Virginia Smart Road Research Articles

Developing and Field Testing a Green Light Optimal Speed Advisory System for Buses

In this study, a Green Light Optimal Speed Advisory (GLOSA) system for buses (B-GLOSA) was developed. The proposed B-GLOSA system was implemented on diesel buses, and field tested to validate and quantify the potential real-world benefits. The developed system includes a simple and easy-to-calibrate fuel consumption model that computes instantaneous diesel bus fuel consumption rates. The bus fuel consumption model, a vehicle dynamics model, the traffic signal timings, and the relationship between vehicle speed and distance to the intersection are used to construct an optimization problem. A moving-horizon dynamic programming problem solved using the A-star algorithm is used to compute the energy-optimized vehicle trajectory through signalized intersections. The Virginia Smart Road test facility was used to conduct the field test on 30 participants. Each participant drove three scenarios, including a base case uninformed drive, an informed drive with signal timing information communicated to the driver, and an informed drive with the recommended speed computed by the B-GLOSA system. The field test investigated the performance of using the developed B-GLOSA system considering different impact factors, including road grades and red indication offsets, using a split-split-plot experimental design. The test results demonstrated that the proposed B-GLOSA system can produce smoother bus trajectories through signalized intersections, thus producing fuel consumption and travel time savings. Specifically, compared to the uninformed drive, the B-GLOSA system produces fuel and travel time savings of 22.1% and 6.1%, on average, respectively.

Evaluation of FWD Load Transfer Efficiency Measurement

This report documents an evaluation of load transfer efficiency (LTE) of dowel jointed concrete pavements. Measurement of LTE of transverse joints in concrete pavements is universally conducted using a falling weight deflectometer (FWD) device. LTE is an important parameter affecting pavement performance. Due to the importance of the results for maintenance decisions, the accuracy of the measurement technique is investigated in this report. The availability of instrumented dowel fitted concrete slabs in West Virginia Smart Road (Corridor H, Route 33 as well as Goshen Road, West Virginia) offers a unique opportunity to examine the accuracy of determining the LTE of transverse joints using FWD. For this purpose, FWD tests were conducted on both pavement sites at different times during years 2003, 2004, and 2005. Thirty transverse joints were tested along the slab edges as well as along the wheel-path. Trend analysis was performed to evaluate the effect of design features and site conditions on LTE. Key findings from this study are: (1) LTE was found to be a complex parameter that depends on many factors that include load position, testing time, slab temperature, and load transfer device. (2) Testing time and season were found to have a significant effect on the measured LTE. (3) The slabs fitted with 32 mm (1.25 in.) diameter dowels displayed higher variability of the measured LTE than those fitted with 38 mm (1.5 in.) diameter dowels. (4) Joint opening changes daily and seasonally as the ambient temperature changes. As the amount of joint opening increases due to slab contraction during winter, the measured LTE generally decreases. (5) Poor correlation was found between the deflection-based LTE and the percentage of the load transferred through the load transferring devices mounted across the transverse joint.

Quasi-static analysis of flexible pavements based on predicted frequencies using Fast Fourier Transform and Artificial Neural Network

New trend in design of flexible pavements is mechanistic-empirical approach. The first step for applying this method is analyzing the pavement structure for several times and computation of critical stresses and strains, which needs a fast analysis method with good accuracy. This paper aims to introduce a new rapid pavement analysis approach, which can consider the history of loading and rate effect. To this end, 1200 flexible pavement sections were analyzed, and equivalent frequencies (EF) were calculated using Fast Fourier Transform (FFT) method at various depths of asphalt layer. A nonlinear regression equation has been presented for determining EF at different depths of asphalt layer. For more accurate predicting of EF at low frequencies, a feed-forward Artificial Neural Network (ANN) was employed, which allows accurate prediction of EF. The frequencies obtained by the proposed regression equation and ANN were compared with frequencies observed in Virginia Smart Road project, and it was found that there is a good agreement between observed and predicted frequencies. Comparison of quasi-static analysis of flexible pavements by frequencies obtained using FFT method and full dynamic analysis by 3D-Move program approves that the critical responses of pavement computed by proposed quasi-static analysis approach are comparable to critical responses computed using full dynamic analysis.

