Accuracy of the Gothenburg congestion charges forecast

This paper explores the accuracy of the transport model forecast of the Gothenburg congestion charges, implemented in 2013. The design of the charging system implies that the path disutility cannot be computed as a sum of link attributes. The route choice model is therefore implemented as a hierarchical algorithm, applying a continuous value of travel time (VTT) distribution. The VTT distribution was estimated from stated choice (SC) data. However, based on experience of impact forecasting with a similar model and of impact outcome of congestion charges in Stockholm, the estimated VTT distribution had to be stretched to the right. We find that the forecast traffic reductions across the cordon and travel time gains were close to those observed in the peak. However, the reduction in traffic across the cordon was underpredicted off-peak. The necessity to make the adjustment indicates that the VTT inferred from SC data does not reveal the travellers’ preferences, or that there are factors determining route choice other than those included in the model: travel distance, travel time and congestion charge.     

牵引车-半挂车列车动力学仿真研究

在合理的理论假设基础上建立了较为精细的牵引车-半挂车的整车动力学仿真模型。应用此模型,针对6×4牵引车拖挂2轴半挂车列车的折叠、甩尾、倾翻及转向瞬态响应进行了仿真,并对各工况的特点进行了分析。仿真结果表明该模型能够很好地模拟车辆在各种危险工况下的运动状态,从而为进一步研究牵引车-半挂车列车的性能特点提供了很好的工具。     

Validation of traffic flow models with respect to the spatiotemporal evolution of congested traffic patterns

We propose a quantitative approach for calibrating and validating key features of traffic instabilities based on speed time series obtained from aggregated data of a series of neighboring stationary detectors. The approach can be used to validate models that are calibrated by other criteria with respect to their collective dynamics. We apply the proposed criteria to historic traffic databases of several freeways in Germany containing about 400 occurrences of congestions thereby providing a reference for model calibration and quality assessment with respect to the spatiotemporal dynamics. First tests with microscopic and macroscopic models indicate that the criteria are both robust and discriminative, i.e., clearly distinguishes between models of higher and lower predictive power.     

Trajectory data reconstruction and simulation-based validation against macroscopic traffic patterns

This paper shows that the behavior of driver models, either individually or entangled in stochastic traffic simulation, is affected by the accuracy of empirical vehicle trajectories. To this aim, a “traffic-informed” methodology is proposed to restore physical and platoon integrity of trajectories in a finite time–space domain, and it is applied to one NGSIM I80 dataset. However, as the actual trajectories are unknown, it is not possible to verify directly whether the reconstructed trajectories are really “nearer” to the actual unknowns than the original measurements. Therefore, a simulation-based validation framework is proposed, that is also able to verify indirectly the efficacy of the reconstruction methodology. The framework exploits the main feature of NGSIM-like data that is the concurrent view of individual driving behaviors and emerging macroscopic traffic patterns. It allows showing that, at the scale of individual models, the accuracy of trajectories affects the distribution and the correlation structure of lane-changing model parameters (i.e. drivers heterogeneity), while it has very little impact on car-following calibration. At the scale of traffic simulation, when models interact in trace-driven simulation of the I80 scenario (multi-lane heterogeneous traffic), their ability to reproduce the observed macroscopic congested patterns is sensibly higher when model parameters from reconstructed trajectories are applied. These results are mainly due to lane changing, and are also the sought indirect validation of the proposed data reconstruction methodology.     

计算机辅助验证正线应答器报文的系统设计

CTCS-2级应答器报文数据的验证一般采用手工绘图、标注核对的方式。计算机系统通过ADO.NET数据接口导入相关数据,实现自动绘图功能,并使用多缓存的双缓存技术解决拖动时的缓冲和闪烁。采用线性查找和比对技术,实现自动验证部分应答器正线报文数据的功能,为报文分析人员提供有效的辅助手段。     

Farm tractor models for research and development purposes

The modelling problems related to the simulation of the dynamics of farm tractors are dealt with. The aim is to develop reliable mathematical models to speed-up the research and development activities in which farm tractors and their sub-systems (driveline, steering and suspension system, etc.) are to be conceived and designed. Two models of farm tractors have been developed. The first model is based on a proprietary software, able to quickly simulate the motion of a vehicle on smooth or rough soil. The second model has been developed by the commercial software ADAMS/Car^®, which allows to model complicated transmission and suspension systems. In both of the two models, the tyres, the transmission system, the suspension system, the steering system, the engine and the body inertia are carefully described mathematically. Both of the two models are defined in a parametric way. Particular attention has been devoted to the measurements of the tyre characteristic and of the inertia parameters of the farm tractor body. For the measurement of tyre characteristics, a new instrumented wheel hub has been used. The accurate measurement of both the tyre characteristic and body inertia tensor has allowed a good agreement between measured and computed time histories referring to a number of validation manoeuvres performed either on-road or off-road. The derived farm tractor models could simulate the working conditions of a generic farm tractor while hauling a plough or while running at a relatively high speed on a rough soil or while steering on a sloped, soft surface.     

Ship resistance when operating in floating ice floes: Derivation,validation, and application of an empirical equation

With the effects of global warming, the Arctic is presenting a new environment where numerous ice floes are floating on the open sea surface. Whilst this has improved Arctic shipping navigability in an unprecedented way, the interaction of such floes with ships is yet to be understood to aid the designing of ships and route planning for this region. To further explore this topic, the present work develops a procedure to derive an empirical equation that can predict the effects of such floes on ship resistance. Based on a validated computational approach, extensive data are extracted from simulations of three different ships with varying operational and environmental conditions. The ice-floe resistance is shown to strongly correlate with ship beam, ship buttock angle, ship waterline angle, ship speed, ice concentration, ice thickness and floe diameter, and the regression powers of each of the parameters on resistance are ascertained. This leads to a generic empirical equation that can swiftly predict ice-floe resistance for a given ship in a given condition. Subsequently, demonstrations are given on the incorporation of the derived equation into a set of real-time Arctic ship performance model and voyage planning tool, which can predict a ship's fuel consumption in ice-infested seas and dynamically suggest a route with the least safety concern and fuel consumption. Moreover, the equation is validated by providing ice resistance prediction for experimental and full-scale conditions from multiple sources, showing high accuracy. In conclusion, the empirical equation is shown to give valid and rapid estimates for ice-floe resistance, providing valuable insights into ship designs for the region, as well as facilitating practical applications for polar navigation.