Mobile phone use by young drivers: effects on traffic speed and headways

Abstract

This paper investigates the effects of mobile phone use while driving on traffic speed and headways, with particular focus on young drivers. For this purpose, a field survey was carried out in real road traffic conditions, in which drivers' speeds and headways were measured while using or not using a mobile phone. The survey took place within a University Campus area, allowing to distinguish between settings approximating to either free flow or interrupted flow conditions. Linear and loglinear regression methods were used to investigate the effects of mobile phone use and several other young driver characteristics, such as gender, driving experience and annual distance travelled, on vehicle speeds and headways. Separate models were developed for average free flow, interrupted flow, as well as for total average speed. Results show that mobile phone use leads to a statistically significant reduction in traffic speeds of young drivers in all types of traffic conditions. Furthermore, male and female drivers reduce their speed similarly when using a mobile phone while driving. However, male drivers using their mobile phone drive at lower speeds than female drivers not using their mobile phones. Sensitivity analysis revealed that, among all explanatory variables, the effect of mobile phone use on speed was most important. Accordingly, vehicle headways appear to increase for drivers using their mobile phone. However, this effect could not be statistically validated, due to the strong correlation between speed and headway.     

沥青路面的全厚式再生暨泡沫沥青稳定(续)

泡沫沥青并不是一项新技术,早在四十多年前就已经被发现。但是直到过去一、二十年间才逐渐被人们重视而逐渐普及起来。其主要原因有以下几个方面：一是最初没有合适的设备有效而经济地提供这项技术;二是这项技术最初时属于私有专利,限制了技术的发展;第三由于近些年来对资源及环境保护的重视,人们更多地对旧有材料回收利用,从而促进了人们重新利用及开发这项技术,现在新的设备及工艺使得泡沫沥青这项技术得以更容易地实现和运用,从而在工业发达国家越来越普遍地使用。     

Multi-objective optimization of oil tanker design

Parametric optimization was applied to a double-hull AFRAMAX tanker design in order to reduce oil-outflow probability and increase cargo carrying capacity, and the results are presented here. A multi-criteria optimization procedure was set up in modeFrontier ^® using the cargo volume, the mean oil-outflow parameter and the steel weight of the cargo block as the objective functions. Calculations are based on a parametric geometric model of the ship created in NAPA ^®, and on a structural model created in POSEIDON ^®. Integration of the above software packages leads to an automated optimization procedure that provides improved feedback to the designer regarding the trade-off between the various design parameters and optimization criteria involved. The results obtained suggest notable improvements in transport capacity and oil-outflow performance for known, well-established yard designs. The presented work derives from a joint industrial project between Germanischer Lloyd (GL) and the Ship Design Laboratory of the National Technical University of Athens (NTUA-SDL), which continues the work done and coordinated by NTUA-SDL within the SAFEDOR project on the same subject.     

Which factors lead to driving errors? A structural equation model analysis through a driving simulator experiment

As driving error is a main contributory factor of road accidents, its causes and consequences are of great interest in the road safety decision making process. This paper investigates several factors (including driver distraction, driver characteristics and road environment) that affect overall driving error behaviour and estimates a new unobserved variable which underlines driving errors. This estimation is performed with data obtained from a driving simulation experiment in which 95 participants covering all ages were asked to drive under different types of distraction (no distraction, conversation with passenger, cell phone use) in rural and urban road environment, as well as in both low and high traffic conditions. Driving error was then modeled as a latent variable based on several individual driving simulator parameters. Subsequently, the impact of several risk factors such as distraction, driver characteristics as well as road environment on driving error were estimated directly. The results of this complex model reveal that the impact of driver characteristics and area type are the only statistically significant factors affecting the probability of driving errors. Interestingly, neither conversing with a passenger nor talking on the cell phone have a statistically significant impact on driving error behaviour which highlights the importance of the present analysis and more specifically the development of a measure that represents overall driving error behaviour instead of individual driving errors variables.     

Investigating the predictive performance of computational process activity-based transportation models

The aim of this paper is to achieve a better understanding of computational process activity-based models, by identifying factors that influence the predictive performance of A Learning-based Transportation Oriented Simulation System model. Therefore, the work activity process model, which includes six decision steps, is investigated. The manner of execution in the process model contains two features, activation dependency and attribute interdependence. Activation dependency branches the execution of the simulation while attribute interdependence involves the inclusion of the decision outcome of a decision step as an attribute to subsequent decision steps. The model is experimented with by running the simulation in four settings. The performance of the models is assessed at three validation levels: the classifier or decision step level, the activity pattern sequence level and the origin–destination matrix level. The results of the validation analysis reveal more understanding of the model. Benchmarks and factors affecting the predictive performance of computational activity-based models are identified.     

Classification of driver-assistance systems according to their impact on road safety and traffic efficiency

The aim was to examine driver-assistance systems that seem to have a considerable potential for road safety and traffic efficiency improvement, and to propose an impact-oriented classification of these systems. A broad overview of a series of driver-assistance systems under development or in some cases already available is presented and it identifies the basic characteristics of each system and its expected impact on traffic efficiency and road safety. The latter is assessed on the basis of appropriate evaluation criteria. Expert judgement and literature evidence available are used in this context. This impact approach, in contrast with the usually adopted user or system-oriented approaches, allows for more appropriate identification of the priorities in the field of future research, development and promotion of driver-assistance systems. The proposed classification allocates the driver-assistance systems in four different categories on the basis of whether traffic efficiency and safety impact are high or low. This categorization reveals that 40% of the systems considered are expected to have a high safety and low traffic-efficiency impact, while only 15% is expected to have both impacts high.     

Citizen Participation and Collaborative Environmental Management in the Marine Oil Trade of Coastal Alaska

This study compares the contributions to policy change made by two Regional Citizens’ Advisory Councils that participate in the environmental management of the marine oil trade in coastal regions of Alaska. Both councils are remarkably well-funded and long-enduring examples of citizen participation in environmental policy. This study finds that both councils have applied their substantial funding resources to make significant contributions to policy change (policy contributions) in the marine oil trade of coastal Alaska. This study also finds that both councils have greatly magnified their policy contributions through collaborative efforts with many other organizations active in the marine oil trade of Alaska. Therefore, the overall policy contributions of the councils result from the joint application of council resources and collaborative efforts.     

Assessing appropriate stiffness levels for spudcan foundations on dense sand

Before a jack-up can operate at a given location, a site-specific assessment of its ability to withstand a design storm during operation must be performed. During this assessment, the complex state of stress and strain under a spudcan is usually simplified to a value of foundation stiffness that is integrated as a boundary condition into the structural analysis. Soil stiffness is a critical parameter affecting the foundation and structural load distribution and displacements, and the jack-up natural period and dynamic response. The level of spudcan stiffness is an area of intense interest and debate. This paper assesses appropriate stiffness levels for numerical simulation. Utilising results from a detailed “pushover” experiment of a three-legged model jack-up on dense sand, the paper compares the experimental pushover loads and displacements on the hull and spudcans to numerical simulations using different assumptions of spudcan stiffness. These include pinned and encastré footings, linear springs and a force-resultant model based on displacement-hardening plasticity theory. Constant stiffness levels are shown to be inadequate in simulating the experimental pushover test. The non-linear degradation of stiffness associated with the latter force-resultant model is critical.