Effect of Work Zone Lighting on Drivers’ Visual Performance and Perceptions of Glare

Nighttime crashes at work zones are major concerns for construction workers and motorists. Although in a majority of the U.S. states, department of transportation specifications for work zone lighting mention that contractors should reduce glare for workers and drivers, only two states advocate detailed specifications like light positions, orientation, and light levels. Although some studies have examined the impact of glare from work zone lights on workers and others have calculated veiling luminance levels for drivers in the work zone, the effect of work zone lighting on drivers’ visual performance and glare perception has never been studied in a realistic setting. The goal of this study was to understand the impact of commercially available portable light towers (metal halide, LED, and balloon) and their orientation on drivers’ visual performance and their perceptions of glare. Participants drove through a realistic work zone simulated on the Virginia Smart Road. Visual performance was assessed by a detection task and perception of visibility and glare were assessed by questionnaires. Results indicated that the type of light tower and its orientation affect visual performance and perceptions of visibility and glare. Light towers aimed toward the driver resulted in lowering drivers’ visual performance, both objectively and subjectively. When the light towers were aimed away from or perpendicular to the driver, the visual performance was higher and the differences in visual performance between the types of light towers were minimal. These findings indicate that these orientations should be preferred for work zone light towers.

Influence of In-Vehicle Adaptive Stop Display on Driving Behavior and Safety

In 2012, 683 000 crashes occurred at stop-sign-controlled intersections, with 2434 of those crashes being fatal and composing 5.3% of all fatal traffic incidents in the United States. Roughly 50% of all fatal crashes at stop-sign-controlled intersections involve crossing over (i.e., running) the traffic control device. With the advent of connected-vehicle technology, it is possible to provide a salient in-vehicle adaptive stop display to a driver. This display could alert a driver when he or she will have to stop at an intersection due to oncoming traffic. The same display could also permit drivers to pass through an intersection without stopping when a conflicting vehicle is not present. The purpose of this paper was to evaluate these potential improvements in safety and mobility through an empirical research study. An in-vehicle adaptive stop display was developed and tested on the Virginia Smart Road. Forty-nine drivers were exposed to multiple intersection scenarios they would experience in the real world while using connected-vehicle technology. The scenarios included variations in adjacent traffic, equipment malfunctions, and total equipment failures. There were no indications of a safety detriment to using the adaptive stop display in terms of compliance (likelihood of driver adhering to the information presented), driver complacency, or driver risk taking. Furthermore, the study indicates that, with a higher measured rate of compliance, an in-vehicle adaptive stop display would have a positive impact on safety.

Development and Preliminary Field Testing of an In-Vehicle Eco-Speed Control System in the Vicinity of Signalized Intersections

Abstract: This paper develops and addresses the implementation issues associated with the field application of an Eco-Speed Control (ESC) system that computes and recommends a fuel-efficient trajectory to drivers using signal timing and phasing data received from downstream-signalized intersections. From an algorithmic standpoint, the proposed process addresses the possible scenarios that a driver may encounter while approaching a signalized intersection. Alternatively, from an implementation standpoint the paper overcomes the challenges associated with communication latency, data errors, real-time computation, and smoothness of the drive in developing the system. The Virginia Smart Road connected vehicle controlled facility at the Virginia Tech Transportation Institute (VTTI) was used to conduct a preliminary proof-of-concept testing of the proposed ESC system. The testing included driving on downhill and uphill approaches for four red indication offset values. In total 192 trips were conducted using four different participants. The analyzed data indicate that the proposed system is very promising, producing an average reduction in fuel consumption levels and travel times in the range of 17.4 and 8.4 percent, respectively.

Evaluation of repeatability and reproducibility of continuous friction measuring equipment (CFME) using cross-correlation

Lack of sufficient friction between tyre and pavement is known to be one of the contributing factors in vehicle crashes. The application of new technologies can be used to determine the low friction areas or vulnerable accident sites at both the project and network levels. Continuous friction devices are one of the newest systems currently used in European countries that have recently been introduced to the United States. Continuous friction measuring devices are designed to measure the friction under conditions similar to those produced by an anti-lock braking system. Although continuous friction measuring equipment (CFME) provides valuable information about surface friction, processing of the relatively large amount of data produced is time-consuming. Traditional methods such as comparing the average friction provide a quick and simple data analysis method; however, they neglect other important characteristics such as friction spatial variation and low friction spots. This study proposes a methodology based on cross-correlation to compare CFME measurements. The data used in the study were collected during the annual rodeo that took place at the Virginia Smart Road. Two GripTester and one Dynatest 6875H Highway Friction Tester were used for data collection. Cross-correlation was used to synchronise the measurements. Repeatability and reproducibility of the measurements were evaluated based on the maximum cross-correlation value.

