Maximum Lateral Acceleration Research Articles

Enhancing highway Loop Safety Level through proactive risk-based assessment of geometric configuration using lateral acceleration

Objective Loop ramps are complex due to their combination of horizontal curves and vertical alignments. Analyzing driving behavior and measuring safety levels can provide insights for designers, helping to improve the performance and alignment of design assumptions with actual driving behavior on loops. Therefore, the primary objective of this research is to explore the safety, performance and geometric configuration of the main body and general shape of free-flow loop ramps in the free-following mode. Methods The study uses data from a UAV to investigate vehicle demand behavior. Maximum lateral acceleration (a y,i) in loops is used as a Surrogate Safety Measure (SSM), along with a new parameter, the a/b ratio, to determine the general shape of loop bodies. The study presents the Loop Safety Level (LSL), an approach for proactive risk analysis and ranking that relies on threshold lateral acceleration (a t), 85th percentile maximum lateral acceleration ( a y,max,85%), and crash analysis. Results A higher LSL value points to a more critical safety concern regarding the loop’s shape in relation to lateral acceleration caused by driving behaviors. Comparing crash statistics with lateral acceleration results enables the LSL to provide appropriate safety ratings and diagnose loop segment safety. A prediction model for maximum lateral acceleration, based on loop geometry, demonstrates a good fit (R2=0.88) between observed and predicted data. Conclusions The study enhances understanding of safety considerations in geometric configuration and general shape enhancement of loops during the design process.

The effect of load-dependent tyre friction and aerodynamic cross-flow forces on the g-g maps and minimum-lap-time of motorcycles

A three-dimensional quasi-steady-state free-trajectory method based on semi-analytical g-g maps has been recently proposed to simulate the minimum-time manoeuvring of road vehicles. A number of assumptions, such as identical tyre-road friction coefficients on front and rear tyres and negligible aerodynamic cross-flow forces (i.e. downforces and sideforces), were enforced in the case of motorcycles to keep the g-g maps semi-analytical. Such assumptions are lifted in this work and their effect on the g-g maps of single-track vehicles is analysed, together with the consequences on the related minimum-lap-time simulations. The examples of application are carried out on the Mugello circuit and compared with previous findings in the literature. It is found that different friction coefficients on tyres call for different braking strategies to extract the maximum performance of the vehicle (when compared against the case with equal friction coefficients), while aerodynamic downforces can reduce stoppie and wheelie problems, improve acceleration and braking performance and increase the maximum lateral acceleration achievable. However, if the resulting cross-flow force lies on the plane of the bike the maximum lateral performance could be reduced, depending on tyre properties.

Pedestrian-induced lateral vibration of footbridges: A comparison study of different loading models

The pedestrian-induced lateral vibration of footbridges has attracted much attention since the London Millennium Bridge incident. Significant investigations were mainly performed by external-excited force models and self-excited force models. The first type models consider pedestrians as harmonic forces and/or spring-mass-damping (SMD) systems. The second type consider the self-excited forces of pedestrians that initialize the instability of footbridges by e.g. applying the inverted pendulum (IP) model. This study compares performance of different models in reproducing the observed results of typical living footbridges: the London Millennium Bridge (UK), T-bridge (Japan) and Pedro e Inês footbridge (Portugal). With varying step frequencies and pedestrian numbers, both the acceleration time history and the discrepancy between the input work and consumed work exhibit a consistent trend for the harmonic force (HF) model and SMD model, yet a notable difference for the IP model. The HF model and SMD model are better suited for assuming synchronization, making them convenient for estimating the serviceability of pedestrian-induced lateral vibration. On the other hand, the IP model is more appropriate for incorporating random step frequencies and can better capture observed instability phenomena realistically. Because the SMD model with (inconsistent) parameters from literature may result in significant differences in predicting the acceleration amplitudes, this paper modifies the SMD model and proposes a pedestrian synchronization ratio formula as an exponential function of the maximum lateral acceleration. It is validated by comparing the analytical and numerical results for the three footbridges. Furthermore, by the modified SMD model, the lateral lock-in phenomenon of footbridges is simulated reliably and conveniently. This work contributes to analyze pedestrian-induced lateral vibration of footbridges.

