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Northwestern University

Human Performance in Transportation Safety


Mobility Trends and COVID-19 in the City of Chicago

Researcher(s): Hani S. Mahmassani, Divyakant Tahlyan
Year: 2020 (ongoing)

CHICAGO — The Northwestern University Transportation Center is tracking crash data in Chicago during the COVID-19 pandemic. Its latest analysis has found that while there have been fewer crashes overall, there is a slight increase in the severity of the crashes. 

During the first week of March, Chicago saw 2,063 reported crashes. That number began dropping after March 13, when the federal government declared a national emergency and dropped further after Illinois’ Stay At Home order began on March 21st.  Last week, Chicago was down to 803 crashes.  

Source: WGN News


Anomalous Diffusion and the Structure of Human Transportation Networks

Researcher(s): Dirk Brockmann
Year: 2008

The dispersal of individuals of a species is the key driving force of various spatiotemporal phenomena which occur on geographical scales. It can synchronise populations of interacting species, stabilise them, and diversify gene pools [1–3]. The geographic spread of human infectious diseases such as influenza, measles and the recent severe acute respiratory syndrome (SARS) is essentially promoted by human travel which occurs on many length scales and is sustained by a variety of means of transportation [4–8]. In the light of increasing international trade, intensified human traffic, and an imminent influenza A pandemic the knowledge of dynamical and statistical properties of human dispersal is of fundamental importance and acute [7,9,10]. A quantitative statistical theory for human travel and concomitant reliable forecasts would substantially improve and extend existing prevention strategies. Despite its crucial role, a quantitative assessment of human dispersal remains elusive and the opinion that humans disperse diffusively still prevails in many models [11]. In this chapter I will report on a recently developed technique which permits a solid and quantitative assessment of human dispersal on geographical scales [12]. The key idea is to infer the statistical properties of human travel by analysing the geographic circulation of individual bank notes for which comprehensive datasets are collected at the online bill-tracking website The analysis shows that the distribution of travelling distances decays as a power law, indicating that the movement of bank notes is reminiscent of superdiffusive, scale free random walks known as L`evy flights [13]. Secondly, the probability of remaining in a small, spatially confined region for a time T is dominated by heavy tails which attenuate superdiffusive dispersal. I will show that the dispersal of bank notes can be described on many spatiotemporal scales by a two parameter continuous time random walk (CTRW) model to a surprising accuracy. To this end, I will provide a brief introduction to continuous time random walk theory [14] and will show that human dispersal is an ambivalent, effectively superdiffusive process.

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Chasing the Silver Bullet: Measuring Driver Fatigue Using Simple and Complex Tasks

Researcher(s): S. Baulk, S. Biggs, K.J. Reid, C. van den Heuvel, D. Dawson
Year: 2008

Driver fatigue remains a significant cause of motor-vehicle accidents worldwide. New technologies are increasingly utilised to improve road safety, but there are no effective on-road measures for fatigue. While simulated driving tasks are sensitive, and simple performance tasks have been used in industrial fatigue management systems (FMS) to quantify risk, little is known about the relationship between such measures. Establishing a simple, on-road measure of fatigue, as a fitness-to-drive tool, is an important issue for road safety and accident prevention, particularly as many fatigue related accidents are preventable. This study aimed to measure fatigue-related performance decrements using a simple task (reaction time – RT) and a complex task (driving simulation), and to determine the potential for a link between such measures, thus improving FMS success. Fifteen volunteer participants (7 m, 8 f) aged 22–56 years (mean 33.6 years), underwent 26 h of supervised wakefulness before an 8 h recovery sleep opportunity. Participants were tested using a 30-min interactive driving simulation test, bracketed by a 10-min psychomotor vigilance task (PVT) at 4, 8, 18 and 24 h of wakefulness, and following recovery sleep. Extended wakefulness caused significant decrements in PVT and driving performance. Although these measures are clearly linked, our analyses suggest that driving simulation cannot be replaced by a simple PVT. Further research is needed to closely examine links between performance measures, and to facilitate accurate management of fitness to drive, which requires more complex assessments of performance than RT alone.

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Effectiveness of Innovative Speed Enforcement Techniques in Illinois

Researcher(s): Hani Mahmassani, Pei-Wei Lin
Year: 2009

Speed is a contributory factor in 29% of traffic-related fatal crashes occurring on Illinois highways. The Federal Highway Administration has identified Illinois as a Speed Focus State and has encouraged Illinois to develop a speed management program. Efforts have been made to address speed related fatalities and serious injuries on Illinois highways. In an era of a struggling economy, reducing resources, and competing needs, leaders within the public and private sector are turning to intelligence-driven assignments to produce the greatest gain with the least amount of investment. Once analyzed it is believed this information will provide the intelligence needs to develop more effective patrol strategies and procedures with the least amount of people.

This study attempts to identify the most effective speed enforcement patrol and saturation patrol procedures and methods, including effective enforcement duration and appropriate staffing level needs in order to more efficiently deploy valuable resources and maximize results. The results from this study will ultimately assist in the efforts to reduce speed-related traffic fatalities and serious injuries occurring on Illinois highways.

The analyses will results in a better understanding of the presence/absence and duration of speed enforcement on Illinois highways. Best practices for patrol and saturation patrol procedures will be provided from the research. In addition, there should be a better understanding of how the reduction of speed correlates to the reduction of severe crashes. The findings will allow IDOT and ISP to better allocate resources and ultimately reduce speed-related fatalities on Illinois highways.

