Understanding the role of the forecast-maker in overestimation forecasts of policy impacts: The case of Travel Demand Management policies

Forecasting the impacts of a proposed policy is an important component of the transportation planning and decision making process. Although scientific tools are often used in transportation forecasts, biases and, more specifically, overestimations of the expected impact are often observed. This study explores the correlations between forecast-maker’s characteristics and forecast bias creation and reduction. The study examines two transport-related policies aiming at the reduction of car use: telecommuting and carsharing. Both are Travel Demand Management (TDM) policies, which attract much attention from transport experts. We tested the extent to which the forecast-maker’s beliefs about the policy at stake affected the forecast bias. We found that attitudes and beliefs associates not only with overestimation bias but also with its reduction over time. We also tested the extent to which the forecast-maker’s affiliation, the performing institute and the publication type were correlated with the biases of the forecast and with the forecaster attitudes and beliefs. These characteristics are intuitively used by the forecast user as tools to assess the ‘objectivity’ of the forecast, but our analysis found no association between these characteristics and the forecast bias.     

水泥搅拌桩水泥土强度特性试验研究

文章通过对某沿海高速公路的软土地基进行水泥搅拌桩固化试验,测试其桩体水泥土的重度和无侧限抗压强度,分析水泥搅拌桩强度的影响因素,统计得到了以14 d和28 d强度预测90 d强度的公式。研究结果表明:水泥土重度比未加固前约增加1.6%~6.1%,水泥土强度随固化龄期和水泥掺量的增长而增大,随土体含水量的增大而降低。     

灰色理论在高速公路软土地基沉降预测中的应用

运用灰色理论对高速公路软土地基沉降进行预测,建立不等时距的预测模型GM(1,1),采用后验差法对模型的可靠性进行检验,弥补等时距GM(1,1)模型的不足。同时,结合沿江高速公路常州段实测数据,进行计算机模拟,得出了预测模型,并与实测结果进行对比和分析,结果理想可靠,证明了该法的实用性。