A survey on countermeasures of railway vehicle stability decrease caused by the evolution of hollow-worn wheels

With the problem that the lateral vibration acceleration of the frame of a certain type of Electric Multiple Units (EMU) gradually approaches the limit value as the running mileage increases, the tracking test was conducted on the whole vehicle’s wheel tread wear and the frame’s vibration response. It was found that as the tread hollow-worn increased, the vehicle stability would deteriorate. In order to improve vehicle stability, an optimisation method of EMU stability is proposed based on controlling the evolution of hollow-worn wheels. The results show that after optimisation by this method, the hollow-worn state of the wheel tread is significantly improved; the equivalent conicity of the worn wheel is reduced by 16.39%, and the maximum lateral vibration acceleration of the frame is reduced by 32.02%, so the vehicle stability is also significantly improved; meanwhile, the ride comfort and safety of the vehicle still meet the requirements of the standard.

Impacts of g-g-v Constraints Formulations on Online Minimum-Time Vehicle Trajectory Planning

The g-g-v diagram is a popular representation of a vehicle’s maximum longitudinal and lateral accelerations, as a function of its speed. Recently, g-g-v diagrams have been used as performance constraints for online minimum-time vehicle trajectory planning with economic nonlinear model predictive control (E-NMPC). However, in the related literature, the modeling accuracy of the g-g-v formulations was often compromised in favor of computational efficiency for online E-NMPC. This paper compares various formulations of the g-g-v constraints, evaluating their accuracy, computational efficiency and impact on the lap times, when applied by an artificial race driver (ARD) to control a sports car model on a circuit. Also, we propose a new g-g-v diagram formulation, based on convex polytopic and non-convex polynomial constraints. Our formulation yields improved modeling accuracy while preserving a low computational burden for online E-NMPC. Finally, we analyze the vehicle trajectories, to understand how ARD achieves lower lap times through an improved knowledge of the maximum performance.

Sinusoidal Guidance

This work presents a novel three-point guidance strategy that simultaneously achieves a desired impact angle, launch angle, impact time, and maximum lateral acceleration against a stationary target. The guidance strategy uses four sinusoidal harmonics of different amplitudes to construct an interceptor trajectory that satisfies all the mission specifications. A new geometric constant G for sinusoids is proposed, which requires only the interceptor’s line-of-sight angles from the launcher and the target for computation. Correspondingly, a geometric rule is developed—the interceptor follows the desired sinusoidal trajectory by maintaining G=0 throughout the engagement. A trajectory design algorithm to determine the desired sinusoidal trajectory based on the mission specifications is presented. A proportional-derivative controller is applied to implement the proposed geometric rule, and analytical expressions for the controller gains are defined. The efficacy of the guidance strategy is investigated via various simulation scenarios. It is shown that the developed guidance law is robust to the initial heading errors and interceptor dynamics.

Conceptual Design and Energy Efficiency Evaluation for a Novel Torque Vectoring Differential Applied to Front-Wheel-Drive Electric Vehicles

This paper presents a novel differential with lateral torque vectoring activated by an auxiliary motor, called motor-modulated lateral torque vectoring differential, or briefly, MLTD. Its architecture and kinematic characteristics are described, and the optimal cornering performance due to torque vectoring is evaluated using a steady-state vehicle dynamic model. Then, a conceptual design case of MLTD installed in a front-wheel-drive electric vehicle is conducted to assess its feasibility in terms of cornering, driving performances, and energy efficiency performance. The calculations show that an optimal distribution ratio between left and right torques for maximum lateral acceleration can be obtained for a specific cornering condition, further used for DM sizing in the preliminary stage. The simulations for energy consumption at constant-speed turning reveal that energy efficiencies of MLTD are lower than those of conventional differentials with evenly distributed torques. However, this deficiency may be paid off by moderately cutting down the rolling resistance of tire while the superior cornering performances brought by torque vectoring is still preserved. Accordingly, the newly proposed MLTD possesses greater flexibility to improve energy efficiency and driving range of electric vehicles without trading off against its desirable cornering performance and safe handling, and is thus worthy of further development.

