Free-flow Conditions Research Articles

Approximation of the Discharge Coefficient of Radial Gates Using Metaheuristic Regression Approaches

Radial gates are widely used for agricultural water management, flood controlling, etc. The existence of methods for the calculation of the discharge coefficient (Cd) of such gates are complex and they are based on some assumptions. The development of new usable and simple models is needed for the prediction of Cd. This study investigates the viability of a metaheuristic regression method, the Gaussian Process (GP), for the determination of the discharge coefficient of radial gates. For this purpose, a total of 2536 experimental data were compiled that cover a wide range of all the effective parameters. The results of GP were compared with the Group Method of Data Handling (GMDH), Multivariate Adaptive Regression Splines (MARS), and linear and nonlinear regression models for predicting Cd of radial gates in both free-flow and submerged-flow conditions. The results revealed that the radial basis function-based GP model performed the best in free-flow condition with a Correlation Coefficient (CC) of 0.9413 and Root Mean Square Error (RMSE) of 0.0190 while the best accuracy was obtained from the Pearson VII kernel function-based GP model for the submerged flow condition with a CC of 0.9961 and RMSE of 0.0132.

Innovative Public-Private Partnership Models for Road Pricing/BRT Initiatives

This article presents alternative concepts for serving commuter travel demand in major metropolitan areas with a system of priced expressways integrated with Bus Rapid Transit (BRT), and presents potential new models for setting up public-private partnerships (PPP) to finance, implement, and operate the system. These new models may make possible the self-financing of new BRT services and facilitate efficient provision of multimodal transportation services. The PPP model for expressway operation uses shadow tolls to compensate private partners, while at the same time charging motorists market-based tolls to ensure free-flowing traffic conditions and to provide a fast, reliable running way for BRT. Revenues from tolls charged to users may be used to pay contractual obligations to private partners for highway operations, toll collection, and BRT services. To encourage efficient and effective provision of transit, high-occupancy vehicle (HOV, and park-and-ride/pool services, private partners may be compensated for provision of transit services and HOV promotion using shadow fee payments based on the number of commuters served.

Distractions by work-related activities: The impact of ride-hailing app and radio system on male taxi drivers

Use of ride-hailing mobile apps has surged and reshaped the taxi industry. These apps allow real-time taxi-customer matching of taxi dispatch system. However, there are also increasing concerns for driver distractions as a result of these ride-hailing systems. This study aims to investigate the effects of distractions by different ride-hailing systems on the driving performance of taxi drivers using the driving simulator experiment. In this investigation, fifty-one male taxi drivers were recruited. During the experiment, the road environment (urban street versus motorway), driving task (free-flow driving versus car-following), and distraction type (no distraction, auditory distraction by radio system, and visual-manual distraction by mobile app) were varied. Repeated measures ANOVA and random parameter generalized linear models were adopted to evaluate the distracted driving performance accounting for correlations among different observations of a same driver. Results indicate that distraction by mobile app impairs driving performance to a larger extent than traditional radio systems, in terms of the lateral control in the free-flow motorway condition and the speed control in the free-flow urban condition. In addition, for car-following task on urban street, compensatory behaviour (speed reduction) is more prevalent when distracted by mobile app while driving, compared to that of radio system. Additionally, no significant difference in subjective workload between distractions by mobile app and radio system were found. Several driver characteristics such as experience, driving records, and perception variables also influence driving performances. The findings are expected to facilitate the development of safer ride-hailing systems, as well as driver training and road safety policy.