Virginia's Smart Road: Where Researchers Make the Extreme Weather

Located a couple of miles from the Virginia Tech campus in the mountains of rural southwest Virginia, the Virginia Smart Road stands as a 2.2-mile-long thoroughfare that actually goes nowhere, at l...

Short Road to Next Ride

This article discusses about the Virginia Smart Road that is frequently used by automobile researchers to test new ideas and concepts. The Virginia Smart Road is a unique, state-of-the-art, closed test-bed research facility managed by the Virginia Tech Transportation Institute and owned and maintained by the Virginia Department of Transportation. Over two-dozen major non-proprietary research projects use the Smart Road for testing in a given year. Participating organizations include heavy hitters such as car manufacturers, the Department of Transportation, the National Highway Traffic Safety Administration, and the Federal Highway Administration’s Research and Innovative Technology Administration. The Smart Road features two paved lanes and three bridges, one of which ranks, at 175 feet, as the tallest state-maintained bridge in Virginia. It also has a signalized intersection; in-pavement sensors for moisture, temperature, strain, vibration, and weighing in motion; a lighting test bed; and the half-mile-long weather-making section. Some other features include an on-site data acquisition system, a high-bandwidth fiber network, a differential global positioning system base station, and traffic signal phase and timing using remote controls.

Evaluation of the Use of Ribbed Tires for the Characterization of Skid Resistance Using Friction Models

This paper presents an evaluation of the use of ribbed tires for the characterization of skid resistance using friction models. The data used in this investigation were collected at the Surface Properties Rodeo, which was conducted on the Virginia Smart Road by members of the Virginia Consortium for Pavement Surface Properties. The paper compares measurements obtained using locked wheel testers with ribbed and smooth tires on 24 pavement sections covering a wide range of textures. Results confirmed that the International Friction Index (IFI) model is not appropriate for skid data obtained using a locked wheel tester with ribbed tires, especially when the pavement surface presents low levels of macrotexture. It was found that the friction measurements obtained when using a locked wheel tester with ribbed and smooth tires resulted in different friction–speed curves for the same pavement surface, contrary to the stated ASTM assumption that the friction–speed curve depends only on the characteristics (macrotexture) of the pavement surface. Skid measurements obtained at different speeds using ribbed tires were insensitive to pavement macrotexture. This supports the benefits of using smooth tires, which are sensitive to the drainage capacity of pavement surfaces. Finally, it is recommended that the use of the IFI model on skid data obtained using testers with ribbed tires be reassessed.

Assessment of operational characteristics of continuous friction measuring equipment (CFME)

There are many devices used around the world to measure friction. The majority of Departments of Transportation in the USA currently use locked-wheel trailers for friction measurements. The use of the fixed slip devices has gained popularity in other countries, especially in Europe, and they are starting to be used in the USA. These systems measure the friction under the condition similar to those produced by anti-lock braking system. This paper evaluates the effect of grade, water film thickness and speed on friction measurements of the continuous friction measuring equipment. The data used in this study were collected at the Virginia Smart Road using the GripTester. The experiment showed that grade affects the GripTester measurements suggesting that measuring with GripTester would be more accurate on flat surfaces. It also confirmed previous results that measurements were shown to be sensitive to water film thickness and testing speed.

Pavement macro-texture analysis using wavelets

This paper utilises a wavelet approach to interpret the macro-texture data collected on asphalt and concrete pavement surfaces with a wide range of macro-texture properties. The experimental data were obtained using a circular track meter (CTMeter) device on pavements built at the Virginia's Smart Road test facility. The size of the data-set allowed nine levels of wavelet decomposition with wavelengths ranging from 1.7 to 435 mm. The extent of macro-texture variation was summarised using the normalised wavelet energy metric defined as the sum of the squares of the detailed wavelet coefficients for the sub-bands that correspond to the macro-texture range of wavelengths divided by the length of the test section expressed in mm2/m. This metric was found highly correlated with the empirical mean profile depth measurements. Hence, the wavelet approach can be used to objectively analyse CTMeter measurements of pavement texture.

