Congestion and Safety: A Spatial Analysis of London

Spatially disaggregate Enumeration District (ED) level data for London is used in an analysis of various area-wide factors on road casualties. Data on 15335 EDs was input into a geographic information system (GIS) that contained data on road characteristics, public transport accessibility, information of nearest hospital location, car ownership and road casualties. Demographic data for each ED was also included. Various count data models e.g., negative binomial or zero-inflated Poisson and negative binomial models were used to analyze the associations between these factors with traffic fatalities, serious injuries and slight injuries. Different levels of spatial aggregation were also examined to determine if this affected interpretation of the results. Different pedestrian casualties were also examined. Results suggest that dissimilar count models may have to be adopted for modeling different types of accidents based on the dependent variable. Results also suggest that EDs with more roundabouts are safer than EDs with more junctions. More motorways are found to be related to fewer pedestrian casualties but higher traffic casualties. Number of households with no car seems to have more traffic casualties. Distance of the nearest hospital from EDs tends to have no significant effect on casualties. In all cases, it is found that EDs with more employees are associated with fewer casualties.

Lip rounding in Amoy and Mandarin high vowels: maximum dispersion, or adequate separation

There are two hypotheses about the relationship between phonological contrasts and phonetic feature scales. Some phoneticians propose that values are chosen so that contrasting phonemes are maximally separated, e.g., Lilijencrants and Lindblom, 1972, while others claim that they need only to be adequately separated, e.g., Maddieson, 1977. This paper tests the competing hypotheses by comparing lip position in Mandarin [i], [y], [u] with that of Amoy [i] and [u]. According to adequate separation, the lip spreadness/roundness of Mandarin will be more extreme than that of Amoy, since there are three high vowels in Mandarin but only two in Amoy. According to the maximum dispersion hypothesis, the degree of roundness should be the same in both languages. Amoy and Mandarin data were collected from three bilingual speakers. The results support the Adequate Separation Theory. This paper also tests Wood's (1986) claim that in a language with two high rounded vowels, /u/ and /y/, /u/ is more rounded than /y/. The result shows that this claim is not necessarily true

Map-matching in complex urban road networks

Global Navigation Satellite Systems (GNSS) such as GPS and digital road maps can be used for land vehicle navigation systems. However, GPS requires a level of augmentation with other navigation sensors and systems such as Dead Reckoning (DR) devices, in order to achieve the required navigation performance (RNP) in some areas such as urban canyons, streets with dense tree cover, and tunnels. One of the common solutions is to integrate GPS with DR by employing a Kalman Filter (Zhao et al., 2003). The integrated navigation systems usually rely on various types of sensors. Even with very good sensor calibration and sensor fusion technologies, inaccuracies in the positioning sensors are often inevitable. There are also errors associated with spatial road network data. This paper develops an improved probabilistic Map Matching (MM) algorithm to reconcile inaccurate locational data with inaccurate digital road network data. The basic characteristics of the algorithm take into account the error sources associated with the positioning sensors, the historical trajectory of the vehicle, topological information on the road network (e.g., connectivity and orientation of links), and the heading and speed information of the vehicle. This then enables a precise identification of the correct link on which the vehicle is travelling. An optimal estimation technique to determine the vehicle position on the link has also been developed and is described. Positioning data was obtained from a comprehensive field test carried out in Central London. The algorithm was tested on a complex urban road network with a high resolution digital road map. The performance of the algorithm was found to be very good for different traffic maneuvers and a significant improvement over using just an integrated GPS/DR solution