Hypothetical bias in Stated Choice Experiments: Is it a problem? And if so,how do we deal with it?

The extent to which Stated Choice (SC) experiments suffer from hypothetical bias continues to be a controversial topic in the literature. This research provides further evidence in this debate by examining the existence of hypothetical bias in a transport-related SC experiment. Data for this research were sourced from a University of Sydney study exploring the effect of exposure-based charging on motorist behaviour. The sample included 148 Sydney motorists who were recruited to take part in the 10-week GPS driving field study (Revealed Preference/RP data). In addition, participants were also required to complete an SC survey which was designed to mimic the RP decision context in order to capture what participants indicated they would do as opposed to what participants actually did in reaction to the charging regime.The current state of practice for measuring hypothetical bias in the literature is to compare aggregate differences in model outcomes using SC and RP data sources. Aggregate analysis is limited in its scope and does not allow for the calculation of the prevalence of hypothetical bias (i.e., how many participants are affected by hypothetical bias). This research is uniquely structured to allow for individual categorisation of hypothetical bias by comparing SC and RP data from the same sample for the direct purpose of investigating the prevalence of hypothetical bias. Furthermore, the extent to which mitigation techniques (cheap talk and certainty scales) influence hypothetical bias is also explored. The findings from this research show that the SC model estimates are prone to hypothetical bias and that the mitigation techniques have potential to compensate for this inherent bias.     

基于实测的桁式组合拱桥荷载偏载系数统计分析

近年来,桁式组合拱桥病害成因分析中,其活载横向偏载效应是否存在一直是工程技术人员和研究者重点研究的问题之一。结合桁式组合拱桥5座桥梁的荷载试验,利用桥梁静力荷载试验有关偏载加载工况测试数据,对桁式组合拱桥的偏载系数规律、特点进行分析和总结,相关结果可供类似桥梁设计参考。     

浅埋偏压软弱围岩双连拱隧道施工技术

研究目的:针对某市政浅埋偏压软弱围岩双连拱隧道地质软弱、围岩无自稳能力、初期支护变形大、严重偏压、易塌方的情况,总结有效性的控制变形、偏压、塌方处理的隧道施工技术,研究结果对今后类似地质条件的隧道施工有一定的借鉴作用。研究结论:(1)浅埋偏压软弱围岩双连拱隧道施工必须根据现场地质情况制定制定合理的支护参数;(2)市政地质条件差的隧道必须进行高频率的监控量测、根据数据指导施工;(3)合理地改变施工工序可以确保隧道安全顺利的贯通;(4)抗滑桩和反压回填可以有效解决软弱围岩隧道偏压问题。     

大跨黄土隧道下穿公路施工技术

在上新庄隧道出口下穿既有公路施工中,根据隧道出口位置和地质情况,优化了隧道进洞方案和洞内施工方法,同时调整了初期支护参数,有效地控制了黄土隧道沉降和变形,降低了施工成本,同时也积累了黄土隧道下穿既有公路的施工经验。     

浅埋小净距偏压隧道合理开挖顺序探讨

运用ANSYS有限元程序,研究浅埋偏压小净距隧道在不同的偏压角度、间距、埋深条件下,先开挖深埋侧和先开挖浅埋侧2种不同的开挖顺序下的受力和变形特性,对比分析了围岩最大拉应力、围岩洞周最大位移、中岩柱水平位移和竖向应力。研究结果表明：随着角度的增加,先开挖深埋侧较先开挖浅埋侧隧道及中岩柱更加安全;当间距小于0．5倍洞径时,先开挖深埋侧较先开挖浅埋侧安全;当间距大于0．75倍洞径时,先开挖浅埋侧对于隧道受力更加有利;当埋深在1倍洞径以下,先开挖深埋侧隧道整体稳定性及受力更加安全,当埋深大于1．5倍洞径时,先开挖浅埋侧隧道受力更加安全。     

基于目标拓扑参照图的雷达航迹抗差关联方法

针对雷达系统偏差影响下数据关联容易错误的问题,提出一种基于目标拓扑参照图的数据抗差关联新方法,该方法首先将目标进行聚类减少关联复杂度,再对聚类目标拓扑参照图经过平移、旋转和尺度等变换进行关联匹配,达到目标关联一致性的目的。仿真结果表明了该方法具有较高的关联精度和鲁棒性。     

Investigating the nature and impact of reporting bias in road crash data

This paper investigates the nature, and impact of the reporting bias associated with the police-reported crash data on inferences made using this data. In doing so, we merge a detailed emergency room data and police-reported crash data for a specific region in Denmark. To disentangle potentially common observable and unobservable factors that affect drivers’ injury severity risk and their crash reporting behavior, we formulate a bivariate ordered-response probit model of injury severity risk and crash reporting propensity. To empirically identify the reporting bias in this joint model, we exploit an exogenous police reform that particularly affects some specific municipalities of the region under consideration. The empirical analysis reveals substantial reporting bias in the commonly used police-reported road crash data. This non-random sample selection associated with the police-reported crash data leads to biased estimates on the effect of some of the explanatory variables in injury severity analysis. For instance, estimates based on the police-reported crash data substantially underestimate the effectiveness of seat belt use in reducing drivers’ injury severity risk.     

列车运行工况对电力变压器直流偏磁影响的仿真分析

地铁中存在的杂散电流会对地表电位分布产生影响,而如果周边存在电力变压器时,变压器中流过的直流电流会造成变压器发生直流偏磁,然而,目前关于地铁地表电位分布对周边变压器直流偏磁影响研究较少,为此考虑了列车上下行4种不同运行状况,搭建地铁地表电位仿真模型,并计算相应情况下变压器励磁电流畸变率,得出上下行列车同时出站时,对变压...     

铁路车辆25kV电压互感器直流偏磁性能试验研究

针对我国电气化铁路机车和动车组25 kV电压互感器过热烧损情况,设计了可对25 kV电压互感器进行直流偏磁性能试验的方法。通过对国产和进口型号25 kV电压互感器直流偏磁性能试验,获得了它们的抗直流偏磁性能数据。理论分析和现场测量表明,接触网最高可能发生4 kV直流偏磁电压,按统计学计算,产品的抗直流偏磁水平应达到2.5 kV,而目前多数产品的抗直流偏磁水平一般只能达到1.5 kV,这是造成25 kV电压互感器运行中过热烧损的主要原因。因此,在产品的标准化设计中应重点考虑抗直流偏磁的参数大小。通过试验对比可知,采用部分磁路气隙设计的产品比采用降低额定工作磁密设计的产品有更好的抗直流偏磁性能,可以满足抗直流偏磁水平2.5 kV的要求。     

地层倾角对浅埋偏压隧道拱顶沉降的影响研究

借助FLAC~(3D)有限差分软件,着重考虑地层倾角,结合现场量测,对重庆黔江蒲草沟Ⅴ级浅埋偏压隧道进行结构稳定性分析,探讨不同地层倾角下隧道的拱顶沉降特征。研究表明:所构建的数值模型对拱顶沉降的预测值与现场实测值变形规律基本吻合,且最大差值仅为0.87 mm,验证了本次数值模拟的正确性;随着砾岩夹砂岩层倾角增大,拱顶沉降呈加速增大趋势,开挖面处拱顶沉降变化率也显著提高;砾岩夹砂岩层倾角与地形一致导致的误差为16.4%,倾角为水平导致的误差为11.9%,误差均较大。由此可知,在砾岩夹砂岩层倾角变大的情况下,应提高隧道结构的强度,在数值计算中简化地层倾角会导致较大的计算误差。研究成果可推广应用于砾岩夹砂岩层的浅埋偏压隧道。