Changing speed limit leads to proportional changes in average speeds which may affect the number of traffic accident occurrences. It is however critical and challenging to evaluate the impact of a speed limit alteration on the number and severity of accidents due primarily to the unavailability of adequate data and the inherent limitations of existing approaches. Although speed is regarded as one of the main contributory factors in traffic accident occurrences, research findings are inconsistent. Independent of the robustness of their statistical approaches, accident frequency models typically use accident grouping concepts based on spatial criteria (e.g. accident counts by link termed as a link-based approach). In the link-based approach, the variability of accidents is explained by highly aggregated average measures of explanatory variables that may be inappropriate, especially for time-varying variables such as speed and volume. This thesis re-examines accident-speed relationships by developing a new accident data aggregation method that enables improved representation of the road conditions just before accident occurrences in order to evaluate the impact of a potential speed limit increase on the UK motorways (e.g. from 70 mph to 80 mph). In this work, accidents are aggregated according to the similarity of their pre-accident traffic and geometric conditions, forming an alternative accident count dataset termed as the condition-based approach. Accident-speed relationships are separately developed and compared for both approaches (i.e. link-based and condition-based) by employing the reported annual accidents that occurred on the Strategic Road Network of England in 2012 along with traffic and geometric variables. Accident locations were refined using a fuzzy-logic-based algorithm designed for the study area with 98.9% estimated accuracy. The datasets were modelled by injury severity (i.e. fatal and serious or slight) and by number of vehicles involved (i.e. single-vehicle and multiple-vehicle) using the multivariate Poisson lognormal regression, with spatial effects for the link-based model under a full Bayesian inference method. The results of the condition-based models imply that single-vehicle accidents of all severities and multiple-vehicle accidents with fatal or serious injuries increase at higher speed conditions, particularly when these are combined with lower volumes. Multiple-vehicle slight injury accidents were not found to be related with higher speeds, but instead with congested traffic. The outcomes of the link-based model were almost the opposite; suggesting that the speed-accident relationship is negative. The differences between the results reveal that data aggregation may be crucial, yet so far overlooked in the methodological aspect of accident data analyses. By employing the speed elasticity of motorway accidents that was derived from the calibrated condition-based models it has been found that a 10 mph increase in UK motorway speed limit (i.e. from 70 mph to 80 mph) would result in a 6-12% increase in fatal and serious injury accidents and 1-3% increase in slight injury accidents.

[pt] O transporte rodoviário de produtos perigosos é a principal atividade econômica geradora de acidentes ambientais no Brasil. No modal rodoviário, durante o carregamento, o deslocamento e a descarga há combinações de fatores adversos à operação prescritas em normas que representam riscos de incidentes e acidentes que, a cada ano, aumentam suas estatísticas nas estradas brasileiras. Esta pesquisa identificou pontos de controle aplicados nos locais de partida, onde ocorrem os carregamentos, operados por condutores de veículos que transportam etanol com vistas à prevenção de acidentes durante o transporte da carga. A partir da revisão de leis, decretos e normas, e considerando o percurso entre os estados do Rio de Janeiro e de São Paulo, o transporte rodoviário de produtos perigosos foi estudado sob o ponto de vista da teoria de prevenção de acidentes de Haddon e modelos de acidentes do Abiquim, programa Olho Vivo nas Estradas. Por meio de entrevistas com funcionários de distribuidoras de combustíveis, a pesquisa identificou práticas correntes utilizadas por motoristas de caminhões para a checagem das condições gerais dos veículos nos pontos de partida com vistas ao atendimento de normas, legislações e procedimentos de segurança das empresas. Os motoristas revelaram que os acidentes ocorridos nas estradas ou até mesmo nas áreas urbanas não ocorrem por falhas de inspeção no ponto de partida, mas sim devido a imprudência de outros condutores que não respeitam as leis de trânsito. / [en] Since 2015, resulting from industrial expansion and driven by exports and cargo distribution and storage logistics in Brazil, road transport has grown significantly. Among the products that had increased volumes are chemicals that, by their nature, present risks when handled and transported. This increase in demand for cargo transportation was higher in road transport when compared to other modes of transport, such as waterway and rail. The Fig. 1 presents the configuration of the different modal of dangerous cargo transportation in 2015.