New Stage–Discharge Relationship for Triangular Broad-Crested Weirs

Simple hydraulic structures, such as weirs, allow measuring flow discharge by using the upstream flow depth and a stage–discharge relationship. In this relationship, a discharge coefficient is introduced to correct all the effects neglected in the derivation (viscosity, surface tension, velocity head in the approach channel, flow turbulence, non-uniform velocity profile, and streamline curvature due to weir contraction). In this paper, the dimensional analysis and the incomplete self-similarity theory are used to investigate the outflow process of triangular broad-crested weirs, characterized by different values of the ratio between crest height p and channel width B, and to theoretically deduce a new stage–discharge relationship. A new theoretical stage–discharge relationship is suggested for the free-flow condition, and it is tested using experimental data available in the literature for the hydraulic condition p/B > 0. The obtained stage–discharge equation, characterized by low errors in discharge estimate, is useful for laboratory and field investigations. Finally, specific analysis for the triangular broad-crested weirs with p/B > 0 was developed to modify the stage–discharge relationship obtained for the case p/B = 0. This specific stage–discharge relationship allows to reduce the errors, which are generally less than ±5%, in the estimate of discharge for triangular broad-crested weirs with p/B > 0 and is also applicable for the case p/B = 0.

Evaluation of the hydraulic behavior of the composite hydraulic structure considering a bed flume with special obstacle

The experimental simulation between the composite hydraulic structure and the found obstacles in the downstream region is a challenging process due to the energy losses and kinematic dissipation. The current work focuses on a comparative analysis of free flow conditions that exist without obstacles and submerged flow conditions that occur due to obstacles. It indicates the evaluation of hydraulic variables and geometrical variables of composite hydraulic structure for both flow conditions. In addition, it includes an investigation of the interaction among these variables. The hydraulic variables include actual discharge, flow velocity, flow cross-sectional area that crosses the gate, downstream water depth, discharge coefficient, Reynolds number and, Froude number, while the vertical distance between the weir and gate represents the geometry variable. The interference between the weir discharge and gate discharge plays a significant role in the result fluctuation and variation for both flow conditions, while the form and size of the obstacles only have a major effect on the submerged flow. For both flow conditions, the water depth is investigated; there would be a drastic increase in water depth by using obstacles in the downstream area as compared with not using the obstacles. This study adopts different obstacles in shape and size, therefore, the variation of maximum and minimum water levels related to the location will occur.

Empirical analysis of impact of multi-class commercial vehicles on multi-lane highway traffic characteristics under mixed traffic conditions

The presence and movement of multi-class commercial vehicles (CVs) under different traffic conditions in a shared roadway influences the highway traffic characteristics. The purpose of this study is to quantify the impact of the varying proportion of multi-class commercial vehicles (CVs) on the speed, dynamic passenger car unit (DPCU), capacity, and level of service (LoS) of the highways through empirical analysis. The speed-flow data were collected at highway sections in India, utilizing an Infra-Red (IR) sensor device. Individual vehicle speeds are predicted using the simultaneous equations approach, which are used to determine the respective DPCU factors of the vehicles and highway capacity at different proportions of multi-class CVs. The LoS threshold values are established based on the volume to capacity (v/C) ratio for the various percentages of multi-class CVs. The study results reveal that the multi-class CVs have had a unique effect on DPCU factors of the different vehicle categories under the influence of varying proportions of multi-class CVs. The highway speed reduced by 27.76% at 30% multi-class CVs compared to 5% multi-class CVs. Eventually, the highway capacity reduced by 24.25% at 30% multi-class CVs compared to 5% multi-class CVs. The LoS varied for each highway section accordingly from free-flow condition to the congested condition due to the incremental variation in the percentage of the multi-class CVs. The study indicates that the presence of a higher proportion of multi-class CVs significantly affects the speed, DPCU, capacity, and LoS of the highways.

Numerical Modeling of the Walls Perforation Influence on the Accuracy of Wind Tunnel Experiments Using Two-Dimensional Computational Fluid Dynamics Model

The presented work is dedicated to the development of the mathematical model of a closed-type wind tunnel (WT) in a two-dimensional (2D) formulation based on the computational fluid dynamics (CFD) Unsteady Reynolds Averaged Navier Strokes Equations (URANS) method. The influence of the WT walls perforation percentage on the aerodynamic characteristics of the SC1095 (SC is an abbreviation for “supercritical”) airfoil in a wide range of pitch angles from 0 to 28 degrees has been studied. The obtained data are compared with the aerodynamic characteristics of the airfoil in free flow conditions. It is shown that the use of perforation makes it possible to significantly reduce the influence of the wind tunnel walls on the obtained aerodynamic characteristics of the airfoil bringing them closer to the airfoil characteristics under free flow conditions. The developed low resource-intensive 2D CFD WT model can be used to determine the optimal ratio between the walls perforation percentage, the WT test section dimensions, and the experimental model dimensions for various test modes. Support of WT experiments with the help of preliminary parametric studies based on the 2D CFD model could significantly reduce material costs and increase the accuracy of the obtained results.

