Change In Mean Speed Research Articles

Running Variability in Marathon-Evaluation of the Pacing Variables.

Background and Objectives: Pacing analyses for increasingly popular long-distance running disciplines have been in researchers' spotlight for several years. In particular, assessing pacing variability in long-distance running was hardly achievable since runners must repeat long-running trials for several days. Potential solutions for these problems could be multi-stage long-distance running disciplines. Therefore, this study aimed to assess the long-distance running variability as well as the reliability, validity, and sensitivity of the variables often used for pacing analyses. Materials and Methods: This study collected the split times and finish times for 20 participants (17 men and three women; mean age 55.5 years ± 9.5 years) who completed the multiday marathon running race (five marathons in 5 days), held as part of the Bretzel Ultra Tri in Colmar, France, in 2021. Seven commonly used pacing variables were subsequently calculated: Coefficient of variation (CV), Change in mean speed (CS), Change in first lap speed (CSF), Absolute change in mean speed (ACS), Pace range (PR), Mid-race split (MRS), and First 32 km-10 km split (32-10). Results: Multi-stage marathon running showed low variability between days (Intraclass correlation coefficient (ICC) > 0.920), while only the CV, ACS, and PR variables proved to have moderate to good reliability (0.732 < ICC < 0.785). The same variables were also valid (r > 0.908), and sensitive enough to discern between runners of different performance levels (p < 0.05). Conclusions: Researchers and practitioners who aim to explore pacing in long-distance running should routinely utilize ACS, CV, and PR variables in their analyses. Other examined variables, CS, CSF, MRS, and 32-10, should be used cautiously. Future studies might try to confirm these results using different multi-stage event's data as well as by expanding sensitivity analysis to age and gender differences.

Shared Space and Pedestrian Safety: Empirical Evidence from Pedestrian Priority Street Projects in Seoul, Korea

To provide safe and comfortable walking environments on narrow streets without sidewalks, the Seoul city government has implemented the Pedestrian Priority Street (PPS) projects. Based on Monderman’s “shared space” concept, the PPS involves applying diverse paving design techniques, particularly stamped asphalt pavement of various colors and patterns. This study investigated the effectiveness of the PPS for pedestrian safety. Data sources were (1) video recordings of the nine concurrent PPS in 2014 before and after the projects were completed and (2) a cross-sectional survey at the nine streets. Two groups of multiple regression models analyzed the objective safety, by using the variables, mean vehicle speed and change in mean speed, which were then compared with subjective safety through a questionnaire analysis. The results found that the design strategies reduced the vehicle speed and increased perceptions of pedestrian safety. These suggest that the PPS principles are practical and feasible ways to tackle the safety problems of narrow streets without sidewalks. Further, vehicle speeds increased on streets where the pedestrian zone was clearly distinguishable from the vehicular zone by applying PPS techniques only at the roadside. Thus, clearly separating pedestrians from vehicular zones, which is neither the original principle nor the intent of the PPS, should be avoided.

Effects of higher maximum speed limits to vehicle speeds: A before - after analysis on rural divided highways in Vietnam

This study is to assess the effects of raising speed limits to vehicle operating speeds on rural divided highways in Vietnam. Vehicle speeds were recorded at three different sites of three routes during the daytime and nighttime, both before and after speed limits on these sites increasing from 80 km/h to 90 km/h. The results have shown that the percentage of speeds exceeding speed limits had a wide range from 0% to nearly 30% with regard to different locations, survey time and speed limits. The extent of speeding in some cases was very high even after speed limit increased. It was found that in most cases, the changes in mean speeds after a higher speed limit was applied were statistically significant at the p-value of 0.05, however, the magnitudes of the mean change varied considerably between locations and survey times. Because four out of six cases under the study having mean speeds increased by over 10 km/h after setting up a higher speed limit, this study suggests that further appropriate measures of speed control and speed management should be applied along with increasing speed limit to ensure traffic safety on rural divided highways in Vietnam.&#x0D; Article history: Received 27 March 2018, Revised 18 April 2018, Accepted 27 April 2018

Computational Fluid Dynamics Analysis of a Radial Turbine During Load Step Operation of an Automotive Turbocharger

