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Alternative intersection layouts may reduce traffic delays and/or improve road safety. Two alternatives are reviewed in this research: 'priority-controlled Seagull intersections' and ‘priority-controlled intersections with a Left Turn Slip Lane’. Seagull intersections are used to reduce traffic delays. Some do experience high crash rates, however. Left Turn Slip Lanes allow turning traffic to move clear of the through traffic before decelerating, thereby reducing the risk of rear-end crashes. Although there is debate about the safety problems that occur at Seagull intersections and Left Turn Slip Lanes there has been very little research to quantify the safety impact of different layouts. In this study, crash prediction models have been developed to quantify the effect of various Seagull intersection and Left Turn Slip Lane designs on the key crash types that occur at priority intersections. The analysis showed that seagulls are not safe on 4-lane roads, that roadway features like kerb-side parking and nearby intersections can increase crash rates and that left turners in LTSLs can restrict visibility and create safety problems.

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Providing rapid and safe traffic in citiesrequires the use of a set of planning and organizational measures.While the implementation of architectural-planning measures requires, except for significant investments, a quite long period, organizational measures can lead, albeit to a temporary but relatively rapid effect. For this purpose, an analysis of traffic flow metricson the approaches to the intersection, traffic light cycle, and the traffic phasing was carried out.Conducted research indicates that left-turn flows cause significant delays andreduce traffic safetyat the intersection.Therefore, increasing the efficiency of the crossroadsneeds redevelopment measuresby restriction of left-turn flowsfrom the main road, change of the traffic flows phasing and optimizing the traffic light cycle. In the presence of adjacent intersections, the scheme of left turn realization is developed. The simulation of intersection functioning in existing conditions and under the change of left-turn flows movement organization was carried out in the PTV Vissim software environment It is established that restriction the left-turn flows atthe controlled intersectionallows optimization the traffic light cycleand equip it so that the average delay for traffic flows will decrease in comparison with the current state
Technical Report
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Accident Prediction Models have been developed for urban and rural intersections and links. This includes models for traffic signals, roundabout, priority and uncontrolled intersections, rural highways, motorways, urban arterials , collector and local streets. Accident (1995 to 1999) and traffic data at over 1000 sites throughout New Zealand were used to develop the models. Test statistics have been prepared showing the goodness-of-fit and confidence intervals of the models. Application of the models in economic appraisal (evaluation) has been discussed along with the changes that would need to be made to the (NZ) Project Evaluation Manual to incorporate the models.
Conference Paper
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This paper reviews model relating accidents to traffic flows, with particular emphasis on the appropriateness of the model form and the statistical technique employed for parameter estimation. The development of generalised linear models for predicting accidents at intersections in New Zealand is then described. It is shown that the new models fit the empirical data better than existing, simpler models. the use of the models for predicting intersection accidents in three networks is described.
The report gives the findings of a study of personal injury accidents at a sample of 84 four-arm roundabouts on main roads in the UK. The study includes small roundabouts and roundabouts of conventional design, in both 30-40 and 50-70 mile/h speed limit zones. Tabulations are given showing accident frequencies, severities, and rates by roundabout type. The accidents are further analyzed by type (entering-circulating, approaching, single-vehicle, etc) and by road-user involvement (cyclist, motorcyclist, pedestrian, etc). The accident frequencies by type are related to traffic flow and roundabout geometry using regression methods. Equations are developed to enable roundabout accidents to be predicted for use in design and appraisal.
The NSW Centre for Road Safety is currently conducting a study to evaluate the safety performances of various unsignalised T-junction configurations on high speed rural roads in NSW. This paper summarises the results of the Stage 1 study involving Seagull T-junctions only. The findings were that two types of crashes, Right Near and Right Through, were predominant among all the crashes, and those that result in casualties. Driver impairment, speeding behaviour and road environment conditions were a factor in a small percentage of these crashes. Of the deemed to be at-fault male drivers, almost two thirds were at and above the age of 67. However, for each of the other age groups below this, there was a higher incidence of female drivers than male drivers involved in Right Near crashes. The former is consistent with other studies on older male drivers. Consistent with the RTA's "safe system approach", key solutions include substantially reduced speeds for through traffic and removal of critical side impact crash types. This may require further investigation prior to implementation.
Testing goodness of fit for a Poisson distribution is routine when the mean is sufficiently large; the scaled deviance G or Pearson's X statistic follow approximate chi-square distributions and perform the task well. When the mean is low, typically less than one, the approximations to chi-square distributions are poor. In this paper we explore the underlying reasons for this behaviour and present a practical resolution of the problem, in both single distribution and regression contexts. An extension to negative binomial models is also given. This research is motivated by a real example drawn from road accident modelling.
Crash Rates at Rural Intersections
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Assessing the safety performance of left-turn facilities at rural T-junctions in New Zealand. University of Auckland Masters Project (788A and 788B)
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