conference paper

Prediction of short-term freeway traffic volume using recursive least squares and lattice filtering

Applications of advanced technologies in transportation

Publication Date

January 1, 1998

Abstract

Estimating and predicting the dynamic variation of traffic variables such as volume and speed is becoming increasingly important for intelligent transportation systems applications. In this paper, we present a linear model for the short-term (30 second) prediction of freeway traffic volumes using a recursive least squares algorithm with a lattice filter. An innovative feature of the model is that all of the parameters, such as the optimal weights and the model order, are time-varying and are automatically updated in real-time so that unexpected traffic variations can be addressed by varying the parameters. Recursive filtering algorithms are applied in order to save computation time and storage space. The results of the performance analysis show that the proposed model works well under different conditions, including multiple locations and recurrent and non-recurrent congestion.

Suggested Citation
SM Kang, SG Ritchie and R Jayakrishnan (1998) “Prediction of short-term freeway traffic volume using recursive least squares and lattice filtering”, in . Hendrickson, CT and Ritchie, SG (ed.) Applications of advanced technologies in transportation. AMER SOC CIVIL ENGINEERS, pp. 255–264.

published journal article

Socioeconomic Disparities of Low-Cost Air Quality Sensors in California, 2017–2020

American Journal of Public Health

Publication Date

March 1, 2022

Author(s)

Yi Sun, Amirhosein Mousavi, Shahir Masri, Jun Wu

Abstract

Objectives. To (1) examine the disparity in availability of PurpleAir low-cost air quality sensors in California based on neighborhood socioeconomic status (SES) and exposure to fine particulate matter smaller than 2.5 micrometers (PM2.5), (2) investigate the temporal trend of sensor distribution and operation, and (3) identify priority communities for future sensor distribution. Methods. We obtained census tract–level SES variables and PM2.5 concentrations from the CalEnviroScreen4.0 data set. We obtained real-time PurpleAir sensor data (July 2017–September 2020) to examine sensor distribution and operation. We conducted spatial and temporal analyses at the census tract level to investigate neighborhood SES and PM2.5 concentrations in relation to sensor distribution and operation. Results. The spatial coverage and the number of PurpleAir sensors increased significantly in California. Fewer sensors were distributed in census tracts with lower SES, higher PM2.5, and higher proportions of racial/ethnic minority populations. Furthermore, a large proportion of existing sensors were not in operation at a given time, especially in disadvantaged communities. Conclusions. Disadvantaged communities should be given access to low-cost sensors to fill in spatial gaps of air quality monitoring and address environmental justice concerns. Sensor purchasing and deployment must be paired with regular maintenance to ensure their reliable performance. (Am J Public Health. 2022;112(3):434–442. https://doi.org/10.2105/AJPH.2021.306603)

Suggested Citation
Yi Sun, Amirhosein Mousavi, Shahir Masri and Jun Wu (2022) “Socioeconomic Disparities of Low-Cost Air Quality Sensors in California, 2017–2020”, American Journal of Public Health, 112(3), pp. 434–442. Available at: 10.2105/AJPH.2021.306603.

published journal article

Violence associated with combat-related posttraumatic stress disorder: The importance of anger.

Psychological Trauma: Theory, Research, Practice, and Policy

Publication Date

January 1, 2015

Author(s)

Raymond Novaco, Claude M. Chemtob
Suggested Citation
Raymond W. Novaco and Claude M. Chemtob (2015) “Violence associated with combat-related posttraumatic stress disorder: The importance of anger.”, Psychological Trauma: Theory, Research, Practice, and Policy, 7(5), pp. 485–492. Available at: 10.1037/tra0000067.

research report

Optimal sensor locations for advanced truck surveillance on California freeways

Publication Date

September 1, 2013

Author(s)

Jae Young Jung, Andre (Yeow Chern) Tok, Stephen Ritchie, Irvine University of California

