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51.
With the rapid growth of traffic in urban areas, concerns about congestion and traffic safety have been heightened. This study leveraged both Automatic Vehicle Identification (AVI) system and Microwave Vehicle Detection System (MVDS) installed on an expressway in Central Florida to explore how congestion impacts the crash occurrence in urban areas. Multiple congestion measures from the two systems were developed. To ensure more precise estimates of the congestion's effects, the traffic data were aggregated into peak and non-peak hours. Multicollinearity among traffic parameters was examined. The results showed the presence of multicollinearity especially during peak hours. As a response, ridge regression was introduced to cope with this issue. Poisson models with uncorrelated random effects, correlated random effects, and both correlated random effects and random parameters were constructed within the Bayesian framework. It was proven that correlated random effects could significantly enhance model performance. The random parameters model has similar goodness-of-fit compared with the model with only correlated random effects. However, by accounting for the unobserved heterogeneity, more variables were found to be significantly related to crash frequency. The models indicated that congestion increased crash frequency during peak hours while during non-peak hours it was not a major crash contributing factor. Using the random parameter model, the three congestion measures were compared. It was found that all congestion indicators had similar effects while Congestion Index (CI) derived from MVDS data was a better congestion indicator for safety analysis. Also, analyses showed that the segments with higher congestion intensity could not only increase property damage only (PDO) crashes, but also more severe crashes. In addition, the issues regarding the necessity to incorporate specific congestion indicator for congestion's effects on safety and to take care of the multicollinearity between explanatory variables were also discussed. By including a specific congestion indicator, the model performance significantly improved. When comparing models with and without ridge regression, the magnitude of the coefficients was altered in the existence of multicollinearity. These conclusions suggest that the use of appropriate congestion measure and consideration of multicolilnearity among the variables would improve the models and our understanding about the effects of congestion on traffic safety. 相似文献
52.
Modeling road safety development can provide important insight into policies for the reduction of traffic fatalities. In order to achieve this goal, both the quantifiable impact of specific parameters, as well as the underlying trends that cannot always be measured or observed, need to be considered. One of the key relationships in road safety links fatalities with risk and exposure, where exposure reflects the amount of travel, which in turn translates to how much travelers are exposed to risk. In general two economic variables: GDP and unemployment rate are selected to analyse the statistical relationships with some indicators of road accident fatality risk.The objective of this research is to provide an overview of relevant literature on the topic and outline some recent developments in macro-panel data analysis that have resulted in ongoing research that has the potential to improve our ability to forecast traffic fatality trends, especially under turbulent financial situations. For this analysis, time series of the number of fatalities and GDP in 30 European countries for a period of 38 years (1975–2012) are used. This process relies on estimating long-term models (as captured by long term time-series models, which model each country separately). Based on these developments, utilizing state-of-the-art modelling and analysis techniques such as the Common Correlated Effects Mean Group estimator (Pesaran), the long-term elasticity mean value equals 0.63, and is significantly different from zero for 10 countries only. When we take away the countries, where the number of fatalities is stationary, the average elasticity takes a higher value of nearly 1. This shows the strong sensitivity of the estimate of the average elasticity over a panel of European countries and underlines the necessity to be aware of the underlying nature of the time series, to get a suitable regression model. 相似文献
53.
《Computer Integrated Manufacturing Systems》1990,3(4):216-222
In recent years, the major emphasis of CIM research and development activity has been in the area of automated manufacturing, where technical and economic feasibility is critical for a viable CIM environment. However, to achieve a truly integrated manufacturing environment, it is necessary to integrate design activities into the structure. Although computers have been used for many years in the design process the present situation is not satisfactory, particularly for small and medium-sized industries. In most cases, computer-aided drafting tools are provided, but they are seldom integrated into the design process and the dependent analysis tools are still only available via separate and frequently unrelated analysis codes. Possible ways of improving the situation are discussed: these include improving the robustness of analysis codes by error estimation, adaptive meshing and postprocessing features, and providing an effective integrated environment, with drafting and design tools. 相似文献
54.
Electromagnetic actuators show considerable promise in replacing camshafts in automotive combustion engines. Most research published to date focuses on reducing valve seating velocity. This is usually achieved using a current feed-forward controller during most of the valve travel and a trajectory controller with a fixed trajectory close to the end of travel. Such systems face considerable challenges in the presence of varying combustion forces, since the feed-forward strategy cannot ensure constant starting conditions for the tracking controller. The work shown here replaces the feed-forward controller with an energy based feedback controller. For the tracking controller with feedback linearization at the end of the valve travel, real-time trajectories that adapt to different starting conditions are derived. The algorithms can adapt to large changes in combustion pressure without relying on a priori combustion information. The algorithms are validated using simulations and on an experimental test bed. 相似文献
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56.
Networks and Spatial Economics - This study aimed to investigate how land-use pattern affects crash frequency at traffic analysis zone (TAZ) level. Traffic, road network, land use, population and... 相似文献