Flow over embankment gabion weirs in free flow conditions

In this study, a series of laboratory tests were performed to investigate the effects of side ramp slope, crest length, and porous media properties on the flow regimes, water-surface profiles, discharge coefficients, and energy dissipation in embankment gabion weirs with upstream and downstream slopes. 24 physical models of solid and gabion weirs with three different upstream/downstream slopes (90°, 45° and 26.5°) were created. To investigate the complexity of flow over the porous-fluid interface and through the porous material, three-dimensional (3D) numerical simulations were developed. In numerical simulation, the standard k-ε turbulence model was utilized. A structured mesh domain was used to simulate the physical model. Water surface profiles above the porous weirs were used for comparison between the numerical simulations and measured data. These comparisons helped determine variables in the numerical simulations. Numerical simulation enables visualization of streamlines around and through the gabion weirs. In addition, mean stream wise velocity profiles above and within the porous structures were obtained. Numerical simulations showed that a reduction in the slope of the upstream face leads to an increased curvature of streamlines and the velocity distribution exhibits a non-uniform wavy shape due to the geometrical properties of the weirs. As the velocity profiles move downstream, the velocity distribution within the porous structures were more affected by the presence of the pores. The experimental results show that decreasing upstream slopes, from 90° to 26.5°, leads to decreased discharge coefficients. However, in all cases, gabion weirs lead to greater discharge coefficients than those of similar solid weirs. For milder side slopes, discharge ratios (flow passing through all faces of the gabion weirs over the inlet discharge) decreased nonlinearly. Moreover, with increasing the inlet discharge, relative energy dissipation was reduced up to 45% in gabion weirs.

How Do Individual Walk Lengths and Speeds, Together with Alighting Flow, Determine the Platform Egress Times of Train Users?

Egress times of railway passengers from train alighting up to station exit typically amount to some tens of seconds, but with much variability even at the train level. Here, we first model the egress time as the ratio of the walk length to the preferred walk speed, under free-flow conditions. Then, we model the possible occurrence of congestion among the users alighting from a train as a traffic bottleneck affecting those passing at a “queue focal point” during a “queued time interval.” Analytical formulas are provided for the CDF and PDF of egress times, covering the free-flow case and the congested case. Their computation is straightforward for bivariate Gaussian length-speed walk pair. A maximum-likelihood method is developed, together with a quick estimation procedure. A case study of four contrasted trains serving an urban mass transit station in Paris is reported. One train experienced free-flow alighting conditions, whereas each of the other three had its own bottleneck. The MLE method enabled us to recover all parameters but one, due to an issue of identifiability: the solution was to take the mean walk speed as exogenous.

IGCRRN: Improved Graph Convolution Res-Recurrent Network for spatio-temporal dependence capturing and traffic flow prediction

Accurate traffic flow prediction is critical for traffic management and route guidance, enabling urban traffic to be free-flowing conditions and maximizing transport efficiency. In current prediction methods, the simple and fixed spatial graph only uses the prior knowledge of the traffic network, resulting in weak prediction performance. This paper proposes an Improved Graph Convolution Res-Recurrent Network (IGCRRN), which relies on uncertain spatio-temporal information for traffic flow prediction. In particular, a spatial dependence matrix that combines the origin graph matrix and the data-generated embedding node matrix is created. In this way, the spatial connection relationship can be obtained from the static graph information and changing traffic flow series, making the improved graph convolution block infer and quantify the different contributions in both spatial dependence and temporal dependence in a data-driven manner. In addition, the residual structure is employed to model the multi-level spatial dependence, and the IGCRRN-cell units based on the residual connection block and LSTM are designed to make the model automatically capture the spatio-temporal dependence in the traffic flow sequence. Experiments are conducted on two real traffic datasets, and the experiment results show that our proposed spatial dependence matrix can investigate the valuable information and consider the heterogeneity in the traffic flow. The IGCRRN model outperforms the baseline and state-of-the-art methods in prediction performance.