Abstract

A new hybrid sensor technology integrating existing Weigh-In-Motion (WIM) axle configuration data with inductive signature data obtained from advanced Inductive Loop Detector (ILD) is gaining interest due to its potential to provide detailed classification of truck body types as well as anonymous tracking of truck movements on freeways. This paper describes the methodologies and analysis of two alternative strategies for optimal deployment locations for this new technology at existing WIM locations by utilizing sampled truck GPS trajectories on California freeways: (1) Flow-interception approach to maximize the total amount of net origin-destination (OD) flows captured; (2) Re-identification approach to maximize insights into origins and destinations of sampled truck trips, as well as routes of those trips. The truck GPS samples used in this study is obtained from the American Transportation Research Institute (ATRI), which provides position and time stamp information of truck movements. The model designed for flow-interception is capable of selecting locations emphasizing different body types by employing the flow-based weight factor. The RSP model investigates the best locations for heavy truck movement identification on freeways by selecting pairwise locations, and is shown to be sensitive to the re-identification decay factor assumed.

Suggested Citation
Jaeyoung Jung, Andre Tok, Stephen G. Ritchie and Irvine University of California (2013) Optimal sensor locations for advanced truck surveillance on California freeways, p. 21p.

conference paper

Applications of speed variance in measuring freeway level of service and in air emissions evaluation

Proceedings of the 93rd annual meeting of the transportation research board

Publication Date

January 1, 2014

Abstract

Speed variance is an important, but overlooked, parameter in traffic studies. This paper examines the use of statistical relationships between speed variance and the fundamental parameters-density, average speed, and flow-to support applications of speed variance via those fundamental parameters to two important aspects of traffic operations. First, it is proposed that speed variance be used to measure freeway level of service from A through E in the context of “no more x% of the vehicles with travel time up to y% greater than the free flow condition.” It is argued that such a measure not only reflects mobility (y%), reliability (x%), and potentially safety, but also avoids the vague descriptions associated with each service level in the current HCM. Second, the relationships are applied to estimate speed distribution for the MOVES mobile source air emission model. A revised approach is developed and compared to that in the current model. It is argued that the MOVES model’s approach limits the distribution in two speed bins, results in unsupported speed variance, and may cause identical distributions under various average speeds. The proposed revised approach based on speed variance generates specific spread-out distributions consistent with empirical data. The findings of these two applications bring new concepts to the current practice. Suggestions are made to fix the deficiencies of the existing and proposed approaches in the applications.

Suggested Citation
Chih-Lin Chung and Will Recker (2014) “Applications of speed variance in measuring freeway level of service and in air emissions evaluation”, in Proceedings of the 93rd annual meeting of the transportation research board, p. 20p.

conference paper

An analysis of the timing of truck and car accidents in a busy freight corridor

Proceedings of the 91st annual meeting of the transportation research board

Publication Date

January 1, 2012

Abstract

The objective of this study is to understand the timing of truck and car accidents in a busy freight corridor (I-110 and I-710 freeways) that connects the Ports of Los Angeles and Long Beach to nearby intermodal rail and trans-loading facilities, and various warehouses. The authors analyze 16,417 accidents that occurred between 2005 and 2007 on these two freeways in Los Angeles County, California; approximately 14.5 percent of these accidents involved trucks. Vehicle Miles Traveled (VMT) data were collected from the Freeway Performance Measurement System (PeMS) to compute hourly and monthly car and truck accident rates for both freeways in both traffic directions. Kolmogorov-Smirnov and CramÃrâ??von Mises goodness of fit tests were then calculated to test whether directional accident probabilities are similar or not and whether the risk of an accident is time dependent. The authors found that the probability of an accident involving only cars is highest after midnight (the peak probability occurs between 1 AM and 3 AM for both freeways) while the probability of an accident involving a truck is highest during mid-day (the peak probability occurs between 8 AM and 4 PM for both freeways). These results have implications for programs that attempt to move truck deliveries during off-peak hours such as the PierPass program implemented by the Ports of Los Angeles and Long Beach..

