Francois Dion

Vehicle-to-vehicle wireless communication protocols for enhancing highway traffic safety

This article presents an overview of highway cooperative collision avoidance (CCA), which is an emerging vehicular safety application using the IEEE- and ASTM-adopted Dedicated Short Range Communication (DSRC) standard. Along with a description of the DSRC architecture, we introduce the concept of CCA and its implementation requirements in the context of a vehicle-to-vehicle wireless network, primarily at the Medium Access Control (MAC) and the routing layer. An overview is then provided to establish that the MAC and routing protocols from traditional Mobile Ad Hoc networks arc not directly applicable for CCA and similar safety-critical applications. Specific constraints and future research directions are then identified for packet routing protocols used to support such applications in the DSRC environment. In order to further explain the interactions between CCA and its underlying networking protocols, we present an example of the safety performance of CCA using simulated vehicle crash experiments. The results from these experiments arc also used to demonstrate the need for network data prioritization for safety-critical applications such as CCA. Finally, the performance sensitivity of CCA to unreliable wireless channels is discussed based on the experimental results.

Cooperative vehicle collision avoidance using inter-vehicle packet forwarding

This paper proposes a broadcast based packet forwarding mechanism for intra-platoon cooperative collision avoidance (CCA) using dedicated short range communication (DSRC) links. The paper first motivates the needs for broadcast forwarding as opposed to unicast routing for transporting inter-vehicle data for safety-critical applications. Then it introduces an implicit acknowledgement mechanism for reducing the amount of broadcast traffic for enhanced packet delivery rate. We have developed a discrete event hybrid simulator InventSim, which is capable of jointly simulating DSRC based vehicular wireless networks, highway vehicle traffic with car following logic and various drivers reaction models, and ITS application interface to the wireless network. Performance of the proposed broadcast forwarding for a CCA system has been characterized using InventSim. Reported results demonstrate that with inter-vehicle spacing of nearly one second, the proposed mechanism is capable of saving up to 90% of vehicles in a platoon from chain crashes following emergency events at the front of the platoon. The system has been also evaluated for a wide range of parameters including vehicle spacing, drivers reaction time, and the amount of background non-CCA traffic

Estimating Path Travel-Time Reliability

The estimation of path or trip travel-time reliability is critical to any advanced traveler information system. The state-of-practice procedures for estimating path travel-time reliability assumes that travel times follow a normal distribution and requires a measure of trip travel-time variance. The study analyzes AVI data from San Antonio and demonstrates through goodness-of-fit tests that the assumption of normality is, from a theoretical standpoint, inconsistent with field travel-time observations and that a lognormal distribution is more representative of roadway travel times. However, visual inspection of the data demonstrates that the normality assumption may be sufficient from a practical standpoint given its computational simplicity. The paper then proposes five methods for the estimation of path travel-time variance from its component segment travel-time variances. The analysis demonstrates that computing the trip travel-time coefficient of variation as the conditional expectation over all realizations of roadway segments provides estimates within 13% of field observations for both uncongested and congested conditions

Virtual Testbed for Assessing Probe Vehicle Data in IntelliDrive Systems

This paper presents an effort to develop a virtual testbed for assessing probe vehicle data generation by IntelliDrive vehicles within a microscopic traffic-simulation environment. Simulation capabilities are implemented through the development of a portable plug-in module using the application programming interface of the Paramics microscopic traffic simulation. This module simulates the generation of snapshots by individual vehicles, the uploading of these snapshots to roadside units, and some probe vehicle data postprocessing. While some temporary simplifying assumptions are made, the simulation generally follows operational concepts described in the Society of Automotive Engineers (SAE) J2735 Surface Vehicle Standard. Application of the model is demonstrated by simulating IntelliDrive probe data collection over the U.S. Department of Transportation (USDOT)s Michigan Proof-of-Concept testbed. Simulation results show the sensitivity of probe data collection to communication range, market penetration, number of active roadside communication units (RSEs), interval between snapshots, and snapshot buffer size. Impacts on link travel time estimates are also presented. These results clearly demonstrate the utility of the simulator in conducting evaluations and sensitivity analyses for scenarios that would be difficult to execute in existing testbeds.

