Chris Schwarz

• PhD
• Research Associate at University of Iowa

Distributed simulation technology offers enormous potential to study the interactions among road users and to assess the impact of new technologies on safety and mobility. A wide variety of studies make clear that the expectations, anticipations, and responses of drivers and non-motorized travelers to the behaviors of other road users are critical...

The National Advanced Driving Simulator is a high-fidelity motion-base simulator owned by the National Highway Transportation Safety Administration and managed and operated by the University of Iowa. Its 25-year history has intersected with some of the most significant developments in automotive history, such as advanced driver assistance systems l...

We summarize presentations from an international slate of speakers at the 2022 Automated Road Transportation Symposium on the topic of testing and data collection efforts for automated vehicles (AV), referred to throughout the chapter as automated driving systems (ADS), connected automated vehicles (CAV), cooperative driving automation (CDA), and c...

Objective: Driver monitoring systems are growing in importance as well as capability. This paper reports drowsy driving detection models that use vehicular, behavioral, and physiological data. The objectives were to augment camera-based system with vehicle-based and heart rate variability measures from a wearable device and compare the performance...

Objective: Drivers using level 2 automation are able to disengage with the dynamic driving task, but must still monitor the roadway and environment and be ready to takeover on short notice. However, people are still willing to engage with non-driving related tasks, and the ways in which people manage this tradeoff are expected to vary depending on...

This special issue, entitled “Emerging Simulation Tools and Technologies for Testing and Evaluating Connected and Automated Vehicles,” highlights several projects that either develop simulation tools or devise applications that make use of them. We hope the qualifier “emerging” adequately communicates the fast-moving and dynamic nature of ongoing w...

Intelligent traffic lights in smart cities can optimally reduce traffic congestion. In this study, we employ reinforcement learning to train the control agent of a traffic light on a simulator of urban mobility. As a difference from existing works, a policy-based deep reinforcement learning method, Proximal Policy Optimization (PPO), is utilized ra...

Digital twins found their genesis in the halls of NASA and the methods of product lifecycle management. Rapidly evolving trends around the proliferation of sensors, the internet of things, industry 4.0, and cyber-physical systems have spurred the growth of digital twins. This paper reviews digital twins and their use in connected and automated vehi...

Intelligent traffic lights in smart cities can optimally reduce traffic congestion. In this study, we employ reinforcement learning to train the control agent of a traffic light on a simulator of urban mobility. As a difference from existing works, a policy-based deep reinforcement learning method, Proximal Policy Optimization (PPO), is utilized ot...

A central question not yet examined in the literature is whether regenerative braking provides a kinematic deceleration safety advantage in time and distance over traditional service braking. Also, whether drivers This research explores three conditions of braking (traditional service braking, low level of regenerative braking, and high level of re...

From the transportation system modeling and analysis perspective, most existing simulation tools and technologies are not well suited for connected and automated vehicle (CAV) applications due to their inability to address V2X communications as well as autonomy. Calibration of the behavioral models used in traffic simulation, e.g., CAV behavior and...

Simulation offers the potential benefit of testing many miles in a variety of situations and environments. Not only can virtual testing environments be run quickly and in parallel, but a greater focus can be brought to bear on rare edge cases that need to be understood by ADS. They support simulation of sensor suites, environmental conditions, full...

Objective Understanding the factors that affect drivers’ response time in takeover from automation can help guide the design of vehicle systems to aid drivers. Higher quantiles of the response time distribution might indicate a higher risk of an unsuccessful takeover. Therefore, assessments of these systems should consider upper quantiles rather th...

A new convolutional neural network (CNN) architecture for 2D driver/passenger pose estimation and seat belt detection is proposed in this paper. The new architecture is more nimble and thus more suitable for in-vehicle monitoring tasks compared to other generic pose estimation algorithms. The new architecture, named NADS-Net, utilizes the feature p...

A new convolutional neural network (CNN) architecture for 2D driver/passenger pose estimation and seat belt detection is proposed in this paper. The new architecture is more nimble and thus more suitable for in-vehicle monitoring tasks compared to other generic pose estimation algorithms. The new architecture, named NADS-Net, utilizes the feature p...

Objective: Drowsiness is a major cause of driver impairment leading to crashes and fatalities. Research has established the ability to detect drowsiness with various kinds of sensors. We studied drowsy driving in a high-fidelity driving simulator and evaluated the ability of an automotive production-ready driver monitoring system (DMS) to detect dr...

The development of automated vehicles continues unabated. The human factor challenges of designing safe automated driving systems are critical as the first several generations of automated vehicles are expected to be semi-autonomous, requiring frequent transfers of control between the driver and vehicle. Conditional automation raises particular con...

Vehicles with partial automation, forerunners to those with higher levels of automation, are already being deployed by automakers. These current deployments, although incremental, have the potential to disrupt how people interact with vehicles. This chapter reports on a discussion of related issues that was held as part of the Human Factors Breakou...

