Systemwide implications of the repeal of the national maximum speed limit

The adoption of higher rural interstate speed limits may shift behaviors in ways that broadly affect motor vehicle safety. In particular, these laws may attract drivers from less safe rural noninterstate roadways, implying that any negative implications of higher speed limits for rural interstate fatalities may be attenuated by fewer rural noninterstate fatalities. We test for the reallocation of vehicle miles traveled and fatalities using 1982-2002 U.S. data spanning the relaxation and repeal of the national maximum speed limit (NMSL) across all drivers and specifically those younger and older drivers associated with higher fatality risks. Overall, we find that the repeal of the NMSL resulted in a 36-37% increase in fatalities on rural interstate highways. However, we found very little support for any decrease in rural noninterstate driving or fatalities following the adoption of higher speed limits on rural interstates.     

Safety effects of reducing the speed limit from 90 km/h to 70 km/h

Speed is one of the main risk factors in traffic safety, as it increases both the chances and the severity of a crash. In order to achieve improved traffic safety by influencing the speed of travel, road authorities may decide to lower the legally imposed speed limits. In 2001 the Flemish government decided to lower speed limits from 90 km/h to 70 km/h on a considerable number of highways. The present study examines the effectiveness of this measure using a comparison group before- and after study to account for general trend effects in road safety. Sixty-one road sections with a total length of 116 km were included. The speed limits for those locations were restricted in 2001 and 2002. The comparison group consisted of 19 road sections with a total length of 53 km and an unchanged speed limit of 90 km/h throughout the research period. Taking trend into account, the analyses showed a 5% decrease [0.88; 1.03] in the crash rates after the speed limit restriction. A greater effect was identified in the case of crashes involving serious injuries and fatalities, which showed a decrease of 33% [0.57; 0.79]. Separate analyses between crashes at intersections and at road sections showed a higher effectiveness at road sections. It can be concluded from this study that speed limit restrictions do have a favorable effect on traffic safety, especially on severe crashes. Future research should examine the cause for the difference in the effect between road sections and intersections that was identified, taking vehicle speeds into account.     

The impacts of speed cameras on road accidents: An application of propensity score matching methods

This paper aims to evaluate the impacts of speed limit enforcement cameras on reducing road accidents in the UK by accounting for both confounding factors and the selection of proper reference groups. The propensity score matching (PSM) method is employed to do this. A naïve before and after approach and the empirical Bayes (EB) method are compared with the PSM method. A total of 771 sites and 4787 sites for the treatment and the potential reference groups respectively are observed for a period of 9 years in England. Both the PSM and the EB methods show similar results that there are significant reductions in the number of accidents of all severities at speed camera sites. It is suggested that the propensity score can be used as the criteria for selecting the reference group in before-after control studies. Speed cameras were found to be most effective in reducing accidents up to 200 meters from camera sites and no evidence of accident migration was found.     

Effects of average speed enforcement on speed compliance and crashes: A review of the literature

Average speed enforcement is a relatively new approach gaining popularity throughout Europe and Australia. This paper reviews the evidence regarding the impact of this approach on vehicle speeds, crash rates and a number of additional road safety and public health outcomes. The economic and practical viability of the approach as a road safety countermeasure is also explored. A literature review, with an international scope, of both published and grey literature was conducted. There is a growing body of evidence to suggest a number of road safety benefits associated with average speed enforcement, including high rates of compliance with speed limits, reductions in average and 85th percentile speeds and reduced speed variability between vehicles. Moreover, the approach has been demonstrated to be particularly effective in reducing excessive speeding behaviour. Reductions in crash rates have also been reported in association with average speed enforcement, particularly in relation to fatal and serious injury crashes. In addition, the approach has been shown to improve traffic flow, reduce vehicle emissions and has also been associated with high levels of public acceptance. Average speed enforcement offers a greater network-wide approach to managing speeds that reduces the impact of time and distance halo effects associated with other automated speed enforcement approaches. Although comparatively expensive it represents a highly reliable approach to speed enforcement that produces considerable returns on investment through reduced social and economic costs associated with crashes.     

