identify relevant studies by a systematic search and then use effect size standardizing on each study result. In addition, this approach corrects sampling error and other artifacts, and it can present an estimate of the total effect with minimized subjectivity (5). Further, since different studies might be influenced by methodologies, time span, and regions, hierarchy meta-analysis has been applied using these factors as grouping variables. Separate analyses are conducted for each group.The process used in the meta-analysis is outlined in Figure 1. After careful review of the included articles, two separate meta-analyses were conducted separately for comparison studies and regression studies.For regression studies, measures of weather conditions were taken as the continuous variable. Effect size and percent change in crash rate were both applied to standardize the research results. However, due to space limitations of this paper, those results are not presented; they may be found in Qiu (6).For the comparison studies, measures of weather conditions were considered as a binary variable (such as snow versus nonsnow). In addition to the overall meta-analysis carried out for each weather category (snow, rain, etc.), hierarchy meta-analyses were conducted separately for the comparison studies stratified by decades (time span) and by countries. METHOD Literature SearchA literature search for relevant studies published from 1970 to 2005 was conducted for both peer-reviewed literature and unpublished technical reports and theses. Search strategies used ensured this study contained enough primary studies for meta-analysis, because meta-analysis based on a large number of studies with a small sample size has been shown to be more accurate than that based on a small number of studies with large sample sizes (5).Following the search, 376 papers and reports were selected for further examination, of which 108 were determined to be pertinent. From those reports, 34 that provided 78 result records were selected for meta-analysis. Study Inclusion Criteria and CodingPrevious studies that explored the association between weather conditions and traffic safety have investigated diverse variables. These studies have also applied a variety of methods and were based on Adverse weather obviously has an impact on vehicle crash rates on roads and highways. However, it would be valuable to quantify the extent to which weather conditions affect the crash rate. To do that, a meta-analysis has been conducted to generalize research findings on this subject and attempt to quantify the impact of weather on traffic crashes. Studies between 1967 and 2005 that examined the interaction of weather and traffic safety were reviewed. Thirty-four papers and 78 records that meet the predetermined criteria were included in the analysis. Crash rates from each study were normalized with respect to effect size for meta-analysis generalization. Results indicate that the crash rate usually increases during precipitation. Snow has a greater effect than rain does ...

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Tensile tests have been performed on first-year sea ice and on laboratory-grown saline ice at −10° C and at two strain rates, 10−3 s−1 and 10−7 s−1. The first-year sea ice was collected from the Beaufort Sea in April of 1983 and November of 1984. The laboratory-grown saline ice was grown unidirectionally downward by means of a cooling plate on an insulated tank. The ice was loaded both parallel (vertical orientation) and perpendicular (horizontal orientation) to its growth direction. The results showed brittle behavior at the higher rate for both orientations, but ductile behavior at the lower rate for the horizontally loaded ice. At both strain rates, both the tangent modulus and the tensile strength are significantly higher along the vertical direction. The structure and mechanical properties of the laboratory-grown ice were similar to those of the first-year sea ice, indicating that the laboratory ice is a covenient and economical material for studying the mechanical properties of columnar saline ice.

Tests have been performed at −10°C on circumferentially notched right circular cylinders of randomly oriented granular polycrystalline freshwater ice, to determine whether grain size affects fracture toughness (KIc). Grain sizes, as measured by the linear intercept method, varied from 1.6 mm to 9.3 mm in diameter. The circumferentially notched specimen was used because of the ease with which it can be manufactured from right circular cylinders, made regularly and with considerable accuracy of alignment for some years now by workers of the Thayer School Ice Research Laboratory. A slight (25 percent) decrease in values of KIc is observed as grain size increases over the range investigated. Consideration is given to the cause of this effect and to its possible contribution to the scatter in KIc values observed by earlier workers. Other possible causes of this scatter are indicated.

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Experiments have been performed to determine the effect of loading rate and temperature on the fracture toughness of both granular and S2 columnar freshwater ice. Loading rate was varied from 0.04 to 40.0 kPam s-1, and over this range the fracture toughness was observed to decrease from 201 to 109 kPam. Examination of load—CMOD curves indicate that at a loading rate of 40 kPam s-1, the crack tip plasticity was sufficiently limited that the specimen behavior can be considered linear elastic, thus providing a valid Kq measurement. When test temperature was varied from −5 to −45°C for the S2 columnar ice, no significant variation in toughness was observed. In contrast, for granular ice, a higher toughness (144 kPam) was observed in the −5 to −20°C range than for the S2 columnar ice. However, the toughness of the granular ice at−45°C is not significantly different from that of the S2 columnar ice. A companion paper (Weber and Nixon, 1996) analyzes the results in greater detail comparing them with previous work, and presents a detailed fractographic analysis of the failure surfaces.

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