Vehicles with SAE Level 2 or 3 automation rely on the driver to intervene and resume control when failures occur. In cases which the driver must steer upon regaining control, the initial conditions of the vehicle’s state variables can affect the success of the drivers' recovery. Hence, a model to determine the consequences of these initial states c...

As vehicle rollovers annually cause a great deal of traffic-related deaths, an increasing number of vehicles are being equipped with rollover prevention systems with the aim of avoiding such accidents. To improve the functionality of active rollover prevention systems, this study provided a potential enhanced method with the intention to predict th...

Drivers’ steering adjustments can be categorized into one-time and chain corrections. One-time corrections lead to no further steering corrections for a minimum of one second, while chain corrections have at least two consecutive steering actions. Chain corrections represent a novel indicator of steering instability. Evolving vehicle dynamics along...

Currently, buses are equipped with anti-rollover systems to prevent vehicle rollovers that cause numerous traffic deaths each year. In order to improve the functioning of the existing anti-rollover systems, this study proposes a new method to predict the lateral transfer ratio (LTR) of a bus to achieve early detection of bus rollover risks. This ea...

Over the past decade there have been significant advances in automotive headlamp technology. New illumination technologies have started to be deployed, from high intensity discharge (HID) to light emitting diodes (LED), and now Laser Phosphor illumination. In addition to new illumination technologies, adaptive headlamps have been rapidly gaining ac...

Pedal misapplications by drivers have received attention as being an underlying factor for the phenomenon known as sudden unintended acceleration (SUA) in vehicles. This research investigates behaviors during a common task for drivers, namely residential parking. Parking has been identified as a maneuver that is often linked with SUA mishaps. Using...

This study designs and evaluates a contextual and temporal algorithm for detecting drowsiness-related lane departures. The algorithm uses steering angle, pedal input, vehicle speed and acceleration as input. Speed and acceleration are used to develop a real-time measure of driving context. These measures are integrated with a Dynamic Bayesian Netwo...

Objective Driver drowsiness contributes to a substantial number of fatal and non-fatal crashes, with recent estimates attributing up to 21% of fatal crashes to drowsiness. This paper describes recent NHTSA research on in-vehicle drowsiness countermeasures. Recent advances in technology and state detection algorithms have shown success in detecting...

Driver models have been developed to capture collision-avoidance behaviors, yet there is a lack of understanding of what perceptual processes influence drivers' choices to brake or steer. A statistical model of these decisions was developed with cluster analysis and multinomial logistic regression with data from a simulator study of drivers' respon...

With the introduction of more advanced vehicle technology, it is paramount to assess its safety benefit. Advanced driver assistance systems (ADAS) can reduce crashes and mitigate crash severity, if designed appropriately. Driver behavior models are integral to the ADAS design process, complementing time and resource intensive human participant expe...

Objective: In 2012 in the United States, pedestrian injuries accounted for 3.3% of all traffic injuries but, disproportionately, pedestrian fatalities accounted for roughly 14% of traffic-related deaths (NHTSA 2014 ). In many other countries, pedestrians make up more than 50% of those injured and killed in crashes. This research project examined d...

Objective: The aim of this study was to design and evaluate an algorithm for detecting drowsiness-related lane departures by applying a random forest classifier to steering wheel angle data. Background: Although algorithms exist to detect and mitigate driver drowsiness, the high rate of false alarms and missed detection of drowsiness represent p...

Time to collision (TTC) has been a key vehicle safety metric for decades. With the increasing prevalence of advanced driver assistance systems and vehicle automation, TTC and many related metrics are being applied to the analysis of more complicated scenarios, as well as being integrated into automation algorithms. While the TTC metric was original...

Drowsy driving is a significant contributor to death and injury crashes on our Nation's highways, accounting for more than 80,000 crashes and 850 fatalities per year. The successful detection of drowsiness is a crucial step in implementing mitigation strategies to reduce the cost to society of drowsy driving. Building upon prior research in detecti...

An Electronic Stability Control (ESC) system for a vehicle is disclosed. An electronic control unit (ECU) is programmed to reduce vehicle lateral skidding by reducing differences between an intended vehicle yaw rate and an actual vehicle yaw rate by applying modifications to operation of the vehicle brakes and/or throttle. The ESC system receives i...

We are moving towards an age of autonomous vehicles. Cycles of innovation initiated in the public and private sectors have led one into another since the 1990s; and out of these efforts have sprung a variety of Advanced Driver Assistance Systems and several functioning autonomous vehicles. The challenges that face autonomous vehicle are still signi...

Drowsy driving is a significant factor in many motor vehicle crashes in the United States and across the world. Efforts to reduce these crashes have developed numerous algorithms to detect both acute and chronic drowsiness. These algorithms employ behavioral and physiological data, and have used different machine learning techniques. This work prop...

Digital maps are being linked to Advanced Driver Assistance Systems (ADAS) in numerous ways. Digital map data effectively provides a road predictive capability with a quasi-infinite range. We study the use of digital map attribute data in the enhancement of Electronic Stability Control (ESC). An offline study was conducted using real-world steering...