The paradox of driving speed: two adverse effects on highway accident rate

Whereas speeding is known to be a substantial risk factor in driving, there is no unequivocal evidence that accident rate on limited-access motor highways is considerably affected by average speed or by speed limits meant to regulate it. It is suggested here that the seeming puzzle actually may have a straightforward explanation: accident-prone interactions (APIs) between cars occur when they pass each other--mostly moving in the same directions or in opposite ones. Such interactions are shown here to happen more frequently, the lower average speed is. To the extent that high speed limits contribute to increase in average speed, they serve to reduce the number of such interactions, thereby to moderate at least part of the negative effect of speed on the driver's ability to avoid an impending accident.     

Development of a variable speed limit strategy to reduce secondary collision risks during inclement weathers

Inclement weather reduces traveler's sight distance and increases vehicle's stopping distance. Once a collision occurred during inclement weather and resulted in a slow traffic, approaching vehicles may not have adequate time to make emergency responses to the hazardous traffic, resulting in increased potentials of secondary collisions. The primary objective of this study is to develop a control strategy of variable speed limits (VSL) to reduce the risks of secondary collisions during inclement weathers. By analyzing the occurrence condition of secondary collision, the VSL strategy is proposed to dynamically adjust the speed limits according to the current traffic and weather conditions. A car-following model is modified to simulate the vehicle maneuvers with the VSL control. Two surrogate safety measures, based on the time-to-collision notion, are used to evaluate the control effects of VSL. Five weather scenarios are evaluated in simulation. The results show that the VSL strategy effectively reduces the risks of secondary collisions in various weather types. The time exposed time-to-collision (TET) is reduced by 41.45%–50.74%, and the time integrated time-to-collision (TIT) is reduced by 38.19%–41.19%. The safety effects are compared to those with a previous VSL strategy. The results show that in most cases our strategy outperforms the previous one. We also evaluate how driver's compliance to speed limit affects the effectiveness of VSL control.     

The effects of an edgeline on speed and lateral position: a meta-analysis

This paper presents a meta-analysis of studies that have evaluated the effects of an edgeline on speed and lateral position of motorised road users. Together with many other study characteristics, 41 estimates of the effects of an edgeline on speed and 65 on lateral position were extracted from the studies. The results of the evaluation studies show a great variety in effects. Both negative and positive effects on speed and lateral position were found; amongst others, increases in speed up to 10.6 km/h, as well as decreases in speed up to 5.0 km/h, and shifts of the lateral position towards the centre of the road up to 30 cm, as well as shifts towards the edge of the road up to 35 cm. Further analyses resulted in the determination of study characteristics that influence the effects of an edgeline on speed and lateral position. It is concluded that the effects of an edgeline on speed are related to the presence of a centreline. Applying an edgeline to a road without a centreline increases the speed of road users, and replacing a centreline by an edgeline decreases the speed. Results with respect to adding an edgeline to a road with a centreline were unclear. Another conclusion is that shoulder width and road environment contribute to the effects of an edgeline on lateral position. In combination with wide shoulders or buildings and/or trees next to the road, edgelines lead to shifts of the lateral position towards the edge of the road, and in combination with narrow shoulders or open fields, edgelines lead to shifts towards the centre of the road.     

Effect of repeal of the national maximum speed limit law on occurrence of crashes, injury crashes, and fatal crashes on Utah highways

Speed limits were increased in Utah and other States after repeal of the national maximum speed limit law (NMSL) in 1995. This study analyzed effects of the increased speed limit on Utah highways on crash rates, fatality crash rates, and injury crash rates. Annual (1992-1999) rates of crashes, fatality crashes, and injury crashes for the following highway categories were calculated: urban Interstate segments (current speed limit 60-65 miles per hour (mph)); rural Interstate segments (current speed limit 70-75 mph); 55 mph rural non-Interstate highway segments; and high-speed non-Interstate highways (current speed limit 60-65 mph). Data were analyzed using autoregressive integrative moving average intervention time series analysis techniques. There were significant increases in total crash rates on urban (60-65 mph) Interstate segments (confounded by extensive ongoing highway construction on these highways), and in fatal crash rates on high-speed (60-65 mph) rural non-Interstate segments. The following variables were unaffected: total, fatality, and injury crash rates on rural Interstate segments; fatality and injury crash rates on urban Interstate segments; total and injury crash rates on high-speed non-Interstate segments. These results show an adverse effect on crash occurrence for subsets of crash types and highways, but do not show a major overall effect of NMSL repeal and increased speed limit on crash occurrence on Utah highways.     