A method for evaluating the transient performance of a turbocharger (TC) is so-called load step tests. In these tests, the load of the engine is increased at constant engine speed and the time measured from the start to the end of the load step is measured. Usually, these tests can be run relatively late in the development process, since hardware needs to be already available. In order to judge the transient TC performance at an earlier stage, engine process simulations are run using maps of compressor and turbine. For the turbine, these maps usually need to be extrapolated, since only a certain range of each speed line can be measured on a standard gas stand. Furthermore, because of the exhaust gas pulsation of the engine, it is known that the turbine performance differs from the steady-state case which the maps rely on. This has to be respected by additional models. Using computational fluid dynamics (CFD) simulations, the transient performance of the turbine can be analyzed independent from steady-state maps. So far, these investigations have been usually performed with a constant turbine speed. In this paper, a method is presented which includes the speed fluctuations of the TC caused by the exhaust pulsations as well as the change in mean speed during the load step by including compressor and engine in the CFD analysis with User-Fortran models. Results for a load step from 21,000 rpm to 196,400 rpm are discussed.

Impact of vehicle speeds and changes in mean speeds on per vehicle-kilometer traffic accident rates in Japan

Speed and speed variation are widely believed to be key issues in the understanding of traffic accidents. However, there has not been a substantial amount of research that focuses on the interaction between the mean speed and the change in the mean speeds. In this paper we use a five-minute continuous monitoring data of the mean speed on an expressway in Japan. Applying a two dimensional additive Poisson model, we show that not only mean speeds but also changes in mean speeds affect per vehicle-kilometer traffic accident rates. The highest probability of an accident occurs when speed reduces from 110 to 85km/h. Another area of high accident probability occurs when the average speed increases from 65 to 90km/h. In addition, we found that accident rates are higher when there is sunny weather, rather than when it is cloudy.

Evaluation of New Speed Limits in Sweden: A Sample Survey

Objective: The study sought to estimate changes in actual driving speed occurring after new speed limits were introduced in Sweden's rural road network.Method: The effects of speed limit changes were estimated for 7 groups of roads of different types and initial speed limits. To study the effects on the entire road network and not only at specific road sites, a sampling survey was conducted in which speed was measured at randomly selected sites before and after the speed limit changes. Systematic sampling was used to select sites that were widely distributed geographically, though the analysis treats the data as if the sites were selected by simple random sampling. The speed of passing vehicles was generally measured using pneumatic tubes stretched across the road.Results: The survey results indicate that the mean car speed increased by 3.5 km/h when the speed limit increased by 10 km/h on motorways and 2 + 1 roads. Reducing the speed limit by 10 km/h on 2 + 1 roads and rural roads with a speed limit of 110 km/h resulted in a 2 km/h decrease in mean speed. On rural roads where the speed limit was lowered from 90 to 80 km/h, the mean speed decreased by 3.3 km/h. These changes are statistically significant.Conclusions: The present results are in line with previous results indicating an average change in mean speed of approximately 2.5 km/h when the speed limit changes by 10 km/h. The confidence intervals were in most instances fairly small, indicating a sufficiently large number of measurement sites.

Speed and Safety

The speed at which people elect to travel is affected by vehicle and road design; by limits to speed and enforcement of those limits; by traffic control, signs, and markings; and so forth. The speed at which people travel, in turn, affects road safety. In this context two questions arise: ( a) How is the evolution of speed over time and space affected by what drivers do? ( b) How does speed affect safety? This paper reviews what is known, notes the gaps in knowledge, and describes where opinions differ and why. Unfortunately, despite decades of speed measurement and monitoring, the evolution of speed over time is poorly documented, and the understanding of what drives the evolution is largely missing. It is known that speeds evolve over time, but not why; it is known that there is some spillover of the change from one road to another, but its size or extent cannot be predicted. This is a neglected field of inquiry. More is known in answer to Question b. There can be no reasonable doubt that if speed increases while other conditions (vehicles, roads, medical services) remain unchanged, the accidents that occur will tend to be more severe. However, the prevalent and strongly held belief that the greater the speed, the higher is the probability that accidents will occur is, at present, not well supported by research. Even so, given a change in mean speed, one can predict the consequences in injuries and fatalities and this paper discusses how to do so.