Assessment of Impact of Splash and Spray on Road Users: Results of Controlled Experiment

A preliminary field test assessed the impact of splash and spray on road users. The test was part of a larger project sponsored by FHWA to develop a model that could characterize a highway's propensity to generate splash and spray during rainfall and the impact of this on road users. “Splash and spray” refers to water thrown into the air when a vehicle tire crosses a wet surface. For the experiment, participants observed videos recorded from the driver position of a vehicle as it traveled behind another vehicle in rain conditions. The videos were recorded on the Virginia Smart Road, and the rain conditions were created with a weather-making system. The full factorial design used two levels for each of the five variables: driver vehicle, spray vehicle, maneuver, rain rate, and speed. Participants rated each video for five categories: obstruction, concentration, confidence, control, and risk. In addition, an objective measure of visual obstruction, the occlusion factor, was recorded. Several factors and interactions were found to be significant for the subjective ratings, but significance varied depending on the category being rated. The occlusion factor was found to have a strong correlation with each of the ratings, and the lowest R2 value was .75. This correlation result suggests that the occlusion factor could be used to predict user perceptions of splash and spray.

Agent-Based Stochastic Modeling of Driver Decision at Onset of Yellow Light at Signalized Intersections

This paper introduces two logistic statistical models for the driver stop–run decision at the onset of yellow at signalized intersections to capture the stochastic nature of the driver stop–run decision. One model is a classical frequentist model, whereas the other uses a Bayesian statistics approach. The Bayesian model parameters were calibrated by using the Markov Chain Monte Carlo slice procedure implemented within the MATLAB software. Both models were developed with 3,328 stop–run records, which were collected in a field experiment on the Virginia Smart Road, a limited-access highway between Blacksburg and Interstate 81 in Montgomery County, Virginia. The variables included in each model were driver gender, age, time to intersection, yellow time, approaching speed, and speed limit. Both models were shown to be consistent. For the Bayesian model application, two procedures were illustrated: cascaded regression and Cholesky decomposition. Both procedures produced replications consistent with the Bayesian model realizations, while these procedures captured the parameter correlations without the need to store the set of parameter realizations. The Bayesian model produced valid and transferable behavior by replicating multiple experimental results. The proposed Bayesian approach is ideal for modeling multiagent systems in which each agent has its own unique set of parameters.

Comparative Study of Road Profilers’ Accuracy and Precision

Abstract There is an urgent need for accurate measurement of pavement surface profile and smoothness index. This investigation compared the precision (repeatability) of the measured international roughness index (IRI) at the Virginia Smart Road for 19 profilers and their accuracy (bias) with respect to the rod-and-level reference measurement. Two existing accuracy criteria (ASTM Standard E950 and cross correlation) were compared for evaluating the relationship between the accuracy of profile elevation and IRI bias. It was found that there were profilers available that could produce the level of IRI accuracy and precision required for construction quality control and assurance. However, the accuracy and precision degraded when measuring hot-mix asphalt pavements with coarse texture and using the rod-and-level measurement as the reference. The cross-correlation method appeared to have some advantages with respect to the conventional elevation tolerance method for providing better consistency between profile accuracy and IRI bias. On the sites investigated, good cross correlation among the measured and reference profiles assured acceptable IRI accuracy.

Speed Adjustment Factors for Locked-Wheel Skid Trailer Measurements

Locked-wheel trailers are the predominant friction-testing tool used by state departments of transportation in the United States. These trailers measure friction on a locked wheel on the wetted pavement surface as the wheel slides at a constant speed. The skid resistance is reported as the skid number (SN) at the speed it was measured, with the standard test speed at 40 mph. Speed on most rural interstate and primary roads is rarely lower than 65 mph, whereas in most urban environments, congestion, intersections, and high-traffic volumes can lead to average traffic speeds as low as 20 mph. A methodology was proposed to convert the skid numbers from one speed to any desired speed by using adjustment factors. The data used to develop this methodology came from measurements taken by members of the Pavement Surface Properties Consortium for the three consecutive years from 2007 to 2009. The adjustment factors were developed for the different flexible and continuously reinforced concrete pavement surfaces that are available at the Virginia Smart Road. The friction measurements performed with the skid testers presented different responses to the different pavement surface types. To separate them, principal component analysis was used, and three different groups of surfaces were identified. Principal component analysis was also used to develop a friction conversion method that used correlations between speed and texture. Correlations between speed factors and macrotexture were computed only for smooth tire skid testers, because ribbed tires do not exhibit good relationships, probably because measurements with this tire are not sensitive to macrotexture.