Flow through a sluice gate over a broad crested weir under free- and submerged-flow conditions

ABSTRACT This paper describes the hydraulic characteristics of flow through a sluice gate over a broad-crested weir with a fixed upstream ramp slope of 1:2 and downstream ramp slopes of 1:2, 1:3, and 1:4. A relationship was proposed to determine the contraction coefficient of the flow passing through the gate, under free-flow conditions, in which the average value was 0.71 for all observed data. The developed relationship was used to calculate the head-loss coefficient from the studied structures under free-flow conditions, which averaged 0.31. The value of the mean absolute relative error for the proposed relationship to estimate the discharge coefficient under free-flow conditions was 1.7%. Examination of the different downstream slopes on the discharge coefficient under free-flow conditions showed that a downstream ramp slope of 1:3 is most appropriate when compared to the results for the other slopes. The value of the mean absolute relative error of the developed relationship to estimate the discharge coefficient under submerged flow conditions was 5.7%, while its corresponding value from the WinGate software was 13.1%. A survey of the effect of downstream ramp slope on the depth of submergence threshold showed that an increase in the downstream slope tends to increase the depth of the submergence threshold, whereby its value under low slopes was not significant.

Modeling driver’s braking and steering behavior along horizontal curves of two-lane rural highways for ADAS applications

Objective Drivers continuously manipulate the vehicle’s steering and pedals (throttle, brake) while driving. Inadequate or excessive manipulation leads to crashes, possibly leading to injuries. An Advanced Driving Assistance System (ADAS) can warn drivers of inadequate or excessive manipulation to avert risky situations. Such systems evolve continuously and need more road infrastructure inputs for better driving assistance. Rural highways showcased more fatalities than urban counterparts, with more road departure crashes along horizontal curves than straight sections. Hence, the present study explores drivers’ braking and steering behavior along the horizontal curves of two-lane rural highways and proposes a suitable runoff risk model. Methods Sixty-eight drivers participated in a driving simulator study, where they drove along fifty-two horizontal curves in free-flow conditions. Typical five brake and three steering measures found in past studies were evaluated. Based on data distribution of brake and steering measures, Tobit and mixed-effects multiple linear regression models were developed to understand the association of these measures with the approach speed and geometric parameters of horizontal curves. Further, a generalized linear mixed runoff (road departure) risk model with a logit link function was developed to identify the effective measures among all brake and steering variables. Results The brake and steering measures were significantly associated with the approach speed and the geometric parameters such as curve radius, gradient, and turn type (left or right). Further, the runoff risk analysis revealed a significant effect of braking distance (BD) and standard deviation of steering wheel position (SDSWP). The interaction between BD and SDSWP was significant, suggesting that the runoff risk increased with SDSWP; however, it decreased with BD. Conclusions The runoff risk intensified with higher steering instability along horizontal curves, while it can be reduced with effective brake pedal usage. The study suggests better usage of brakes than steering before entering the curve. It potentially reduces the vehicle speed, thus ensuring more time to perceive the curve and help reduce the driver’s steering instability. The models developed in this study can be used in the ADAS systems upon validation with the field observations.

Mode differentiation in partitioning of mixed bi-modal urban networks

ABSTRACT Empirical studies have demonstrated the existence of a well-defined Network Macroscopic Fundamental Diagram (NMFD). Well-shaped NMFD, however, may not be a universal law because urban networks often display heterogeneous congestion distributions. Therefore, different algorithms have been proposed to partition a heterogeneous network into homogeneous sub-networks. These algorithms mainly consider uni-modal networks, despite the multi-modal nature of urban traffic flows. This paper is one of the first studies dedicated to the partitioning problem of bi-modal networks. First, a three-step partitioning algorithm is developed concerning NMFD-based applications. Second, the role played by mode differentiation in bi-modal network partitioning is investigated through the lens of speed-NMFDs. The results demonstrate that the algorithm performs well. Mode differentiation should be considered in the partitioning process while is defined differently in free-flow and saturated conditions. The links' lengths, bus stop distribution, speed limit zone, and the existence of bus terminals might affect speed-NMFD properties.