Effects of local wall thinning on plastic limit loads of elbows using geometrically linear FE limit analyses

This paper provides closed-form plastic limit load solutions for elbows under in-plane bending and internal pressure, via three-dimensional (3D), geometrically linear FE limit analyses using elastic-perfectly plastic materials. Wide ranges of elbow and thinning geometries are considered. To investigate the effect of the axial thinning length on limit loads systematically, two limiting cases are considered; a sufficiently long thinning, and the circumferential part-through surface crack. Closed-form plastic limit load solutions for wall thinning with intermediate longitudinal extents are then obtained from these two limiting cases. The effect of the axial extent of wall thinning on plastic limit loads for elbows is highlighted by comparing that for straight pipes. Although the proposed solutions are developed for the case when wall thinning exists in the center of elbows, it is also shown that they can be applied to the case when thinning exists anywhere within the elbow.     

The effect of material hardness and mean stress on the fatigue limit of steels containing small defects

Fatigue tests on material containing small defects were performed under a wide range of mean stress for three grades of steels with different hardness. The ΔK_th of small defects had a peculiar dependency on material hardness and mean stress, which was quite different from those of long cracks or plain specimens. The crack closure of short cracks was measured. It was shown that the formation of the crack closure was affected by the material hardness and mean stress. This behaviour of crack closure resulted in characteristic fatigue limit properties of materials containing small defects.     

A note on the limit load of welded joints of a rectangular cross-section

A flat layer of a rigid perfectly plastic material subjected to tension between two rigid blocks is considered. The layer is assumed to have a rectangular cross-section. The influence of the ratio of the in-plane layer dimensions on the limit load and the maximum tensile stress is studied. Comparison with numerical calculations of the limit load based on the assumption of the plane strain conditions is made.     

Method of determining the systematic variation of the frequency of a driving oscillator situated on a moving object

A new approach to the determination of the systematic variation in the frequency of onboard time and frequency standards located on intermediate-altitude space vehicles is considered.Translated from Izmeritelnaya Tekhnika, No. 10, pp. 27–30, October, 2004.     

Influence of anisotropy on a limit load of weld strength overmatched middle cracked tension specimens

ABSTRACT A plane‐strain upper bound limit load solution for weld strength overmatched middle cracked tension specimens (M(T) specimens), is found. It is assumed that the weld material is isotropic, but the base material is orthotropic and its axes of orthotropy are straight and parallel to the axes of symmetry of the specimen. A quadratic orthotropic yield criterion is adopted. The solution is based on a simple discontinuous kinematically admissible velocity field and is an extension of the corresponding solution for the specimen made of isotropic materials. These two solutions are compared to demonstrate the influence of anisotropy on the magnitude of the limit load.     

Impact of BAC limit reduction on different population segments: a Poisson fixed effect analysis

Over the past few decades, several countries enacted the reduction of the legal blood alcohol concentration (BAC) limit, often alongside the administrative license revocation or suspension, to battle drinking-and-driving behavior. Several researchers investigated the effectiveness of these policies by applying different analysis procedures, while assuming population homogeneity in responding to these laws.

The present analysis focuses on the evaluation of the impact of BAC limit reduction on different population segments. Poisson regression models, adapted to account for possible observation dependence over time and state specific effects, are estimated to measure the reduction of the number of alcohol-related accidents and fatalities for single-vehicle accidents in 22 U.S. jurisdictions over a period of 15 years starting in 1990.

Model estimates demonstrate that, for alcohol-related single-vehicle crashes, (i) BAC laws are more effective in terms of reduction of number of casualties rather than number of accidents, (ii) women and elderly population exhibit higher law compliance with respect to men and to young adult and adult population, respectively, and (iii) the presence of passengers in the vehicle enhances the sense of responsibility of the driver.     