Dedicated Short-Range Wireless Communications for Intelligent Transportation System Applications: State of the Art

In efforts to reduce traffic accidents and improve the efficient utilization of existing transportation networks, increasing attention is being given to the use of wireless communications between vehicles and roadside equipment to develop new intelligent transportation system (ITS) applications that can help improve the safety of transportation networks and reduce urban congestion. Of particular interest for the development of such applications are the currently proposed dedicated short-range communication (DSRC) wireless standards. This paper aims to provide transportation researchers and engineers with an introduction to these standards. The paper presents the current mobile wireless communication applications and standards, the various DSRC standards that have been proposed, their potential use in ITS applications, their envisioned implementation benefits, and the remaining research needs.

Evaluation of Usability of IntelliDrive Probe Vehicle Data for Transportation Systems Performance Analysis

This paper assesses various issues associated with the use of IntelliDrive probe vehicle data generated according to existing protocols. These evaluations are conducted using a virtual IntelliDrive probe vehicle data generator implemented within the Paramics microscopic traffic simulation model. Issues investigated included the ability to monitor queue conditions, the potential for data-sampling bias, effects of privacy rules on collected data, the ability to track vehicles over short distances, the magnitude of data latency induced by the protocols, and the ability to use probe vehicle data to estimate link travel times. The evaluations indicate various improvement needs: (1) generating snapshots at fixed intervals rather than at speed-based intervals, (2) promoting the use of short snapshot intervals, (3) allowing vehicles to include the snapshots they generate while stopped, (4) enabling vehicles to generate link exit snapshots, (5) allowing vehicles to keep uploading new snapshots generated while within range of a roadside communication unit, and (6) revising privacy protocols to ensure that adequate short vehicle tracks can be obtained. The impacts of current privacy rules on the ability to track vehicles over short distances are also outlined.

Safety Assessment of Information Delay on Performance of Intelligent Vehicle Control System

Recently, increasing attention has been put on the use of automated vehicle control systems to reduce traffic crashes due to driver errors. Proposed systems rely on either onboard range sensors or vehicle-to-vehicle wireless communications to obtain pertinent information about surrounding vehicles and to determine appropriate acceleration or deceleration commands. Although numerous studies have used microscopic traffic simulation to study the effects that these systems might have on traffic flows, generally these studies did not consider all factors that may affect their operation. A particular element that has been ignored is delay in data acquisition. Using a microscopic traffic simulation model that was developed to simulate intelligent transportation system applications relying on the use of onboard vehicle sensors or wireless transmissions, this paper attempts to quantify the safety effects created by the use of delayed information in automated vehicle control systems. The study clearly indicates that information delay affects the operation of vehicle control systems, particularly when sensor or transmission delays result in the use of information older than a certain threshold, found in this case to be 0.5 s.

A generalized framework for integrated vehicle traffic and wireless network simulation

This paper presents a generalized framework for integrating a wireless network simulator and a vehicle traffic simulator for rapid prototyping and evaluation of Dedicated Short Range Communication (DSRC) based vehicular communication protocols and their applications in the context of Intelligent Transportation System (ITS). A novel method of inter-simulator time synchronization has been designed to simulate the interactions between vehicles and wireless networks at resolutions of up to few tens of milliseconds. This fine grain time synchronization enables the simulation of time-critical ITS safety applications requiring less than 100 ms timing resolutions. The architecture-driven approach that has been adopted further leads to a generalized integration that is agnostic of the specific internal syntaxes used by the individual communication network and vehicle simulators that are being integrated. As a feasibility demonstration, the framework is used to integrate Paramics, a vehicular traffic simulator, with ns-2, a communication network simulator. The resulting integrated simulator is then utilized to investigate the performance of wireless message propagation in the context of a freeway car collision avoidance application.

Chain Collision Accident: Causes and Avoidance Techniques

This chapter reports on the chain of collisions that occur in case of emergency deceleration in a platoon of vehicles driving in a convoy. Chain Collision Avoidance applications are a new emerging means of reducing the number of chain accidents on the road by providing cars with collaborative communication capabilities, thus allowing them to react against the real risk of accident which may occur in different traffic circumstances. This chapter evaluates the Chain Collision Avoidance application under a wide range of parameters (time headway, reaction time, and recommendation speed) and measures the impact of each parameter on the number of collisions under different market penetration rates. In this chapter, an analytical model combined with extensive simulations is developed to investigate the impacts of low market penetration rate on the number of collisions.