Reducing vehicle-bridge coupled vibration of a new-type maglev vehicle with mid-mounted suspension on curve via forced guidance device

To reduce the vehicle-bridge coupled vibration of a new-type maglev vehicle with mid-mounted suspension (MVMS) on a curve and increase its curve-passing speed, the forced guidance device (FGD) for MVMS is designed and the effectiveness of the FGD is proved. Firstly, on the basis of the FGD for HSST (High Speed Surface Transport) maglev vehicle and the geometric relationship between the movable sliders and the cabin as MVMS passes through a curved track, the FGD scheme for MVMS was designed. Secondly, the dynamic models with 5-bogies MVMSs (with and without FGD), control system, 11 flexible bridges, and track irregularities were established. Finally, the vehicle-bridge coupled vibration response of MVMSs on the curved track was analysed. Results show that the accelerations of the bridges, levitation modules, and cabin can be reduced significantly by installing FGD, especially at higher speeds. Compared to the accelerations without FGD, the maximum lateral and vertical accelerations of each bridge midspan can be reduced respectively by 56% and 43% at the speed of 45 km/h, those of the levitation modules can be reduced by 48% and 90%, respectively, and those of the cabin can be reduced by 37% and 53%, respectively.

Seismic response and liquefaction characteristics of wide and shallow multi-bucket jacket foundation under scour conditions

Scour has a significant effect on the seismic response of offshore structures. Compared to monopiles, MBJFs are shallow foundations and scouring has a more detrimental effect on their earthquake performance. However, the combined impacts of scour and earthquake on the structural response and liquefaction characteristics of the MBJFs have not been completely investigated. Based on the secondary development of the ABAQUS program, this paper proposes a method for calculating the seismic response and liquefaction of MBJF under local scour conditions. The seismic response and liquefaction characteristics of MBJF-supported OWTs in silty soil are evaluated under different scour depths, scour ranges, earthquake motions, soil conditions, and structural damping. In comparison to the unscoured condition, the results show that the maximum horizontal displacement, lateral acceleration, and bending moment of MBJF-supported OWTs increase by 30%, 97%, and 58%, respectively. Liquefaction is generated mostly in the soil outside the bucket rather than inside. An increase in soil density can improve the lateral acceleration of the structure and reduce the proportion of liquefaction in the soil. The maximum reduction in liquefaction can be 70.2% for an increase of 23% in soil densities. Disregarding structural damping will overestimate the structural response and the proportion of soil liquefaction. The findings may shed light on the seismic response and liquefaction characteristics of MBJF-supported OWTs located in complex offshore scour environments.

Dynamic interactions of tram-turnout coupling system in embedded turnout area

Embedded turnout is one of the key facilities in the embedded track network of modern tram systems. In this study, the damping performance and track stiffness of an embedded turnout are tested on site. A multi-rigid body dynamics model of the tram and a finite-element dynamics model of the embedded turnout are established, and the two models are coupled based on the wheel-rail contact theory for the turnout area. Next, the dynamic responses of the tram passing through the embedded turnout are analyzed. The results show that the embedded turnout has favorable damping performance. The high stiffness of variable section rails at the switch and frog would lead to an increase in the wheel-rail dynamic force. When the tram passes through the embedded turnout, the wheel-rail vertical force reaches maximum values of 106.3 and 35.2 kN at the frog and switch, respectively; the maximum wheel derailment coefficient and wheel weight reduction rate are 0.49 and 0.57, respectively, which are within the safety limit specified in the Standards; the maximum lateral and vertical vibration accelerations of the tram body are 0.38 and 0.71 m/s2, respectively, satisfying the comfort requirements; the wheel–rail wear work at the switch is greater than that at the frog.

A novel collision warning system based on the visual road environment schema: An examination from vehicle and driver characteristics

Drivers pay unequal attention to different road environmental elements and visual fields, which greatly influences their driving behavior. However, existing collision warning systems ignore these visual characteristics of drivers, which limits the performance of collision warning systems. Therefore, this study proposes a novel collision warning system based on the visual road environment schema, in order to enhance the support for avoiding potential dangers in objects and areas that are easily overlooked by the drivers’ vision. To capture the above visual characteristics of drivers, the visual road environment schema that consists of the semantic layer, the scene depth layer, the sensitive layer, and the visual field layer is established by using several different deep neural networks, which realizes the recognition, quantization, and analysis of the road environment from the drivers’ visual perspective. The effectiveness of the novel collision warning system is verified by the driving simulation experiment from six indicators, including warning distance, maximum lateral acceleration, maximum longitudinal deceleration, minimum collision time, reaction time, and heart rate. Additionally, a grey target decision-making model is built to comprehensively evaluate the system. The results show that compared with the traditional collision warning system, the novel collision warning system proposed in this study performs significantly better and can discover potential dangers earlier, give timely warnings, enhance the vehicles’ lateral stability and driving comfort, shorten reaction time, and relieve the drivers’ nervousness. By integrating the drivers’ visual characteristics into the collision warning system, this study could help to optimize the existing collision warning system and promote the mutual understanding between intelligent vehicles and human drivers.