Suggested Citation
Ankoor Bhagat, Jean-Daniel Saphores and R. Jayakrishnan (2012) “An analysis of the timing of truck and car accidents in a busy freight corridor”, in Proceedings of the 91st annual meeting of the transportation research board, p. 16p.

published journal article

Development of expert systems technology in the California Department of Transporation

Transportation Research Record

Publication Date

January 1, 1988

Author(s)

Stephen Ritchie, Louis F. Cohn, Roswell A. Harris

Abstract

This paper presents the results of a research project the principal objective of which was to prepare a plan for the development and implementation of knowledge-based expert systems (KBES) projects throughout th.e California Department of Transportation (Caltrans). A major part of the project involved development of a special questionnaire and conduct of 50 in-depth interviews of Caltrans senior managers and engineers to identify candidate projects. Forty-five such projects were identified and ranked by priority. In addition, the following aspects were addressed: resource and time requirements for each KBES project, hardware and software needs to best accommodate implementation throughout Caltrans, and recommendations for training. Caltrans has now begun implementation of the plan developed in this research. A major new KBES research project on hazardous waste management has been initiated and is also discussed in this paper.

Suggested Citation
Stephen G. Ritchie, Louis F. Cohn and Roswell A. Harris (1988) “Development of expert systems technology in the California Department of Transporation”, Transportation Research Record, (1187), pp. 21–29. Available at: https://onlinepubs.trb.org/Onlinepubs/trr/1988/1187/1187-003.pdf.

published journal article

Real-time estimation of accident likelihood for safety enhancement

Journal of transportation engineering

Publication Date

January 1, 2005

Author(s)

Jun-Seok Oh, Cheol Oh, Stephen Ritchie, Myungsoon Chang
Suggested Citation
Jun-Seok Oh, Cheol Oh, Stephen G. Ritchie and Myungsoon Chang (2005) “Real-time estimation of accident likelihood for safety enhancement”, Journal of transportation engineering, 131(5), pp. 358–363.

Preprint Journal Article

SlowPerception: Physical-World Latency Attack against Visual Perception in Autonomous Driving

Publication Date

July 19, 2024

Author(s)

Chen Ma, Ningfei Wang, Zhengyu Zhao, Qi Alfred Chen, Chao Shen

Abstract

Autonomous Driving (AD) systems critically depend on visual perception for real-time object detection and multiple object tracking (MOT) to ensure safe driving. However, high latency in these visual perception components can lead to significant safety risks, such as vehicle collisions. While previous research has extensively explored latency attacks within the digital realm, translating these methods effectively to the physical world presents challenges. For instance, existing attacks rely on perturbations that are unrealistic or impractical for AD, such as adversarial perturbations affecting areas like the sky, or requiring large patches that obscure most of a camera’s view, thus making them impossible to be conducted effectively in the real world. In this paper, we introduce SlowPerception, the first physical-world latency attack against AD perception, via generating projector-based universal perturbations. SlowPerception strategically creates numerous phantom objects on various surfaces in the environment, significantly increasing the computational load of Non-Maximum Suppression (NMS) and MOT, thereby inducing substantial latency. Our SlowPerception achieves second-level latency in physical-world settings, with an average latency of 2.5 seconds across different AD perception systems, scenarios, and hardware configurations. This performance significantly outperforms existing state-of-the-art latency attacks. Additionally, we conduct AD system-level impact assessments, such as vehicle collisions, using industry-grade AD systems with production-grade AD simulators with a 97% average rate. We hope that our analyses can inspire further research in this critical domain, enhancing the robustness of AD systems against emerging vulnerabilities.

Suggested Citation
Chen Ma, Ningfei Wang, Zhengyu Zhao, Qi Alfred Chen and Chao Shen (2024) “SlowPerception: Physical-World Latency Attack against Visual Perception in Autonomous Driving”. arXiv. Available at: 10.48550/arXiv.2406.05800.

conference paper

On Adversarial Robustness of Trajectory Prediction for Autonomous Vehicles

Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition

Publication Date

January 1, 2022

Author(s)

Qingzhao Zhang, Shengtuo Hu, Zhe (Jared) Sun, Qi Alfred Chen, Z. Morley Mao
Suggested Citation
Qingzhao Zhang, Shengtuo Hu, Jiachen Sun, Qi Alfred Chen and Z. Morley Mao (2022) “On Adversarial Robustness of Trajectory Prediction for Autonomous Vehicles”, pp. 15159–15168. Available at: https://openaccess.thecvf.com/content/CVPR2022/html/Zhang_On_Adversarial_Robustness_of_Trajectory_Prediction_for_Autonomous_Vehicles_CVPR_2022_paper.html (Accessed: October 5, 2023).