bluuebunny/crossref_metadata_2025 huggingface dataset:
Duration of Spring Thaw Recovery for Aggregate-Surfaced Roads
Authors: Embacher Rebecca A.
Published: May 2018

Low-volume roads in regions susceptible to freezing and thawing periods are often at risk of load-related damage during the spring thaw. Reduced support capacity during this period results from excess melt water that becomes trapped above underlying frozen layers. Many agencies place spring load restrictions (SLRs) during the thaw period to reduce damage to roadways. The period of SLRs set forth by the Minnesota Department of Transportation is effective for all flexible pavements; however, experience suggests that many aggregate-surfaced roads require additional time relative to flexible pavements to recover strength sufficient to carry unrestricted loads. An investigation was performed to improve local agencies’ abilities to evaluate the duration of SLR on aggregate-surfaced roadways. This was accomplished through seasonal measurements of in situ shear strengths, measured with the dynamic cone penetrometer, on various Minnesota county routes. In situ strength tests were conducted on selected county gravel roads over the course of 3 years. Strength levels recorded during the thaw-weakened period were compared with fully recovered periods that typically occur in late spring or summer. Results indicate that aggregate-surfaced roads generally require 1 to 3 additional weeks over that required by flexible pavements to reach recovered bearing capacity.
Safety and Cost-Effectiveness of Approach Guardrail for Bridges on Low-Volume Roads
Authors: Gates Tim J. , Noyce David A. , Stine Paul H.
Published: May 2018

The bridge approach guardrail is a commonly used safety feature designed to prevent collisions with bridge components and other types of run-off-the-road crashes occurring on the approach or departure to bridges. The average daily traffic (ADT) threshold at which an installation of bridge approach guardrail on low-volume roads is cost-effective was determined on the basis of reductions in crash severity. Logistic regression and chi-squared tests were used to analyze characteristics of 96 run-off-the-road crashes that occurred on the approach or departure to 68 county state-aid highway bridges in 10 Minnesota counties over a 15-year period. Crashes that occurred at bridges with approach guardrail were found to be significantly less severe than crashes that occurred at bridges without guardrails. None of the 33 crashes with approach guardrail resulted in a fatality or severe injury, whereas roughly one-quarter of the 63 crashes with a roadside or bridge rail end resulted in a fatality or severe injury. Crashes with the approach guardrail were much more likely to result in property damage only compared with crashes with the roadside or bridge rail end. Bridge approach guardrail installed at all four quadrants of a bridge has a benefit–cost ratio ranging from 3.99 to 6.62 and is cost-effective at ADTs greater than or equal to 400. An ADT threshold of 400 is recommended for installation of a bridge approach guardrail on low-volume roads; this is consistent with current roadside clear zone guidelines suggested by AASHTO for very low-volume local roads.
Laboratory Evaluation of Untreated and Treated Pavement Base Materials
Authors: Mohammad Louay N. , Herath Ananda , Rasoulian Masood , Zhongjie Zhang
Published: May 2018

Pavement performance is related to resilient modulus and permanent deformation properties of pavement materials, as well as other factors such as environmental and traffic conditions. Current resilient modulus test procedures and correlations do not fully describe permanent deformation properties. This limitation signifies the need for a permanent deformation test procedure for proper material characterization. The objective of this study was to evaluate resilient and permanent deformation properties of seven base materials with a proposed permanent deformation test that can provide both resilient modulus and permanent deformation properties. The base materials used were obtained from test sections recently constructed at the Louisiana Pavement Research Facility. These included crushed limestone, blended calcium sulfate, blended calcium sulfate treated with slag, blended calcium sulfate treated with fly ash, recycled asphalt pavement, foamed asphalt–treated 100% recycled asphalt pavement, and foamed asphalt–treated blend of 50% recycled asphalt pavement and 50% soil cement. Laboratory repeated load triaxial permanent deformation and material property tests were performed on these materials. A power model that correlated the accumulated permanent strain to the number of repeated load cycles for each material considered was developed. A good correlation between resilient moduli and permanent strains was observed. Blended calcium sulfate treated with slag exhibited the highest resilient modulus and the lowest permanent deformation values of the investigated materials, followed by blended calcium sulfate treated with fly ash, blended calcium sulfate, crushed limestone, and recycled asphalt pavement.
Evaluation of Resilient Modulus Model Parameters for Mechanistic–Empirical Pavement Design
Authors: Elias Mohammed B. , Titi Hani H.
Published: May 2018