Correct path to use flumes in water resources management

The hydraulic characteristics of the flow are measured using tools such as flumes, in the design and evaluation of furrow irrigation systems. Proper use of these tools, such as their immersion while working, is one of the important executive points in this field; in this study, trapezoidal flumes are used to measure the intensity of input and output flow in furrow irrigation. The proper method of installing these flumes was investigated in this article. For this purpose, during 60 irrigation operations, the results showed that in order to create free flow conditions in these flumes, and not to affect the downstream and upstream current, as well as increasing the accuracy of measurements, in addition to installing flumes in all directions, trapezoidal flume should be installed at a height of at least about 4 cm above the furrow bed; according to the irrigation operations, the percentage of immersion in the installation of the flume at a height of 4 cm from the furrow bed was observed as standard (less than 70% immersion) in order to reduce the percentage of flow measurement error in different depths of water entering the flume. The results also showed that for ensuring free flow in trapezoidal flumes, the flume should be installed at a height of 4 cm or more above the furrow bed, provided the input ridges are strengthened and the end flume is measured to measure the inflow to the furrow. The output current of the furrow should be installed in the floor of the furrow along the bed to prevent the passage of current, provided that after the outflow flume, the furrow bed should be deeper in terms of free flow. Observance of the points and results obtained in this study in furrow irrigation systems prevents errors in flow measurement and consequently increases the accuracy in the design and evaluation of furrow irrigation systems.

Rheology of particulate suspensions with non-Newtonian fluids in capillaries.

Particulate suspensions occur in situations from blood flow to slurries in drilling applications. Existing investigations of these suspensions generally concentrate on the impact of particle volume fraction for suspensions in Newtonian fluids under free-flow conditions. Recently, particulate-polymer composites have been used in additive manufacturing (AM). Here, the polymer becomes a shear-thinning non-Newtonian fluid during extrusion, creating a particulate suspension. Motivated by the challenges in AM of particulate composites, this study investigates the rheology of suspensions of micrometre-sized particles in shear-thinning silicone while extruded through AM-scaled nozzles (millimetre-scale diameters). The suspensions were observed to follow a power-law behaviour and their rheology was investigated through the measured flow consistency () and behaviour () indices. The impact of the particle volume fraction () and the ratio () of the capillary inside diameter to the particle diameter on both indices were measured. was found to be only impacted by the suspension fluid type and . was found to be constant at large , but decreased and then increased to infinity with decreasing. Based on its behaviour, was categorized into two conditions and analysed separately with semi-empirical models. The impact of particle size distribution was also investigated.

Bridge Construction. An Economical and Sustainable Approach

This paper presents a methodology that quantifies the life cycle costs of concrete decks of roadway bridges that supports the decision-making regarding the optimal selection between several construction / repair alternatives. A deterioration model based on the main material and environmental characteristics of bridges is presented. Some of the most up-to-date materials that are used on concrete bridges are also presented and characterized. The quantification of the user costs is presented. These calculations are made considering the vehicle operating costs, the cost of time and accident costs. The user costs are determined by comparing the traffic costs under free flow conditions with those that arise from disrupting the free traffic flow. The created model is applied to an existing bridge, where the determination and comparison of the costs of the application of different repair alternatives are analysed. At the end, the main conclusions and recommendations are presented.