Revisiting the Use of Drone Radar to Reduce Speed in Work Zones

Speeding through work zones is a major safety concern in South Carolina. Multiple traffic control devices aimed at reducing speeds in South Carolina work zones were evaluated. The majority of these speed control measures, with the exception of drone radar, were often found not to be practical for widespread, cost-effective implementation. The drone radar device has been tested for more than 20 years, though never before in South Carolina. The focus of this research was to determine the effect of drone radar as a speed reduction measure in work zones on Interstates and secondary highways during day and evening conditions, both for passenger cars and for tractor-trailers. One unique aspect of this study involves the use of a specialized detector to identify vehicles using radar detectors. Most documented research used visual inspection, which is not ideal for this determination, because many vehicles do not have their radar detectors in a visible location. The effectiveness of drone radar was evaluated on the basis of changes in mean speeds, 85th-percentile speeds, and percentage of vehicles exceeding the speed limit. Overall, drone radar caused mean speed reductions of 2 mph for the entire traffic stream. However, individual vehicles equipped with radar detectors reduced speeds ranging from 5 to 8 mph. Drone radar also caused 85th-percentile speeds to decrease between 1 and 5 mph, and a 20% speed reduction was shown in vehicles exceeding the speed limit.

Development and Evaluation of Speed-Activated Sign to Reduce Speeds in Work Zones

Excessive speed is one of the most significant factors contributing to work zone crashes, which, along with work zone fatalities, have increased substantially in the past decade. From the beginning of 2000 to the end of 2003, the number of work zone crashes in South Carolina nearly tripled. In 2005, the South Carolina Department of Transportation initiated a research project to evaluate speed reduction measures in work zones. Through an in-depth literature review of speed control techniques for work zones, it was found that innovative technologies are often too expensive and thus impractical for large-scale implementation. There is a need for less-expensive technologies that are effective in reducing speeds in work zones. Development and evaluation of a speed-activated sign are discussed. Data were collected in work zones on two-lane primary and secondary highways in South Carolina, and the effectiveness of the speed-activated sign was evaluated on the basis of changes in mean speeds, 85th-percentile speeds, and percentages of vehicles exceeding the speed limit. Mean speed reductions ranged from 2 to 6 mph (3.2 to 9.7 km/h) with an average reduction of 3.3 mph (5.3 km/h). This average reduction improved to 4.1 mph (6.6 km/h) at sites where more than 50% of the vehicles were speeding before a sign was introduced. Further research was conducted with two speed-activated signs on a multilane divided highway and an Interstate freeway where similar speed reductions were experienced. From this study, researchers recommend that the speed-activated sign be used in short-term work zones.

The impact of congestion charging on vehicle speed and its implications for assessing vehicle emissions

Previous analysis of London's congestion charging scheme (CCS) has shown that changes in vehicle speed are an important factor in reducing vehicle emissions. Therefore, a detailed investigation of network average vehicle speed in both central and inner London has been undertaken using a combination of the non-parametric Wilcoxon sign ranks test and a method for calculating the cumulative difference between mean speeds pre- and post-CCS, or cumulative sum (CUSUM) analysis. Within the charging zone (CZ), the Wilcoxon test has shown that the difference in speed between pre- and post-CCS periods has increased on average by 2.1 km h −1 and that these changes are significant at the p = 0.05 level. The CUSUM analysis has provided evidence of the timing of this change in mean speed in the CZ and this agrees well with the introduction of the CCS on the 17 February 2003. In combination, these results provide compelling evidence that the introduction of congestion charging has significantly increased vehicle speed in the CZ and by comparison with the results in inner London, that these changes are not part of a wider trend. To examine one impact of this change we used an instantaneous emissions model, the Vehicle Transient Emissions Simulation Software, to undertake a comparison between the change in vehicle emissions associated with changing driving characteristics, between pre- and post-charging periods, and those associated with a change in average speed. The analysis was limited to three vehicle types: a Euro II LGV, a Euro III diesel car and a Euro IV petrol car, but showed that driving characteristics in central London have a relatively small effect on emissions of NO X and CO 2 compared with the average vehicle speed. However, for PM 10 emissions from the Euro II LGV the opposite was found and for this vehicle the driving characteristics were more important than the average speed in estimating exhaust emissions. For this vehicle, emissions increased between pre- and post-CCS periods by 4%. For the Euro IV petrol car NO X emissions also increased by 6% between pre- and post-CCS periods. These findings will help to further understand the extent to which congestion charging reduces vehicle emissions in London.