Effect of circular holes on the ratchet limit and crack tip plastic strain range in a centre cracked plate

In this paper a centre cracked plate subjected to cyclic tensile loading and cyclic bending moment is considered. The effect of circular holes drilled in the region of the crack tip on the ratchet limit and crack tip plastic strain range is studied. Direct evaluation of the ratchet limit and crack tip plastic strain range is solved by employing the new Linear Matching Method (LMM). Parametric studies involving hole diameter and location are investigated. The optimum hole location for reducing the crack tip plastic strain range with the least reduction in ratchet limit is identified, and located at a distance 10% of the semi-crack length from the crack tip on the side opposite the ligament for both cyclic tensile loading and cyclic bending moment cases. It is also observed that the optimum location is independent of the hole size for both cyclic loading cases.     

Effects of crystallinity and chemical variation on apparent band-gap shift in polycrystalline indium nitride

The nature of the apparent band-gap shift in polycrystalline indium nitride thin-films, grown by remote-plasma-enhanced chemical vapour deposition at 535 ± 10 °C, has been investigated separately in relation to growth temperature dependent crystallinity and chemical variation. Substrates of sapphire and gallium nitride on sapphire were used to study the effect of a stress-reduced template on indium nitride crystallite quality and apparent band-gap. To mimic surface growth temperature variations two glass substrates of differing thickness and thermal conductivity were intentionally used for the same growth conditions. The samples were characterised using optical transmission, scanning electron microscope, X-ray diffraction, and high-resolution X-ray photoelectron spectroscopy. The results indicate that the apparent band-gap shift in polycrystalline narrow band-gap indium nitride thin-films is not primarily determined by the quality of indium nitride crystallites but rather it is associated with growth temperature dependent chemical variations in the films.     

消能伸臂体系减震性能的参数变异性影响分析

为研究结构参数变异性对消能伸臂体系减震性能的影响,推导了该体系的有限元振动方程,同时提出地震响应简化分析的"Maxwell型阻尼器计算法",并结合Gauss-Hermite降维算法分析了确定性激励、随机地震激励作用的参数变异影响情况.结果表明:Gauss-Hermite降维算法既能保证精度又能提高计算效率;确定性激励时...     

微光环境下显示器（CRT）颜色视标呈现时间对颜色视标辨别的影响

该研究在控制颜色视标呈现距离、颜色视标亮度的条件下,以正确率为指标,探讨了在微光环境下,颜色视标呈现时间对CRT显示器颜色视标辨别的影响作用。实验中,颜色视标的呈现时间有0．5s、1s、1．5s、3个水平。实验结果表明：在环境亮度为0．5cd/m^3的微光环境下,8种颜色视标的呈现时间对被试正确辨别颜色的绩效有明显的影响,而且呈现时间越短,被试辨别颜色绩效越差。当视标呈现时间为1．5s时,被试对8种视标的平均辨别颜色正确率达到90％以上。     

Effects of Pay-As-You-Drive vehicle insurance on young drivers' speed choice: results of a Dutch field experiment

Speeding is an important cause for young drivers’ involvement in traffic accidents. A reduction in driving speeds of this group could result in fewer accidents. One way of reducing driving speed is offering explicit financial incentives. In collaboration with five Dutch car insurance companies, we tested the effects of a Pay-As-You-Drive insurance fee on driving speed. A group of young drivers could save money on their monthly insurance fee by keeping the speed limit. Driving speed was monitored through GPS technology during one year. Analyses showed that, relative to pre- and post-measurement, as well as a control group, the introduction of a Pay-As-You-Drive insurance fee significantly reduced speed violations of young drivers.     

Effects of the relative speed of a magnet moving to and from a single-domain YBCO bulks on their interaction force

Two single-domain YBCO bulks with different grain orientations were used to investigate the effect of relative moving speed between the magnet and YBCO bulk, on their interaction force at LN₂ temperature under zero field cooling (ZFC) state. It is found that the levitation force of the sample S1 with c-axis perpendicular to the top surface is higher than that of the sample S2 with c-axis parallel to the top surface; the maximum levitation force (F_ML) is increasing with the increase of relative moving speed (V_RMS) between the magnet and the samples at first and reaches a peak value for sample S1 and a peak zone values for sample S2, then the F_ML decreases with the increase of V_RMS; the stiffness between the samples and the magnet is decreasing with the increase of the V_RMS. This result is useful for the application of superconducting levitation.