Creep Behavior of Hot-Mix Asphalt due to Heavy Vehicular Tire Loading

The objective of this study is to characterize the creep behavior of hot-mix asphalt (HMA) at intermediate (20°C) and at high temperatures (40°C). To accomplish this objective, a nonlinear time-hardening creep model, characterized through laboratory testing, was incorporated into a three-dimensional (3D) finite-element (FE) model, which was used to calculate permanent creep strains after applying repetitive vehicular loading cycles at the pavement surface. Two different tire configurations were simulated representing a typical dual-tire assembly and a newly introduced wide-base tire (dual-tire: 275/80R22.5 and wide-base tire: 455/55R22.5). Results of the 3D FE model were successfully verified against pavement response measurements in the field at the Virginia Smart Road. While the elastic or linear viscoelastic FE model may not simulate permanent deformation or shear creep strains after repetitions of vehicular loading, a nonlinear time-hardening creep model could predict primary rutting damage in HMA and shear creep strains at the edge of the tire imprint caused by different tire configurations.

Evaluation of International Friction Index Coefficients for Various Devices

This paper presents a research effort to compare and harmonize measurements of texture and skid resistance taken with various devices at the Virginia Smart Road in May 2008 by the members of the Virginia Consortium for Pavement Surface Properties. There have been numerous efforts by different countries and agencies to understand better the relationship and behavior of different friction-testing devices and the influence of texture, speed, and other external conditions on these measurements. Measurements obtained with different types of equipment on 24 pavement sections with a wide range of textures were compared, and the relationship between friction and speed for the different pavement sections and devices was studied. Data were collected with two locked-wheel skid trailers, a Griptester, and a dynamic friction tester. Nine asphalt sections were tested; six were Superpave® mixes, two were stone matrix asphalt, and one was an open-graded friction course. The concrete sections tested included one continuously reinforced concrete pavement with tined finishing and two epoxy overlays. Even though all steps included in the specifications derived from the experiments by the Permanent International Association of Road Congresses (PIARC) were followed, the results obtained were not satisfactory. From a theoretical standpoint, all the values computed with the international friction index (IFI) F60 should be equal, but this was not the case. Discrepancies in the IFI values calculated for the different devices suggest that the original coefficients determined during the PIARC experiment may need to be adjusted for the devices evaluated, before the IFI can be implemented by the participating agencies.

Towards Developing an Indirect Video Visibility System for Large Trucks

Large trucks were involved in approximately 14,800 crashes between April 2001 and December 2003 as a result of making lane changes and merges (Starnes, 2006). The elimination of blind spots may help drivers avoid such conflicts by improving their spatial awareness of surrounding vehicles. This study investigated the ability of two candidate Camera/Video Imaging Systems (C/VISs) to provide information on longitudinal clearance to an adjacent vehicle. Sixteen commercial vehicle drivers performed merge maneuvers in front of an adjacent confederate vehicle while driving a tractor-trailer on the Virginia Smart Road. Both C/VIS enhancements were found to significantly improve gap judgment and merge performance. Performance differences between the two C/VIS concepts are examined.

On-Road Evaluation of an In-Vehicle Curve Warning Device

Roadway horizontal curves are the site of numerous crashes and motorist deaths each year. The objective of this study was to determine the most effective curve warning device using on-road performance and subjective evaluation. A baseline no warning condition and two multi-modal warnings were tested by 48 participants at the Virginia Smart Road closed test highway. Both warnings exhibited the same auditory (speech) and visual (Heads-Down Display) stimuli, but one also included a throttle push-back haptic stimulus. Throttle reaction times and brake reaction times were significantly quicker and curve entry speed significantly closer to an advisory speed for participants receiving a warning presentation versus those without a warning presentation. Older drivers reached more appropriate curve entry speeds than younger drivers. Driver risk-taking style was significantly related to age and curve entry speed.