Accuracy requirements for the road friction coefficient estimation of a friction-adaptive automatic emergency steer assist (ESA)

The number of traffic accidents resulting in personal injury and property damage is increasingly being reduced by effective advanced driver assistance systems (ADAS). Nevertheless, many traffic accidents still cannot be prevented today because they are due to wet, snow- and ice-covered roads. For this reason, the Institute of Automotive Engineering (IAE) of the Technical University of Braunschweig is investigating the road friction coefficient sensitivity and adaptation of advanced driver assistance systems (ADAS) currently in series production from 2018 to 2021 as part of the ‘Road Condition Cloud’ research project funded by the German Research Foundation (DFG) to increase driving safety, particularly on wet, snow- and ice-covered roads. In this article, the road friction coefficient sensitivity and adaptation of an automatic emergency steer assist is simulatively investigated. This assist overrides the driver to automatically execute an evasive maneuver. The driving maneuver used is a standardized obstacle-avoidance maneuver that is simulatively repeated on a dry, wet, snow- and ice-covered road. The road friction coefficient sensitivity shows that this test is already failed on a wet road because the simulated vehicle does not pass the second lane without errors. Subsequently, a road friction coefficient adaptation of the emergency steer assist is investigated. This adaptation varies the maximum lateral acceleration of the evasive trajectory depending on an estimated value of the road friction coefficient in order not to exceed the maximum adhesion coefficient of the wheels during the evasive maneuver. Ideally, the estimated value matches the true road friction coefficient so that the second lane is passed without errors even on a wet, snow- and ice-covered road. In contrast, an existing difference determines whether the second lane is reached. Finally, the necessary accuracy requirements of the road friction coefficient estimation are determined in an novel estimation error diagram. A road friction coefficient adaptation increases the driving safety of driver advanced assistance systems (ADAS) that are in series production today and future highly automated driving functions (HAF) and is necessary for automated driving because the driver is not present as a fallback level. The described results were presented before in [1].

Towards Bi‐Dimensional driver models for automated driving system safety requirements: Validation of a kinematic model for evasive lane‐change maneuvers

AbstractPreventing traffic accidents is of paramount importance for society's well‐being. The topic is particularly relevant for driving automation given the high expectations about automated vehicles and the difficulty in estimating reliable safety figures for those complex systems. Under this premise, the present manuscript investigates how to derive a safety benchmark model for evasive lane‐change maneuvers that can also be applied in microsimulation frameworks. The approach leverages a jerk‐limited bang‐bang kinematic model for lane‐change and validates its minimum time prediction against other kinematic approaches and vehicle dynamical models based on a robust minimum‐time optimal control formulation. It is shown how kinematic modeling does not embrace steering angle constraints (at low‐speed) and misses the inertia effect (at high‐speed) thus introducing discrepancies. However, due to the introduction of a braking model, it can be safely claimed that the low‐speed discrepancy between the kinematic and the dynamic models lies in a region where stopping is still the most efficient reaction. Moreover, a method is shown to compute the effective lateral acceleration for a kinematic model to match the dynamical system's maneuvering. The kinematic lane‐change model can thus constitute a valid performance benchmark provided that conservative assumptions are used when calibrating its maximum lateral acceleration.