Are speed enforcement cameras more effective than other speed management measures?: An evaluation of the relationship between speed and accident reductions

In this paper, models are developed which enable a prediction of how the impact of speed management schemes on accidents varies both with speed changes and with site and scheme characteristics. It was found that, the impact of schemes with vertical deflections is independent of the change in mean speed: an accident reduction of 44% is predicted by the model irrespective of the impact on speed. For cameras and other types of engineering schemes, a simple relationship between the change in mean speed and the consequent change in accidents is available. For the range of mean speeds typically found on 30 mph roads, the percentage accident reduction per 1mph speed reduction is around 4% for cameras and 7–8% for schemes with horizontal features. While larger percentage accident reductions are achieved per 1 mph speed reduction on lower speed roads, larger speed reductions and larger overall percentage accident reductions are obtained on roads with higher before mean speeds. It is possible to predict both changes in speeds and accidents before treatment using the models derived from this study and these models confirm that schemes with vertical deflections are most effective in reducing both speeds and accidents.

Measuring the Impacts of Speed Reduction Technologies: Evaluation of Dynamic Advanced Curve Warning System

This paper presents the results of a quantitative and qualitative evaluation of a dynamic curve warning System deployed at one site on Interstate 5 in Oregon. On a dynamic message sign, the System displays messages directed to drivers on the basis of the observed speed of approaching vehicles. For the evaluation, three measures of effectiveness were selected: (a) the change in mean speed for passenger cars and commercial vehicles, (b) the change in the speed distribution for both passenger cars and trucks, and (c) public response to the sign. Speed samples were taken of vehicles with a laser ranging and detection device recording both speed and distance information over 7 days: four in the before period and three in the after period. The quantitative evaluation indicated that the advanced curve warning System was effective in reducing the mean speeds of passenger cars and trucks by approximately 3 mph for the southbound direction and 2 mph for the northbound direction. After the System was installed, the ...

Measuring the Impacts of Speed Reduction Technologies

This paper presents the results of a quantitative and qualitative evaluation of a dynamic curve warning system deployed at one site on Interstate 5 in Oregon. On a dynamic message sign, the system displays messages directed to drivers on the basis of the observed speed of approaching vehicles. For the evaluation, three measures of effectiveness were selected: ( a) the change in mean speed for passenger cars and commercial vehicles, ( b) the change in the speed distribution for both passenger cars and trucks, and ( c) public response to the sign. Speed samples were taken of vehicles with a laser ranging and detection device recording both speed and distance information over 7 days: four in the before period and three in the after period. The quantitative evaluation indicated that the advanced curve warning system was effective in reducing the mean speeds of passenger cars and trucks by approximately 3 mph for the southbound direction and 2 mph for the northbound direction. After the system was installed, the distribution of vehicle speeds was statistically different, with a lower number of vehicles in the higher speed bins. Because the system was installed only recently, crash reduction impacts have not yet been evaluated. Intercept surveys of motorists at nearby rest areas revealed a positive perception of the system. Overall, the results of the evaluation indicate that the advanced curve warning system is effective.

Travelling Disturbances in the Ionosphere: Changes in Diurnal Variation

IN an earlier communication1 it was reported that the direction of horizontal movement of travelling ionospheric disturbances observed at Sydney, Australia, had a consistent diurnal variation during winter months in the years 1950–52 ; but no significant diurnal variation was then apparent in the summer. These conditions continued until 1955 ; but in the summer of 1955–56 a definite change appeared which was even more marked in 1956–57, the main feature being a marked change of direction from the south-east to the south-west quadrant about midday. The contrast is clearly evident in Fig. 1, which shows the mean diurnal variation in January for the years 1951–54 as compared with the variation for January 1957. The consistency of the results of 1951–54 is shown by the dotted lines, which indicate maximum deviation from the mean. It will be noted that the change from south-east to south-west quadrant in 1957 is quite sudden. This sequence is also found on a number of individual days, though not on all days. There was no significant change in mean speed over this time interval.