a warning or inform about a specific event. Vehicle activated signs are triggered individually by vehicles when a certain criteria is met. An example of such criteria is to trigger a speed limit sign when the driver exceeds a pre-set threshold speed. The preset threshold is usually set to a constant value which is often equal, or relative, to the speed limit on a particular road segment. This review examines in detail the basis for the configuration of the existing sign types in previous studies and explores the relation between the configuration of the sign and their impact on driver behavior and sign efficiency. Most of previous studies show that these signs have significant impact on driver behavior, traffic safety and traffic efficincy. In most cases the signs deployed have yielded reductions in mean speeds, in speed variation and in longer head-ways. However most experiments reported within the area were performed with the signs set to a certain static configuration within applicable conditions. Since some of the aforementioned factors are dynamic in nature, it is felt that the configurations of these signs were thus not carefully considered by previous researchers and there is no clear statement in the previous studies describing the relationship between the trigger value and its consequences under different conditions. Bearing in mind that different designs of vehicle activated signs can give a different impact under certain conditions of road, traffic and weather conditions the current work suggests that variable speed thresholds should be considered instead.

Leave the expressway or not? Impact of dynamic information

This study investigates drivers＇ diversion decision behavior under expressway variable message signs that provide travel time of both an expressway route and a local street route. Both a conventional cross-sectional logit model and a mixed logit model are developed to model drivers＇ response to travel time information. It is based on the data collected from a stated preference survey in Shanghai, China. The mixed logit model captures the heterogeneity in the value of ＂travel time＂ and ＂number of traffic lights＂ and accounts for correlations among repeated choices of the same respondent. Results show that travel time saving and driving experience serve as positive factors, while the number of traffic lights on the arterial road, expressway use frequency, being a middle-aged driver, and being a driver of an employer-provided car serve as negative factors in diversion. The mixed logit model obviously outperforms the cross-sectional model in dealing with repeated choices and capturing heterogeneity regarding the goodness-of-fit criterion. The significance of standard deviations of random coefficients for travel time and number of traffic lights evidences the existence of hetero- geneity in the driver population. The findings of this study have implications for future efforts in driver behaviormodeling and advanced traveler information system assessment.