An optimal control approach to the computation of g-g diagrams

The so-called g-g diagram is widely employed to assess the performance of road vehicles since it provides the maximum longitudinal and lateral accelerations that can be extracted from the selected vehicle. The different points of the g-g diagram are usually computed independently from one another, e.g. the maximum longitudinal accelerations corresponding to given lateral accelerations are computed sequentially. In this work, the problem of computing the points of the g-g diagram is transformed into an optimal control problem, which allows to avoid one of the most annoying practical problems often encountered when deriving such diagrams, namely the ‘jumps’ between different solutions (i.e. large slip vs. small slip solutions at similar lateral acceleration) in adjacent points along the g-g envelope. In the proposed method, the objective is to maximise the area enclosed within the g-g diagram, which has a polar representation. The rate of change of the radial coordinate is the control input. Additional constraints are included to enforce the continuity between the states of the vehicle model in adjacent points along the envelope. These conditions can hardly be enforced using standard methods based on sequential and independent computation of the g-g points. An example of the application of the method is demonstrated on the classic double-track car model with nonlinear tyres.

Anti-Rollover Control and HIL Verification for an Independently Driven Heavy Vehicle Based on Improved LTR

The rollover evaluation index provides an important threshold basis for the anti-rollover control system of vehicle. Regarding the rollover risk of independently driven heavy-duty vehicles, a new rollover evaluation index is proposed, and the feasibility of the improved index was verified through hierarchical control and HIL (hardware-in-the-loop) experiments. Based on an 18-DOF spatial dynamics model of a heavy-duty vehicle, the improved LTR (load transfer rate) index was obtained to describe the dynamic change in the tire’s vertical load. It replaces the suspension force and the vertical inertia force of the unsprung load mass. It avoids the problem of directly measuring or estimating the vertical load in the LTR index. Under the conditions of fishhooking and angle stepping, three types of rollover indicators were compared, and the proposed index can more sensitively identify the likelihood of rollover. In order to apply the improved rollover index to a rollover control well, a hierarchical controller based on the identification of the slip rate of the road surface, ABS control with sliding mode, variable structure and differential braking was designed. Simulations and HIL tests proved that the designed controller can accurately predict the rollover risk and avoid the rollover in time. Under the condition of J-turning, the yaw rate, slip angle and maximum lateral acceleration are reduced by 9%, 16% and 3%, respectively; under the condition of fishhooking, the maximum yaw rate, slip angle and lateral acceleration are reduced by 12%, 18% and 3%, respectively.

Effectiveness and Kinematic Analysis of Initial Step Patterns for Multidirectional Acceleration in Team and Racquet Sports.

The ability for quick multidirectional accelerations is crucial for athletic performance in team and racquet sports. So far, there has been little research dedicated to different initial step patterns usually applied by players. Therefore, the present study investigated the kinematic characteristics and effectiveness of the following step patterns: Jab Step (JS), Pivot Step (PS), Gravity Step (GS) and Counter Step (CS). Twenty-two male competitive team and racquet sport athletes completed maximum lateral accelerations utilizing the step patterns. Following familiarization with each step pattern, three 5 m sprints (5 m STs) into both directions (left & right) were completed. Sprint times, the translation of the center of mass (CoM) and joint angles were obtained using three-dimensional motion analysis. 5 m STs of the CS were faster compared to the GS and PS for both directions. A detailed distance-time analysis revealed that for shorter distances only the JS was faster than the GS. Regarding the sequence in which the maximum angular velocities (max. ) in the hip, the knee, and the ankle were reached during the push off, there was a proximal-to-distal sequence for the JS and the CS, but a distal-to proximal sequence for the GS and the PS. The results reveal that the JS and the CS are superior for accelerations towards the lateral direction. Specifically, they indicate that the JS is more suitable for covering very short distances and the CS is superior for covering further distances. In addition, the distal-to-proximal sequence of max. during the push-off in the GS and the PS might indicate lower kinematic efficiency.

Cornering Force Maximization With Variable Slip Ratio Control for Independent-All-Wheel-Drive Electric Vehicle

The improvement of the maneuverability using fast and precise control of the electric motor is a crucial subject. A driving force controller (DFC) is considered to be a simple yet excellent method to secure the traction of the tire by directly limiting the slip ratio of the wheel. A conventional variable slip ratio limiter (VSRL) used for the DFC changed the limit value according the sideslip angle of the wheel, effectively maximizing either longitudinal or lateral forces of the tire. However, this did not necessarily maximize the cornering force, which is perpendicular to the vehicle body speed vector. This study presents a new variable slip ratio control method to maximize the cornering forces when the wheels have a large sideslip angle, with the aim of increasing maximum available lateral acceleration. An improved VSRL is proposed so that even when the sideslip angle of the tire is large, the tire force direction faces perpendicular to the vehicle body speed vector and the cornering force can be maximized. Simulations and experimental results using a real EV confirm that cornering maneuverability can be improved, increasing the yaw rate and lateral acceleration during cornering with a large sideslip angle of the tire on slippery roads.