A comparative study on the accuracy and conservation properties of the SPH method for fluid flow interaction with porous media

Smoothed Particle Hydrodynamics (SPH) has successfully been employed in the last decade for macroscopic simulation of fluid flow in porous media. However, there are still certain inconsistencies in the existing models with regard to both the definition of the governing equations and the adopted numerical treatments. In this study, thus, in order for a comparative investigation of the existing practices, the method of spatial averaging is employed to derive two types of macroscopic conservation equations of mass and momentum through phase averaging and intrinsic phase averaging of fluid density. Consistent discretisation methods are adopted for the determination of particle's volume, in the Weakly Compressible SPH form, and velocity by which particles move; and they are used to construct three numerical models. The models are then employed to solve two different types of problems: i) a fully saturated soil medium under the closed channel flow condition, and ii) a porous medium under a free surface flow condition with varying saturation. The results of the models are compared with analytical and experimental data; and particle distribution, water surface elevation, conservation of fluid volume, and pressure distribution are investigated. It is shown that only the latter type of modelling (i.e., intrinsic phase averaging of fluid density) leads to the conservation of fluid volume for both types of the problems, while the former type of formulation (i.e., based on phased averaged density, also known as apparent density) is suitable for closed porous media flow conditions only. Comparisons with other numerical models and the author's previous study indicate that the adopted numerical treatments, especially the δ-SPH formulation, have led to an improvement in the smoothness of particles distribution and pressure field. A few recommendations are finally made about potential further improvements of the developed models and extensions of their applicability.

The Effect of Amiloride (10mg) on the Blood Pressure Response to Ischemic Exercise: Preliminary Observations

BackgroundDuring exercise, blood pressure increases via augmented central command and stimulation of mechano‐ and metabosensitive muscle afferents (i.e., the exercise pressor reflex). Recent evidence has reported a strong role of acid sensing ion channels (ASIC’s) in mediating this reflex, as well as exercise induced muscle pain. Therefore, it is logical to suspect that inhibiting ASIC’s would mitigate the exaggerated blood pressure responses and exercise related muscle pain observed in individuals with peripheral artery disease (PAD).Purpose. We tested the hypothesis that a single 10mg dose of amiloride (a K+‐sparing diuretic known to inhibit ASIC’s) would attenuate the pressor response to blood flow restricted (BFR) plantar flexion exercise in young healthy adults.MethodsSix healthy subjects (5 male, 26 ± 2 y/o, 180.8 ± 12.1 cm, 79.7 ± 12.9 Kg) completed three separate visits. Each visit included two bouts of isometric plantar flexion, both performed until failure at 30% of the predetermined maximal voluntary isometric contraction. During one bout, blood flow to the limb was restricted via a pressurized cuff placed around the proximal portion of the lower leg (BFR); the other bout was performed under free flow conditions. In the first visit, subjects performed these two exercise bouts (in random order) under normal, non‐treated conditions. In the second and third visits, subjects performed these exercise bouts (same order as in visit 1) ~3 hrs after oral ingestion of 10mg of amiloride, or ingestion of a placebo (random order). Blood pressure and heart rate were continuously recorded throughout exercise, and time to fatigue and muscle pain (on a 12cm visual analog scale) was recorded at the end of each exercise bout. Only data from the placebo and amiloride conditions are presented here.ResultsThe addition of BFR reduced total exercise time by ~40.8% (t=2.99, p=0.03), but had no significant effect on peak muscle pain (p>0.10). Due to the preliminary nature of these data, no significant main effects of treatment (amiloride vs. placebo) were observed for free flow or BFR exercise (all p>0.05). However, we did observe a net decrease in the average heart rate response (+10.7 ± 3.0 bpm vs. +11.3 ± 3.7 bpm, ηp2=0.539, p>0.47), the total blood pressure response (5477.5 ± 373.7 mmHg*sec vs. 5841.3 ± 518.9 mmHg*sec, ηp2=0.250, p>0.30), the total time‐tension index (595.9 ± 406.5 Kg*sec vs. 691.6 ± 394.2 Kg*sec, ηp2=0.211, p>0.30), and the blood pressure to time‐tension index relationship (9.09 ± 4.40 mmHg/Kg vs. 11.38 ± 6.30 mmHg/Kg, ηp2=0.08, p>0.50) in the amiloride condition compared to the placebo condition during BFR exercise.ConclusionsWhile these preliminary findings do not indicate significant effects of treatment, these observations serve as strong pilot data to support the continued investigation of amiloride as a method of attenuating the pressor response to ischemic exercise.

