Browsing by Author "Ahmed, Hafiz Usman"

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Calibration of Smartphone Sensors to Evaluate the Ride Quality of Paved and Unpaved Roads
(2020) Yang, Xinyi; Hu, Liuqing; Ahmed, Hafiz Usman; Bridgelall, Raj; Huang, Ying; Upper Great Plains Transportation Institute
Transportation agencies report that millions of crashes are caused by poor road conditions every year, which makes the localization of roadway anomalies extremely important. Common methods of road condition evaluation require special types of equipment that are usually expensive and time-consuming. Therefore, the use of smartphones has become a potential alternative. However, differences in the sensitivity of their inertial sensors and their sample rate can result in measurement inconsistencies. This study validated those inconsistencies by using three different types of smartphones to collect data from the traversal of both a paved and an unpaved road. Three calibration methods were used including the reference-mean, reference-maximum, and reference-road-type methods. Statistical testing under identical conditions of device mounting using the same vehicle revealed that the roughness indices derived from each device and road type are normally distributed with unequal means. Consequently, applying a calibration coefficient to equalize the means of the distributions of roughness indices produced from any device using the reference mean method resulted in consistent measurements for both road types.
Effects of smartphone sensor variability in road roughness evaluation
(2021) Ahmed, Hafiz Usman; Hu, Liuqing; Yang, Xinyi; Bridgelall, Raj; Huang, Ying; Upper Great Plains Transportation Institute
Accelerometers embedded in smartphones have become an alternative means of measuring the roughness of roads. However, the differences in their sensitivity and sampling rates between smartphones could produce measurement inconsistencies that challenge the wide spread of the smartphone approach for road roughness measurements. In this study, the roughness measurement inconsistency was investigated between smartphones from three different brands. Using the same vehicle, device mount method, traversal speed, and method of producing a roughness index, field experiments demonstrated that accelerometer sensitivities and maximum sample rates vary significantly among smartphones of the same brand as well as across brands. For each smartphone, to achieve a margin-of-error within a 95% of confidence, significant large amounts of traversals are needed. Specifically, 24 and 35 traversals for a paved and an unpaved road, respectively. A higher sampling rate produced more consistent measurements and the least margin-of-error but resulted in larger data sizes. In addition, the measurements from all smartphones were not very sensitive to the size of the feature extraction window, therefore, selecting the largest practical window size will minimize the data size without significant loss of accuracy. For practical application, calibration is necessary to achieve consistent roughness measurements between various different smartphones.
Evaluating the Safety and Mobility of the Cumulative-Anticipative Car-Following Model for Connected Autonomous Vehicles
(North Dakota State University, 2020) Ahmed, Hafiz Usman
The advancements of vehicle automation are progressively improving resulting in safer driving environments in addition to more efficient mobility and fuel cost savings. However, autonomous and connected autonomous vehicles (AVs, CAVs) require decades to achieve complete market penetration. It is important to investigate the coexistence of conventional and autonomous cars during such a transition period. Traditionally, adaptive cruise control (ACC) and cooperative ACC (CACC) models were used for the AVs to guide their car-following. Recently, the cumulative-anticipative car-following (CACF) model was developed with consideration of the cumulative influences from surrounding vehicles through vehicle-to-everything (V2X) communication. This study further evaluates the safety and mobility performances of the CACF model for CAVs in mixed traffic through various sensitivity tests using the VISSIM simulation platform. The results demonstrate that the CACF model has promising improvements in roadway safety and network performances compared with the Wiedemann 99 and CACC models in mixed environments.
Technology Developments and Impacts of Connected and Autonomous Vehicles: An Overview
(2022) Ahmed, Hafiz Usman; Huang, Ying; Lu, Pan; Bridgelall, Raj; Upper Great Plains Transportation Institute
The scientific advancements in the vehicle and infrastructure automation industry are progressively improving nowadays to provide benefits for the end-users in terms of traffic congestion reduction, safety enhancements, stress-free travels, fuel cost savings, and smart parking, etc. The advances in connected, autonomous, and connected autonomous vehicles (CV, AV, and CAV) depend on the continuous technology developments in the advanced driving assistance systems (ADAS). A clear view of the technology developments related to the AVs will give the users insights on the evolution of the technology and predict future research needs. In this paper, firstly, a review is performed on the available ADAS technologies, their functions, and the expected benefits in the context of CVs, AVs, and CAVs such as the sensors deployed on the partial or fully automated vehicles (Radar, LiDAR, etc.), the communication systems for vehicle-to-vehicle and vehicle-to-infrastructure networking, and the adaptive and cooperative adaptive cruise control technology (ACC/CACC). Secondly, for any technologies to be applied in practical AVs related applications, this study also includes a detailed review in the state/federal guidance, legislation, and regulations toward AVs related applications. Last but not least, the impacts of CVs, AVs, and CAVs on traffic are also reviewed to evaluate the potential benefits as the AV related technologies penetrating in the market. Based on the extensive reviews in this paper, the future related research gaps in technology development and impact analysis are also discussed.