Sebastien Demmel

Multi-Hypotheses Tracking using the Dempster-Shafer Theory, application to ambiguous road context

We develop a new method to solve ambiguities in tracks-target association in vehicular environments.Previous work with the Dempster-Shafer theory is improved by incorporating conflictual data in a beneficial way.Two Multi-Hypotheses Tracking methods are examined with their pro- and cons.Ambiguity removal is demonstrated with two examples: pedestrians crossing in front of a vehicle-mounted laserscanner, and an overtaking manoeuvre. This paper presents a Multi-Hypotheses Tracking (MHT) approach that allows solving ambiguities that arise with previous methods of associating targets and tracks within a highly volatile vehicular environment. The previous approach based on the Dempster-Shafer Theory assumes that associations between tracks and targets are unique; this was shown to allow the formation of ghost tracks when there was too much ambiguity or conflict for the system to take a meaningful decision. The MHT algorithm described in this paper removes this uniqueness condition, allowing the system to include ambiguity and even to prevent making any decision if available data are poor. We provide a general introduction to the Dempster-Shafer Theory and present the previously used approach. Then, we explain our MHT mechanism and provide evidence of its increased performance in reducing the amount of ghost tracks and false positive processed by the tracking system.

Comparing cooperative and non-cooperative crash risk-assessment

Cooperative Systems provide, through the multiplication of information sources over the road, a lot of potential to improve the assessment of the road risk describing a particular driving situation. In this paper, we compare the performance of a cooperative risk assessment approach against a non-cooperative approach; we used an advanced simulation framework, allowing for accurate and detailed, close-to-reality simulations. Risk is estimated, in both cases, with combinations of indicators based on the TTC. For the noncooperative approach, vehicles are equipped only with an AAC-like forward-facing ranging sensor. On the other hand, for the cooperative approach, vehicles share information through 802.11p IVC and create an augmented map representing their environment; risk indicators are then extracted from this map. Our system shows that the cooperative risk assessment provides a systematic increase of forward warning to most of the vehicles involved in a freeway emergency braking scenario, compared to a non-cooperative system.

An IEEE 802.11p empirical performance model for Cooperative Systems applications

IEEE 802.11p is the new standard for Inter-Vehicular Communications (IVC) using the 5.9 GHz frequency band, as part of the DSRC framework; it will enable applications based on Cooperative Systems. Simulation is widely used to estimate or verify the potential benefits of such cooperative applications, notably in terms of safety for the drivers. We have developed a performance model for 802.11p that can be used by simulations of cooperative applications (e.g. collision avoidance) without requiring intricate models of the whole IVC stack. Instead, it provide a a straightforward yet realistic modelisation of IVC performance. Our model uses data from extensive field trials to infer the correlation between speed, distance and performance metrics such as maximum range, latency and frame loss. Then, we improve this model to limit the number of profiles that have to be generated when there are more than a few couples of emitter-receptor in a given location. Our model generates realistic performance for rural or suburban environments among small groups of IVC-equipped vehicles and road side units.

Collision warning dissemination in vehicles strings: An empirical measurement

Inter-Vehicular Communications (IVC) are considered a promising technological approach for enhancing transportation safety and improving highway efficiency. Previous theoretical work has demonstrated the benefits of IVC in vehicles strings. Simulations of partially IVC-equipped vehicles strings showed that only a small equipment ratio is sufficient to drastically reduce the number of head on collisions. However, these results are based on the assumptions that IVC exhibit lossless and instantaneous messages transmission. This paper presents the research design of an empirical measurement of a vehicles string, with the goal of highlighting the constraints introduced by the actual characteristics of communication devices. A warning message diffusion system based on IEEE 802.11 wireless technology was developed for an emergency breaking scenario. Preliminary results are presented as well, showing the latencies introduced by using 802.11a and discussing early findings and experimental limitations

IEEE 802.11p Empirical Performance Model from Evaluations on Test Tracks

IEEE 802.11p is the new standard for intervehicular communications (IVC) using the 5.9 GHz frequency band; it is planned to be widely deployed to enable cooperative systems. 802.11p uses and performance have been studied theoretically and in simulations over the past years. Unfortunately, many of these results have not been confirmed by on-tracks experimentation. In this paper, we describe field trials of 802.11p technology with our test vehicles; metrics such as maximum range, latency and frame loss are examined. Then, we propose a detailed modelisation of 802.11p that can be used to accurately simulate its performance within Cooperative Systems (CS) applications.

860 Safe following distance? –driver perceptions to help reduce rear end road crashes in Australia

Background To reduce road trauma we must better understand the factors contributing to crashes. In Queensland, Australia, rear end crashes are the 3rd leading crash type, with mild to serious injuries a likely outcome and whiplash a common injury occurrence. Road design, traffic congestion, and weather/road conditions have been implicated in rear end crashes. Human factors also play a key role, with the act of ‘following too closely’ being a major issue. Queensland legislation requires motorists to maintain a safe following distance between their vehicle and the one in front, although no specific information about this distance is prescribed by law for cars. Methods To better understand perceptions of safe following distance, 495 licensed Queensland drivers (42% male; mean age 46.2 yrs; range 16–81 yrs) completed an online questionnaire. Results Overall, there was wide variation in descriptions of safe following distance including time between vehicles (2 seconds = 21%; 3 seconds = 11%), distance between vehicles (metres = 11%; car lengths = 32%); and combinations of time and distance (1%). No one reported having received an infringement for not keeping a safe following distance, although 29% reported being involved in a crash where their vehicle hit the one in front. The majority (86%) reported that it was somewhat-extremely unlikely they would be caught by police if following too closely, indicating a perceived lack of enforcement for this offence. Reasons for this included perceptions of difficulty for police to enforce this offence (5%), not having heard of anyone being caught for this offence (17%), and other police priorities (30%). Conclusions This study is part of a larger research project that aims to improve knowledge about driving conditions, patterns and locations, and driver behaviours that lead to driving at unsafe headways (i.e. following too closely). Recommendations for use of these findings to inform driver education and awareness campaigns are discussed.

Doppler and pathloss characterization for vehicle-to-vehicle communications at 5.8 GHz

Due to significant increase in vehicular accident and traffic congestions, vehicle to vehicle (V2V) communication based on the intelligent transport system (ITS) was introduced aiming to significantly reduce vehicular accident and traffic congestion. However, to carry out efficient design and implementation of a reliable vehicular communication systems, a deep knowledge of the propagation channel characteristics in different environments is crucial, in particular the Doppler and pathloss parameters. This paper presents an empirical V2V channel characterization and measurement performed under realistic urban, suburban and highway driving conditions in Brisbane, Australia. Based on Lin Cheng statistical Doppler Model (LCDM), values for the RMS Doppler spread and coherence time due to time selective nature of V2V channels are presented. Also, based on log-distance power law model, values for the mean pathloss exponent and the standard deviation of shadowing were reported for urban, suburban and highway environments. The V2V channel parameters can be useful to system designers for the purpose of evaluating, simulating and developing new protocols and systems.