A NIRS‐derived Skeletal Muscle Oxygen Consumption Method Accurately Reflects the Gold Standard Direct Fick Method during Single‐leg Knee Extension Exercise

BackgroundQuantifying the oxygen consumption (V̇O2) of skeletal muscle, which represents the largest metabolically‐active tissue mass, is an important assessment in exercise physiology. The gold standard for quantifying muscle V̇O2 in the exercising human is the direct Fick method, however, technical challenges (e.g. arterial catheter insertion) preclude the widespread use of this technique, justifying the need for alternative approaches for the quantification of muscle V̇O2. Recently, we developed a noninvasive method of quantifying muscle V̇O2 using Doppler ultrasound measurements of blood flow (Q̇) and near‐infrared spectroscopy (NIRS)‐derived deoxygenated‐[Heme] in a modified Fick method calculation, but, to date, this has not been validated against the gold standard method.Purpose and HypothesesTherefore, the purpose of this investigation was to compare NIRS‐derived and direct Fick quantification of muscle V̇O2 at multiple levels of single‐leg knee‐extensor exercise. We tested the hypotheses that: 1) the muscle V̇O2 assessed by direct Fick and the NIRS‐derived muscle V̇O2 would not be statistically different from each other across work rates, and 2) the V̇O2 assessed by the two techniques would be strongly related.MethodsSeven healthy young volunteers (3 women, 4 men; 24 ± 5 years) performed an incremental work rate test on a dynamic single‐leg knee‐extensor ergometer. Measurements of femoral artery Q̇ (Doppler ultrasound), vastus lateralis deoxygenated‐[Heme] (NIRS), and femoral artery and vein oxygen content were taken at rest, 0, 5, 10, 15, and 20 Watts (W) and used to estimate direct Fick and NIRS‐derived muscle V̇O­2.ResultsNIRS‐derived V̇O2 was not different from direct Fick V̇O2 at any point (rest: 45 ± 21 vs 25 ± 17 ml/min; 0 W: 153 ± 70 vs 133 ± 68 ml/min; 5 W: 188 ± 81 vs 160 ± 65 ml/min; 10 W: 242 ± 123 vs 214 ± 91 ml/min; 15 W: 279 ± 131 vs 247 ± 89 ml/min; 20 W: 343 ± 163 vs 319 ± 122 ml/min; all P = 0.26 – 0.44). Muscle V̇O2determined by the two techniques was strongly related (r2: 0.97 ± 0.03) with a slope of 1.1 ± 0.3 and Y‐intercept of ‐21 ± 22 ml/min.DiscussionTaken together, these findings indicate that the NIRS‐derived, noninvasive assessment of skeletal muscle V̇O2 accurately reflects the gold standard quantification of muscle V̇O2over a range of work rates (with a constant ≍20 ml/min offset). This investigation provides the first evidence to support the use of the NIRS‐derived muscle V̇O2 estimate during free‐flow conditions (i.e. not using venous or arterial occlusions like previous work), introducing a novel, noninvasive technique to quantify exercising skeletal muscle V̇O2.

Placement Distance of Exit Advance Guide Sign on an Eight-Lane Expressway Considering Lane Changing Behavior in China

The reasonable placement of the advance guide signs (AGSs) is important in improving driving efficiency and safety when exiting an expressway. By analysing the lane-changing process when approaching an exit on new two-way eight-lane expressways, we modified the tradi-tional AGS model lane-change distance formula. To this end, a field experiment was designed to explore the lane-change traversal time at the free flow condition (LOS 1). Considering the limitations of the experimental equip-ment, lane change distance at the worst levels of service was explored using VISSIM simulation. The results show that the eight-lane changing distance based on modified theoretical calculations, revealed a minor difference with VISSIM simulation in free flow condition. Further-more, placement distance at the worst levels of service are discussed. Then placement distance of all-level AGSs is recommended to be 3 km, 2 km, 1.2 km, and 0.8 km, considering the driver's short-term memory attenuation calculation formula. Determining the two-way eight-lane AGS placement distance from the perspective of LOS can provide a basis on which to supplement the existing stan-dards and references for the AGS placement distance af-ter the expressway expansion in China.