Estimation of origin-destination matrices from link counts and sporadic routing data

Estimation of origin-destination (OD) matrices from link count data is a challenging problem because of the highly indeterminate relationship between the observations and the latent route flows. Conversely, estimation is straightforward if we observe the path taken by each vehicle. We consider an intermediate problem of increasing practical importance, in which link count data is supplemented by routing information for a fraction of vehicles on the network. We develop a statistical model for these combined data sources and derive some tractable normal approximations thereof. We examine likelihood-based inference for these normal models under the assumption that the probability of vehicle tracking is known. We show that the likelihood theory can be non-standard because of boundary effects, and provide conditions under which such irregular behaviour will be observed in practice. For regular cases we outline connections with existing generalised least squares methods. We then consider estimation of OD matrices under estimated and/or misspecified models for the probability of vehicle tracking. Theoretical developments are complemented by simulation experiments and an illustrative example using a section of road network from the English city of Leicester.     

Recursive estimation of average vehicle time headway using single inductive loop detector data

Vehicle time headway is an important traffic parameter. It affects roadway safety, capacity, and level of service. Single inductive loop detectors are widely deployed in road networks, supplying a wealth of information on the current status of traffic flow. In this paper, we perform Bayesian analysis to online estimate average vehicle time headway using the data collected from a single inductive loop detector. We consider three different scenarios, i.e. light, congested, and disturbed traffic conditions, and have developed a set of unified recursive estimation equations that can be applied to all three scenarios. The computational overhead of updating the estimate is kept to a minimum. The developed recursive method provides an efficient way for the online monitoring of roadway safety and level of service. The method is illustrated using a simulation study and real traffic data.     

Identifying optimal data aggregation interval sizes for link and corridor travel time estimation and forecasting

With the recent increase in the deployment of ITS technologies in urban areas throughout the world, traffic management centers have the ability to obtain and archive large amounts of data on the traffic system. These data can be used to estimate current conditions and predict future conditions on the roadway network. A general solution methodology for identifying the optimal aggregation interval sizes for four scenarios is proposed in this article: (1) link travel time estimation, (2) corridor/route travel time estimation, (3) link travel time forecasting, and (4) corridor/route travel time forecasting. The methodology explicitly considers traffic dynamics and frequency of observations. A formulation based on mean square error (MSE) is developed for each of the scenarios and interpreted from a traffic flow perspective. The methodology for estimating the optimal aggregation size is based on (1) the tradeoff between the estimated mean square error of prediction and the variance of the predictor, (2) the differences between estimation and forecasting, and (3) the direct consideration of the correlation between link travel time for corridor/route estimation and forecasting. The proposed methods are demonstrated using travel time data from Houston, Texas, that were collected as part of the automatic vehicle identification (AVI) system of the Houston Transtar system. It was found that the optimal aggregation size is a function of the application and traffic condition.

强度折减法在平面滑动型岩质边坡的应用*

岩质边坡平面滑动验算包括岩体内部结构面验算和岩体抗剪强度验算.均质边坡岩体由于抗剪不足产生平面滑动,通过假定破坏面与内摩擦角之间关系迭代求解安全系数,探寻破裂角和内摩擦角之间的关系,进而提出简化估算安全系数公式.通过与数值解对比验算,可知简化公式精度能够满足工程设计要求,可为实际工程提供参考和借鉴.     

空气层结对港口细煤粉污染扩散的影响分析

通过分析空气层结对港口细煤粉扩散的影响,得出离源0.5 km处稳定层结、中性层结及不稳定层结3种层结条件下污染物的浓度峰值分别为1.3 mg/m',0.27 mg/m'和0.02 mgW,同时得出5.5 m/s,7 m/s两种风速条件下的污染物浓度峰值.结果表明,湍流处于不稳定层结时,浓度分布峰值相对较小;随着层结逐渐...     

考虑电动自行车骑行的非机动车道最大纵坡探讨

现行规范要求非机动车道的最大纵坡不超过3.5%,但要在山地城市、跨江桥梁两岸慢行系统衔接等场景下满足该要求存在工程占地大、造价高、可实施性差等问题,考虑到电动自行车在非机动车出行方式中占比越来越高的实际情况,以《电动自行车安全技术规范》（GB 17761—2018）规定的国标电动自行车为研究对象对骑行过程进行受力分析,提出了可满足电动自行车骑行要求的非机动车道最大纵坡参考值,可供电动车骑行占比高的类似项目参考。     

风积沙的工程力学性质试验研究

结合毛乌素沙漠沙样,对风积沙的工程力学性质进行了系统的试验研究。试验结果表明:风积沙的压实可采用常规的击实试验方法和振动密实法,压实效果受颗粒级配、含水量、荷载大小、振动频率及振幅等多种因素影响;风积沙的内摩擦角与压实度之间呈线性变化规律,颗粒级配是主要影响因素,含水量影响较小;风积沙的室内回弹模量和加州承载比与压实度之间大致呈非线性增大规律,在某一压实度区间增大的幅度非常小。     

Quasi-dynamic estimation of o–d flows from traffic counts: Formulation,statistical validation and performance analysis on real data

The paper proposes a “quasi-dynamic” framework for estimation of origin–destination (o–d) flow from traffic counts, under the assumption that o–d shares are constant across a reference period, whilst total flows leaving each origin vary for each sub-period within the reference period. The advantage of this approach over conventional within-day dynamic estimators is that of reducing drastically the number of unknowns given the same set of observed time-varying traffic counts. Obviously, the gain in accuracy depends on how realistic is the underlying assumption that total demand levels vary more rapidly over time than o–d shares. Firstly, the paper proposes a theoretical specification of the quasi-dynamic estimator. Subsequently, it proposes empirical and statistical tests to check the quasi-dynamic assumption and then compares the performances of the quasi-dynamic estimator of o–d flows with both classical off-line simultaneous dynamic estimators and on-line recursive Kalman filter-based estimators. Experiments are carried out on the real test site of A4–A23 motorways in North-Eastern Italy. Results confirm the acceptability of the assumption of quasi-dynamic o–d flows, even under the hypothesis of constant distribution shares for the whole day and show that the quasi-dynamic estimator outperforms significantly the simultaneous estimator. Data also suggest that using the quasi-dynamic estimates instead of the simultaneous estimates as historical o–d flows improves significantly the performances of the Kalman filter, which strongly depends of the quality of the seed o–d flows. In addition, it is shown that the aggregation of quasi-dynamic o–d estimates across subsequent time slices represents also the most effective way to obtain o–d estimates for larger time horizons (e.g. hourly estimates). Finally, a validation based on an hold-out sample of link flows (i.e. counts not used as inputs in the o–d estimation/updating process) revealed the quasi-dynamic estimator to be overall more robust and effective with respect to the other tested estimators.     

应用广义最大覆盖模型进行公路养护应急中心布局选址研究

应用广义最大覆盖模型方法在江西省国省道公路网络中进行公路养护应急中心布局选址,将养护应急中心设置在县级及以上行政中心点上,在点的服务半径已知的条件下,求解如何设立数量最少的点便可覆盖所有区域.     

浅谈公路工程估算编制的新规则

新的《公路工程基本建设项目投资估算编制办法》和《公路工程估算指标》自2012年1月1日正式实施。取代1996编办和指标,针对估算编制的新规则,分析总结新旧差异,为以后估算编制工作提供指导。