Human Mobility and Spatial Disease Dynamics

Researcher(s): Dirk Brockmann, Vincent David, Alejandro Morales Gallardo
Year: 2009

The understanding of human mobility and the development of qualitative models as well as quantitative theories for it is of key importance to the research of human infectious disease dynamics on large geographical scales. In our globalized world, mobility and traffic have reached a complexity and volume of unprecedented degree. Long range human mobility is now responsible for the rapid geographical spread of emergent infectious diseases. Multiscale human mobility networks exhibit two prominent features: (1) Networks exhibit a strong heterogeneity, the distribution of weights, traffic fluxes and populations sizes of communities range over many orders of magnitude. (2) Although the interaction magnitude in terms of traffic intensities decreases with distance, the observed power-laws indicate that long range interactions play a significant role in spatial disease dynamics. We will review how the topological features of traffic networks can be incorporated in models for disease dynamics and show, that the way topology is translated into dynamics can have a profound impact on the overall disease dynamics. We will also introduce a class of spatially extended models in which the impact and interplay of both spatial heterogeneity as well as long range spatial interactions can be investigated in a systematic fashion. Our analysis of multiscale human mobility networks is based on a proxy network of dispersing US dollar bills, which we incorporated in a model to produce real-time epidemic forecasts that projected the spatial spread of the recent outbreak of Influenza A(H1N1).

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Clearview Font in Traffic Signs: Assessing IDOT Experiences and Needs

Researcher(s): Hani Mahmassani, Pei-Wei Lin
Year: 2010

This study will determine i) the extent to which the Clearview font is presently used in Illinois; ii) the issues involved with converting existing signs to Clearview font; and iii) the positive impacts on motorist guidance and safety from shifting to Clearview font. For example, using the font could impact the dimensions of the signs used, if Clearview requires a higher or longer character height and width to provide the same level of recognition and legibility, and consequently safety. As such, the study will help identify the needs of IDOT in relation to using the Clearview font.

The primary objective of the study is to evaluate the current state of practice for traffic signage on Illinois highways with regard to the use of the Clearview font, and to better understand driver responses to and experience with the Clearview font in different locations and across different trip purposed, in actual everyday traffic.

Modeling Human Behavior and Intelligent Agent-Based Traffic Flow Simulation

Researcher(s): Hani Mahmassani
Year: 2007

This three year study, funded by the National Science Foundation, put forward a comprehensive, multidisciplinary research approach to characterize and model human cognitive driving behavior and subsequent response in traffic flow systems. Specifically, the dynamics of driver behavior, taken at the individual level and as part of a group, evolving over time and space will be systematically studies as a complex system. By developing behavior-based models of human decision-making in traffic situations and integrating the behavior models in computer simulation systems, the study addresses fundamental questions in traffic science and promises to improve prevailing understanding of traffic flow phenomena as well as the fidelity and reliability of the current state of the art of traffic flow simulation. Of particular interest in this study is driving behavior under extreme conditions, including inclement weather, natural and man-made disasters.

Perception of Simulated Driving Performances After Sleep Restriction and Caffeine

Researcher(s): SN Biggs, A. Smith J. Dorrian, K. Reid, D. Dawson, C. van den Heuvel, S. Baulk S.
Year: 2007

Objective: As feelings of alertness are reported to be highly correlated with performance perception, the objective of this study was to determine whether caffeine, a common countermeasure to driver sleepiness, affected a sleepy driver's ability to monitor his or her simulated driving performance.
Methods: Twelve healthy young adults (six males, six females) participated in three counterbalanced, blinded, daytime conditions: control [9 h time in bed (TIB)], 100 mg caffeine (4 h TIB), and placebo (4 h TIB). Driving performance was measured through lane drift on a series of 30-min simulated driving sessions. Subjective sleepiness and perception of driving performance were measured at 5-min intervals during driving sessions via the Karolinska Sleepiness Scale and a corresponding perception scale.
Results: Sleep restriction had a significant detrimental effect on driving performance and subjective measures. Caffeine resulted in significant improvements across all measures. Subjective measures were found to be significantly correlated after sleep restriction and prior to caffeine. Correlations between actual and perceived performance were nonsignificant across all conditions.
Conclusions: The strong correlation between subjective measures supports the postulation that sleepiness is used as a cue for performance prediction when sleep restricted. The relationship between perceived and actual performance after fatigue countermeasures remains inconclusive. Further research, addressing limitations, is needed.

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The Relationship Between the Rate of Melatonin Excretion and Sleep Consolidation for Locomotive Engineers in Natural Sleep Settings

Researcher(s): Gregory D Roach, Kathryn J Reid, Sally Ferguson, Drew Dawson
Year: 2006

Background: The aim of the study was to examine the role that melatonin production plays in the regulation of sleep consolidation in a population of shiftworkers working and sleeping in their natural environments.

Methods: 253 locomotive engineers (249 male, 4 female, mean age = 39.7 years) participated in the study for a 2-week period whilst working their normal roster patterns. Participants recorded details for all sleep periods in a sleep diary and collected urine samples during each day's main sleep period. The samples were subsequently assayed for the metabolite of melatonin in urine, 6-sulphatoxymelatonin (aMT6s), and the rate of excretion during main sleep periods was calculated.

Results: Separate one-way factorial ANOVAs revealed a significant effect of time of sleep onset on aMT6s excretion rate, sleep duration, and subjective sleep quality. Generally, the rate of aMT6s excretion was lower, sleep duration was shorter, and sleep quality was lower for sleeps initiated during the daytime than for sleeps initiated at night.

Conclusion: Combined with previous studies linking melatonin production and sleep propensity, and others demonstrating the relationship between sleep consolidation and melatonin production in forced desynchrony protocols, the current results indicate that low production of melatonin may play a role in the poor consolidation of daytime sleep in natural sleep settings.

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