Hubris or humility? Accuracy issues for the next 50 years of travel demand modeling

This study reviews the 50-year history of travel demand forecasting models, concentrating on their accuracy and relevance for public decision-making. Only a few studies of model accuracy have been performed, but they find that the likely inaccuracy in the 20-year forecast of major road projects is ±30 % at minimum, with some estimates as high as ±40–50 % over even shorter time horizons. There is a significant tendency to over-estimate traffic and underestimate costs, particularly for toll roads. Forecasts of transit costs and ridership are even more uncertain and also significantly optimistic. The greatest knowledge gap in US travel demand modeling is the unknown accuracy of US urban road traffic forecasts. Modeling weaknesses leading to these problems (non-behavioral content, inaccuracy of inputs and key assumptions, policy insensitivity, and excessive complexity) are identified. In addition, the institutional and political environments that encourage optimism bias and low risk assessment in forecasts are also reviewed. Major institutional factors, particularly low local funding matches and competitive grants, confound scenario modeling efforts and dampen the hope that technical modeling improvements alone can improve forecasting accuracy. The fundamental problems are not technical but institutional: high non-local funding shares for large projects warp local perceptions of project benefit versus costs, leading to both input errors and political pressure to fund projects. To deal with these issues, the paper outlines two different approaches. The first, termed ‘hubris’, proposes a multi-decade effort to substantially improve model forecasting accuracy over time by monitoring performance and improving data, methods and understanding of travel, but also by deliberately modifying the institutional arrangements that lead to optimism bias. The second, termed ‘humility’, proposes to openly quantify and recognize the inherent uncertainty in travel demand forecasts and deliberately reduce their influence on project decision-making. However to be successful either approach would require monitoring and reporting accuracy, standards for modeling and forecasting, greater model transparency, educational initiatives, coordinated research, strengthened ethics and reduction of non-local funding ratios so that localities have more at stake.     

The visual impact of development in coastal zone areas

Abstract

The focus of this paper is theoretical, as well as methodological. It reviews previous studies of visual impact and reports research by the author on people's evaluation of the appropriateness of different man‐made facilities in different coastal‐area contexts and other environments. In this study, subjects were asked to react to slides developed through the use of landscape models and experimental facilities to simulate the appearance of a building in the landscape, while systematically varying the visual relatedness between the two. Specific interest centered on the variable of congruity vs. contrast between the appearance of the building and its landscape context, manipulated by co‐varying the attributes of color and size to create a five‐point scale of contrast/obtrusiveness. The hypothesis was that judgments of appropriateness, and to a lesser extent judgments of liking, would vary inversely with level of contrast. The role of two further variables, the functional significance of the building in its setting, and the character of the setting itself, was also investigated. The author reviews methodological issues involved where subjects respond to visual stimuli for purposes of judging change in visual quality. These methodological issues include: stimulus‐selection and problems of simulation, choice of response measures, and choice of respondents, and the treatment of individual differences. The author calls for development of standardized scales and indices such as “perceptually‐relevant environmental quality indicators.”     

Motorway signals and the detection of incidents

A mathematical model of automobile trip tours is presented. Within a framework of eight common restrictions on automobile trip making, all travel behavior is assumed random and all of the ways in which tours can be arranged are assumed equally likely. Three probability distributions are derived from the model: (1) the probability that a household makes a given number of tours in a day; (2) the probability that a household makes a given number of trips in a day; and (3) the probability that a tour reaches a given number of destinations. It is shown that the model agrees with similar probability distributions generated from home‐interview data for Milwaukee.     

The dredging dilemma: Economic development and environmental protection in Oakland Harbor

Abstract

Seaport expansion often generates tensions between the national interest in efficient transport and local interests in water quality and habitat preservation. The governing American permitting system, however, establishes an extraordinarily cumbersome, legalistic, and costly method for balancing environmental and economic considerations. A case study of the Port of Oakland illustrates the tendency. For four years, plans to find an environmentally acceptable site for dredged material have been stymied by a sequence of inconclusive regulatory and judicial proceedings. Meanwhile, large container ships can enter and leave Oakland harbor only at high tide, and not fully loaded. Despite the absence of any authoritative determination concerning environmental risks, the port was compelled to accede to progressively more expensive disposal methods. Such “adversarial legalism”; is not unique to the Oakland harbor case, but recurs in other policy spheres. It stems from a governmental structure that fragments decision‐making power among many agencies, that constrains regulatory discretion with legal demands for scientific certainty, and that by allowing agency decisions to be challenged readily in court, encourages legalistic defensiveness and extortion rather than compromise. The article concludes with a discussion of the conditions under which regional planning bodies might overcome these centrifugal tendencies.     

新型公共交通外部电源供电模式分析

对适用于新型公共交通的外部电源供电模式优缺点及适用范围进行了分析.提出了一种基于单电源、单环网的新的供电模式.经综合比较分析,新的供电模式具有较好的经济性和可实施性.在具体工程中,应根据沿线的外部电源情况、本线的牵引和动力照明负荷的分布和大小,以及供电安全和可靠性的要求,选择最合理的供电方式.     

Haptic steering support for driving near the vehicle’s handling limits; skid-pad case

Current vehicle dynamic control systems from simple yaw control to high-end active steering support systems are designed to primarily actuate on the vehicle itself, rather than stimulate the driver to adapt his/her inputs for better vehicle control. The driver though dictates the vehicle’s motion, and centralizing him/her in the control loop is hypothesized to promote safety and driving pleasure. Exploring the above statement, the goal of this study is to develop and evaluate a haptic steering support when driving near the vehicle’s handling limits (Haptic Support Near the Limits; HSNL). The support aims to promote the driver’s perception of the vehicle’s behaviour and handling capacity (the vehicle’s internal model) by providing haptic (torque) cues on the steering wheel. The HSNL has been evaluated in (a) driving simulator tests and (b) tests with a vehicle (Opel Astra G/B) equipped with a variable steering feedback torque system. Drivers attempted to achieve maximum velocity while trying to retain control in a circular skid-pad. In the simulator (a) 25 subjects drove a vehicle model parameterised as the Astra on a dry skid-pad while in (b) 17 subjects drove the real Astra on a wet skid-pad. Both the driving simulator and the real vehicle tests led to the conclusion that the HSNL assisted subjects to drive closer to the designated path while achieving effectively the same speed. With the HSNL the drivers operated the tires in smaller slip angles and hence avoided saturation of the front wheels’ lateral forces and excessive understeer. Finally, the HSNL reduced their mental and physical demand.     

Road Traffic Demand Elasticity Estimates: A Review

A brief summary of road traffic‐related elasticity estimates as reported in the international literature is given. An indication of the orders of magnitude of these elasticities is outlined and the variation in estimates commonly found is emphasized. The results of previous extensive surveys are collated, but a wider scope of traffic‐related research is provided by reviewing recent work and including research that has received less attention. A variety of elasticity measures related to car travel, car ownership, freight traffic and fuel demand are reported. Based on the review, some important themes underpinning the demand for road traffic are revealed.     

“火长”辨正

火长是航海罗盘发明之后对掌握航海罗盘这一工具的专职人员的称谓,始于南宋中叶航海罗盘的成熟期。火长称谓的源起是航海罗盘脱胎于堪舆罗盘的缘故,与我国堪舆学说中的五行阴阳八卦理论有关。火长在海船上至少有一正一副的配备,还可按航行海区的情况配备多达8人的火长。火长不但向外传播导航技术,同时也通过聘请番火长学习天文导航技术。火长堪称航海文化中的一朵奇葩。