Ag Wood

Methodology for fitting and updating predictive accident models with trend

Reliable predictive accident models (PAMs) (also referred to as Safety Performance Functions (SPFs)) have a variety of important uses in traffic safety research and practice. They are used to help identify sites in need of remedial treatment, in the design of transport schemes to assess safety implications, and to estimate the effectiveness of remedial treatments. The PAMs currently in use in the UK are now quite old; the data used in their development was gathered up to 30 years ago. Many changes have occurred over that period in road and vehicle design, in road safety campaigns and legislation, and the national accident rate has fallen substantially. It seems unlikely that these ageing models can be relied upon to provide accurate and reliable predictions of accident frequencies on the roads today. This paper addresses a number of methodological issues that arise in seeking practical and efficient ways to update PAMs, whether by re-calibration or by re-fitting. Models for accidents on rural single carriageway roads have been chosen to illustrate these issues, including the choice of distributional assumption for overdispersion, the choice of goodness of fit measures, questions of independence between observations in different years, and between links on the same scheme, the estimation of trends in the models, the uncertainty of predictions, as well as considerations about the most efficient and convenient ways to fit the required models.

Successive regressions and transgressions in the Neogene

Abstract Sparker traverses off the coasts of Wales, southern Ireland, Devon and Cornwall reveal an extensive platform with a slope of less than 1 in 1000 cut into Palaeozoic rocks. It is shown that the platform extends without change of slope from Palaeozoic rocks onto Cretaceous, Oligocene and (?)Miocene beds. Five regressions and transgressions can be traced, and a tentative explanation is advanced for the slow transgression phases.

Updating outdated predictive accident models

Reliable predictive accident models (PAMs) (also referred to as safety performance functions (SPFs)) are essential to design and maintain safe road networks however, ongoing changes in road and vehicle design coupled with road safety initiatives, mean that these models can quickly become dated. Unfortunately, because the fitting of sophisticated PAMs including a wide range of explanatory variables is not a trivial task, available models tend to be based on data collected many years ago and seem unlikely to give reliable estimates of current accidents. Large, expensive studies to produce new models are likely to be, at best, only a temporary solution. This paper thus seeks to develop a practical and efficient methodology to allow currently available PAMs to be updated to give unbiased estimates of accident frequencies at any point in time. Two principal issues are examined: the extent to which the temporal transferability of predictive accident models varies with model complexity; and the practicality and efficiency of two alternative updating strategies. The models used to illustrate these issues are the suites of models developed for rural dual and single carriageway roads in the UK. These are widely used in several software packages in spite of being based on data collected during the 1980s and early 1990s. It was found that increased model complexity by no means ensures better temporal transferability and that calibration of the models using a scale factor can be a practical alternative to fitting new models.

The Origin of the Structure known as Guilielmites

During the course of palaeontological work in the North Wales coalfield, shining discoidal bodies were noticed on the bedding planes of various shales. They were found to be identical with objects described as Guilielmites by Geinitz (4) in 1858. The literature concerning them is reviewed below, and a new theory of their origin is advanced.

An Excavation revealing the junction between Ingletonian and Coniston Limestone at Ingleton

A section along the contact between the Silurian Ingleton and Coniston limestone beds was excavated at Ingleton, England, as a demonstration for students.

Fish Remains from the North Wales Coalfield

AT certain levels in the Coal Measures of North Wales a flood of fish scales and bones occurs, to the exclusion of almost every other fossil; at others only an isolated scale or tooth is seen. The area appears to be especially rich in fish remains, though possibly this is due to inadequate collecting in other areas. A summary of the succession in the Flintshire and Denbighshire portions of the coalfield is shown in the diagram on p. 483, while the area dealt with is shown on the map (p. 482).

Updating predictive accident models of modern rural single carriageway A-roads

Abstract Reliable predictive accident models (PAMs) are essential to design and maintain safe road networks, and yet the models most commonly used in the UK were derived using data collected 20 to 30 years ago. Given that the national personal injury accident total fell by some 30% in the last 25 years, while road traffic increased by over 60%, significant errors in scheme appraisal and evaluation based on the models currently in use seem inevitable. In this paper, the temporal transferability of PAMs for modern rural single carriageway A-roads is investigated, and their predictive performance is evaluated against a recent data set. Despite the age of these models, the PAMs for predicting the total accidents provide a remarkably good fit to recent data and these are more accurate than models where accidents are disaggregated by type. The performance of the models can be improved by calibrating them against recent data.

Dynamic Planet: Mercury in the Context of Its Environment

Mercury, the Suns nearest neighbor, is tantalizingly close to the Earth yet is one of the least explored objects in our solar system. The planets proximity to the Sun makes Earth-based observations extremely difficult, and the harsh environment presents a significant challenge to spacecraft. Nevertheless, we are currently on the verge of a new era of exploration of this fascinating, mysterious, and largely uncharted world. Much of our knowledge about Mercury has come from just three flybys by NASAs Mariner 10 spacecraft in the mid-1970s. This mission sent back stunning images of about 45% of the planets surface and made the truly puzzling discovery of a magnetic field, the source of which is still unknown. Currently, NASAs Mercury Surface, Space Environment, Geochemistry, and Ranging (MESSENGER) mission is beginning to explore Mercury and aims to answer many unresolved questions about the structure, composition, magnetic field, and history of this incredible world. To date, MESSENGER has conducted two flybys and is expected to go into orbit around Mercury in March 2011. Later, in 2013, the European Space Agencys BepiColombo mission, which uses a twin spacecraft approach, will head for the planet to understand the detail of this dynamic system.

Verticillopora and Phragmoporella , Described as Calcareous Algae, are Crinoid Stems

Study of sections and by serial grinding indicates that fossils described by R. Rezak as new dasycladaceans from Silurian localities of the southwestern United States (Colorado School Mines, Quart. Vol. 54, p. 117-129, 1959) are portions of stems of crinoids resembling European species belonging to the Crotalocrinidae and the Polypeltidae.