Limited workspace is a challenge for all motion-based simulators, whether they are large excursion systems like the National Advanced Driving Simulator or smaller simulators utilizing only Stewart Platforms. Two approaches for addressing this challenge are nonlinear washout scaling and software displacement limiting. This paper presents new algorit...

The National Advanced Driving Simulator was designed as a very high fidelity device targeted for passenger cars and trucks. The use of the NADS to simulate a different kind of vehicle would be classified as a 'non-standard' application, in light of its charter. Two recent examples of non-standard NADS applications are agricultural and construction...

The NADS models and cab for a class 8 tractor/trailer have recently been reviewed, enhanced, and implemented for a NHTSA study. A panel from the Federal Motor Carrier Safety Administration (FMCSA) reviewed the status of the NADS simulation capabilities and made several recommendations for improving its fidelity and realism. This paper is devoted to...

Recent enhancements to the NADS Image Generator necessitated the re-engineering of several of the simulator's subsystems. In addition, the visual system was also enhanced with the installation of higher resolution projectors. The vendor specifications for the projector transport delay provide numbers that are significantly lower than the old projec...

The large excursion capabilities and redundant degrees of freedom of the National Advanced Driving Simulator (NADS) motion system provide unique control and tuning challenges. The multi-belt system that drives the crossbeam and the belt that drives the turntable are both innovations in simulator technology. This paper will present some of the chara...

A virtual proving ground (VPG) was developed for use in agricultural applications using the National Advanced Driving Simulator (NADS). The VPG environment consists of a real-time tractor dynamics model, visual and terrain databases with areas suitable for various types of driving tasks, a physical tractor cab equipped with instrumented controls pr...

This paper proposes a new lattice filter structure that has the following properties. When the filter is linear time invariant (LTI), it is equivalent to the celebrated Gray-Markel lattice. When the lattice parameters vary with time, it sustains arbitrary rates of time variations without sacrificing a prescribed degree of stability, provided that t...

We consider the optimal orthonormal subband coding of zero mean cyclostationary signals, with N-periodic second order statistics. A 2-channel uniform filter bank, with N-periodic analysis and synthesis filters, is used as the subband coder. A dynamic scheme involving N-periodic bit allocation is employed. An average variance condition is used to me...

In recent years technology development for the design of electric and hybrid-electric vehicle systems has reached a peak, due to ever increasing restrictions on fuel economy and reduced vehicle emissions. An international race among car manufacturers to bring production hybrid-electric vehicles to market has generated a great deal of interest in th...

We consider the relative stability of time-invariant and time-varying unnormalized lattice filters. First, we consider a set of lattice filters whose reflection parameters α_i obey |α_i|⩽δ_i and provide necessary and sufficient conditions on the δ_i that guarantee that each time-invariant lattice in the s...

We consider a factorization scheme for linear time varying (LTV) IIR all pass systems to be used specifically in the analysis bank of multirate subband coders. The factorization scheme is based on a certain base dyadic structure. Such LTV analysis banks are required to be square systems. It is known that linear time invariant (LTI) square all pass...

We consider a multi-input, multi-output lattice realization for linear time-varying analysis banks which are all pass. Such a realization was given by Vaidyanathan and Mitra (1985) for linear time invariance (LTI) systems; and under certain conditions generalizes to the linear time varying (LTV) case. Moreover, our implementation is simpler than th...

In this paper, we consider a factorization scheme for linear time varying (LTV) IIR all pass systems to be used specifically in the analysis bank of multirate subband coders. Such LTV analysis banks are required to be square systems. It is known that linear time invariant (LTI) square all pass systems admit such dyadic factorizations and that a lim...

We consider the relative stability of time invariant and time varying unnormalized lattice filters. First, we consider a set of lattice filters whose reflection parameters α_i, obey |α_i|⩽δ_i, and provide necessary and sufficient conditions on the δ_i that guarantee that each time invariant Lattice in the...

This paper concerns the H₂-norm of plants with parametric uncertainty. For a set of continuous time plants, having denominators in intervals and numerators multiaffinely coupled to the dominators, we show that the largest H₂-norm occurs at a corner. In discrete time, corner results are presented for plants whose numerators are...

Limited workspace is a challenge for all motion-based simulators, whether they are large excursion systems, like the NADS, or smaller simulators utilizing only Stewart Platforms. Two approaches for addressing this challenge are nonlinear washout scaling and software displacement limiting. This paper presents new algorithms developed for these appro...

In order to remain on the forefront of driving simulation technology, it is necessary to continually upgrade and expand the capabilities of the NADS. One extension that is suggested by recent trends in the automotive marketplace is the ability to simulate hybrid electric vehicles. Support of hybrid electric vehicles by the NADS is motivated by the...

Truck manufacturers are introducing Roll Stability Control (RSC) and Electronic Stability Control (ESC) systems on heavy trucks including tractor-trailer type vehicles. These systems are designed to assist a driver to avoid rollovers, and in the case of ESC, yaw instability in tractor-trailers. This paper reports on the implementation of stability...