Preliminary driving style classification of the professional drivers

Driving style and driver behaviour are important in evaluating city bus drivers. Buses are one of the means of public transportation in cities, used by millions of people. The purpose of this study was to present a model for preliminary classification of driving style of the professional drivers based on averaged maximum values of lateral and longitudinal acceleration recorded during regular work. First, the recorded acceleration values of 69 city bus drivers were analysed. Then, the correlation between the acceleration values and the age and experience of the city bus drivers was examined. Based on the results of the preliminary classification of drivers, extreme values for both lateral acceleration and longitudinal acceleration (deceleration and acceleration) were obtained by 3 drivers out of the 69 tested. The study also examined the relationship between averaged values of maximum lateral and longitudinal acceleration and driver age and experience. Based on the correlation results, showed that age and the number of years of holding a driver's license are not significantly related to acceleration. Therefore, the method can be used to analyse drivers regardless of their age and experience.

Modeling and simulation of lane-changing and collision avoiding autonomous vehicles on superhighways

Collision avoidance during vehicle lane-changing was studied using modeling simulation verification method to solve the problem of collision of vehicles on superhighways. The lateral acceleration model and the collision avoidance minimum safety spacing model were established based on the theoretical analysis of the quintic polynomial lane-changing trajectory model. Additionally, the simulated minimum safety spacing of collision avoidance was calculated using vehicle speed and lane-changing time. The simulation scene was divided into general and emergency lane-changing scenarios under the condition of limiting the maximum lateral acceleration, and the simulation scenarios were subdivided into seven simulation scenarios according to different lane-changing times and road widths for simulation verification. The results demonstrated that a longer lane-changing time was selected in the general lane-changing scenario, and the lateral acceleration and swing angle speed of the vehicle decrease with the increase of the lane-changing time. This ensured collision avoidance, stable vehicle driving, and comfort and safety of passengers. The minimum safety spacing and lane-changing time were short in the emergency lane-changing scenario, and the vehicle exhibited a mild skidding phenomenon during the lane-changing. However, rollover did not occur, which ensured collision avoidance. The distances between the vehicles after the lane avoidance simulation were 4.87, 5.06, 6.89, 6.49, 7.76, 4.21, and 5.52 m, respectively. It demonstrated that the seven lane-changing and avoidance simulation models involved in this paper had good effect on vehicle collision avoidance. The effectiveness and accuracy of the steering collision avoidance of autonomous vehicles on superhighways are verified using the simulation platform, which can effectively improve the safety of superhighway driving.

Toward Hazard or Action? Effects of Directional Vibrotactile Takeover Requests on Takeover Performance in Automated Driving

The vibrotactile modality has great potential for presenting takeover requests (TORs) to get distracted drivers back into the control loop. However, few studies investigate the effectiveness of directional vibrotactile TORs. Whether TORs should be directed toward the direction of hazard (stimulus-response incompatibility) or the direction of avoidance action (stimulus-response compatibility) remains inconclusive. The present study explored the impact of directional vibrotactile TORs (toward-hazard, toward-action, and non-directional) on takeover performance. The influences of TORs lead time (3 s, 4 s, 6 s, and 8 s) and non-driving related tasks (NDRTs) (playing Tetris games and monitoring the road) on the effect of directional TORs were also probed. A total of 48 participants were recruited for our simulated driving study. Results showed that when drivers were engaged in NDRTs during automated driving, directional TORs were more effective than non-directional TORs. Specifically, at the lead times of 6 s and 8 s, both toward-hazard and toward-action TORs could shorten steering response times, compared with the non-directional TORs. At the lead times of 3 s and 4 s, toward-action TORs were more beneficial, as the maximum lateral acceleration was smaller than toward-hazard and non-directional TORs. However, when drivers monitored the road during automated driving, no obvious difference existed between directional and non-directional TORs, regardless of how long the lead time was. The findings in the present study shed light on the design and implementation of the tactile takeover system for automobile designers.