Man and his transport behaviour Part 4a. User response to price changes: application of the ‘threshold’ concept

Summary

(1) The response of an individual consumer to change in such characteristics as price will be to change behaviour at a critical point, a ‘threshold’ at which a change of behaviour is perceived to be beneficial.

(2) Most choices can be viewed as binary, for example, between pairs of transport modes. A cumulative normal distribution of responses will give an S‐shaped curve, the mid‐point being at the average threshold value.

(3) An aggregate demand curve should show the response of a given group of people to a range of price changes at one point in time. Most curves derived from revealed behaviour do not permit this. To some extent, a demand curve must be derived from interviews and other tests, giving hypothetical behaviour. Such methods are used in non‐transport consumer tests, and work by Brög et al. gives a similar picture for transport users, supporting the concept of the S‐shaped curve.

(4) Allowance for frequency of trip‐making modifies this picture, suggesting that a smoother curve may be appropriate for some conditions, such as non‐work trips. These approaches may be combined by use of catastrophe theory, with two control factors. The hysteresis effect is found around the threshold where repeated changes in the basic stimulus produce successively smaller responses.

(5) There is some evidence of symmetrical response by public transport users to real increases and reductions in cash‐paid graduated fares, but this is not the case where different forms of pricing are involved.

(6) An example of threshold effects in private transport may be found in the monitoring of tolls on the Itchen Bridge by Atkins. Demand became particularly sensitive to price in a certain range.

(7) In the public transport field, there is similar evidence from the experience of introducing flat or zonal fares where graduated fares previously applied. Where travelcards are sold, the effect is much greater, and cases such as the West Midlands show little if any effect on sales despite real price increases. Here, trips are about 7% higher than would have been expected for the same revenue target, had graduated fares been retained. However, it may well be possible to exceed the threshold, especially where fares simplification and increases are combined, as the Trondheim experience suggests.     

Comparison of inter‐city bi‐modal split models

Using data collected from rail and air passengers on two inter‐city routes in the U.K., seven different model formulations were set up and tested in order to ascertain the most appropriate model format. As a result of the work carried out, it is concluded that a simple Entropy‐type model based on the theoretical work of A. G. Wilson and utilising a linear generalised cost function is the most suitable. Other useful parameters emerging from the work are perceived values of travel time, and a weighting factor for night travel.     

Reducing the cost of peak hour transit service through contracting out service

Transit service contracting has responded to fiscal and financial woes of public transit agencies as the most uniquely attractive cost‐saving strategy at present. Most transit service contracting, however, has been in the traditional provision of entire fixed route bus service or commuter express bus service, and exclusive demand responsive service for the general public or for special disadvantaged population groups such as the elderly and/or the handicapped. This paper presents a new module in transit service contracting whereby the public and private operators jointly provide the peak service on the same route and at the same time. While the public agency provides the base demand of the service, the private provider provides the excess demand, both following the same schedules and similar service arrangements. In this paper, proposed service arrangements, costing and contracting procedures are discussed. It is also reported that substantial cost savings ranging from 32 to 57% with an average savings of 48% can be achieved if the excess peak hour bus transit service on highly peaked routes in public transit agencies is contracted to competing private operator(s).     

水泥混凝土路面结构可靠性设计方法

按现行规范的设计准则，分析水泥混凝土路面结构设计中各种不确定性因素的构成以及对设备的影响，通过引入可靠度系数建立计入各种不确定性影响的水泥混凝土路面结构可靠性设计方法。     

The wind-forced response on a buoyant coastal current: Observations of the western Gulf of Maine plume

The freshwater plume in the western Gulf of Maine is being studied as part of an interdisciplinary investigation of the physical transport of a toxic alga. A field program was conducted in the springs of 1993 and 1994 to map the spatial and temporal patterns of salinity, currents and algal toxicity. The observations suggest that the plume's cross-shore structure varies markedly as a function of fluctuations in alongshore wind forcing. Consistent with Ekman drift dynamics, upwelling favorable winds spread the plume offshore, at times widening it to over 50 km in offshore extent, while downwelling favorable winds narrow the plume width to as little as 10 km.Using a simple slab model, we find qualitative agreement between the observed variations of plume width and those predicted by Ekman theory for short time scales of integration. Near surface current meters show significant correlations between cross-shore currents and alongshore wind stress, consistent with Ekman theory. Estimates of the terms in the alongshore momentum equation calculated from moored current meter arrays also indicate a dominant Ekman balance within the plume. A significant correlation between alongshore currents and winds suggests that interfacial drag may be important, although inclusion of a Raleigh drag term does not significantly improve the alongshore momentum balance.     

基于缩尺模型的桥式抓斗卸船机应力应变特性研究

卸船机结构庞大,受力复杂,工作环境恶劣,现场试验难以组织.为减少试验成本,根据相似原理,运用量纲分析法研制了2 250 t/h桥式抓斗卸船机的相似模型,几何尺寸比例为1:40.通过模型应变检测试验,得出俯仰梁与前拉杆上5个测点在满载荷的抓斗从起升位置运动至卸料位置过程中的应力应变呈现逐渐变小的规律,实验结果与有限元分析计算结果对比基本吻合.研究结果为卸船机安全性设计和维修策略研究提供了理论依据和试验数据.     

宜昌长江公路大桥工程专项质量检验评定标准编制与研究简介

结合宜昌长江公路大桥建设实际，介绍大跨度悬索桥工程专项质量检验评定标准的编制及标准编制的技术线路、主要内容及特点。     

水泥混凝土路面接缝嵌缝料的性能

应用两弹簧一粘壶模型模拟了硅酮、聚氨酯、橡胶沥青、PVC改性沥青和聚氯乙烯胶泥嵌缝料的粘弹性性能, 给出了其粘弹性参数的回归公式, 提出了嵌缝料结构温度下降产生的拉伸应力和车辆驶过接缝引起的剪切应力计算方法, 建立了控制嵌缝料与混凝土槽壁剥落脱离的结构极限状态方程, 对所选用嵌缝料的路用性能进行了分析和评价。研究结果表明嵌缝料与混凝土槽壁的剥落脱离破坏主要由车辆驶过接缝产生的剪切应力引起的, 决定性因素是嵌缝料低温与高速剪切状态下嵌缝料的劲度, 而温度下降产生的拉伸应力的影响是次要的。     

通用信息系统开发平台研究

给出了一种通用信息系统开发平台（CISDS）的设计思想和实现方式，采用集成化开发思想对信息系统进行抽象描述和概括分析，并对通用信息系统核心数据库的结构及数据字典进行了描述，重点讨论了其使用自动化软件开发技术和软件重用技术的工作方式，阐述了各功能模块及其实现方式。