Correlations were developed to estimate the resilient modulus of various Wisconsin subgrade soils from basic soil properties. A laboratory testing program was conducted on common subgrade soils to evaluate their physical and compaction properties. The resilient modulus of the investigated soils was determined from repeated load triaxial testing according to the AASHTO T 307 procedure. The laboratory testing program produced consistent results and a high-quality database. The resilient modulus constitutive equation adopted by NCHRP Project 1–37A was selected for this study. Comprehensive statistical analysis was performed to develop correlations between basic soil properties and the resilient modulus model parameters ki. The analysis did not yield good results when the whole test database was used. However, good results were obtained when fine-grained and coarse-grained soils were analyzed separately. The correlations developed were able to estimate the resilient modulus of the compacted subgrade soils with reasonable accuracy. To inspect the performance of the models developed in this study, comparison with the models developed on the basis of the Long-Term Pavement Performance (LTPP) database was made. The LTPP models did not yield good results compared with the models proposed by this study because of differences in the test procedures, test equipment, sample preparation, and other conditions involved with development of both LTPP and the models of this study.
Design Model for Roughness and Serviceability of Pavements on Expansive Soils
Authors: Hong Gyeong Taek , Bulut Rifat , Aubeny Charles P. , Jayatilaka Ranashinghege , Lytton Robert L.
Published: May 2018

A model was developed to predict pavement roughness caused by both expansive soils and traffic in terms of the serviceability index (SI) and the International Roughness Index (IRI). The model correlates the roughness analysis to the vertical movement estimated from the Texas A&M University suction-based method. The total vertical movement (including both swelling and shrinking) at the edge of pavement sections, the geometry of the pavement, site conditions, traffic, and the level of reliability were used as model parameters. Total movements calculated at the edge of pavement sections were based on a relationship between moisture content and suction, exponential suction envelopes, volume change coefficients, pavement treatments, and roadside conditions. Pavement treatments included vertical and horizontal barriers, inert soil, and lime-stabilized or cement-stabilized layers. The movements in wheelpaths at a distance from the edge of pavement were estimated on the basis of both field observations and the computed results of a transient finite element analysis. Transverse distribution of vertical movements on a pavement cross section was estimated. A relationship between IRI and SI was developed on the basis of surface profile measurements in several pavement study sections. The design equations that were developed for both flexible and rigid pavements include the effects of traffic and expansive soil and permit the selection of the desired level of reliability.
Estimation of Expected Moisture Contents for Pavements by Environmental and Soil Characteristics
Authors: Oh Jeongho , Ryu Duchwan , Fernando Emmanuel G. , Lytton Robert L.
Published: May 2018

Expected moisture contents were evaluated for pavements on the basis of climatic and soil characteristics with the use of the Enhanced Integrated Climatic Model (EICM). Subgrade moisture content varies with environmental and soil conditions and has significant influence on pavement performance. Thus, it is important to establish realistic estimates of expected subgrade moisture contents to account for the effects of this variable on predicted pavement performance during the design stage properly. To predict expected moisture contents, researchers examined regional variations in climatic and soil–water characteristic curves in Texas. Through cluster analysis, seven climatic and nine soil regions were established that captured the variations in climatic and soil characteristics across the state. Typical pavement structures and groundwater table data in different regions were used to reflect regional characteristics and to estimate the initial boundary soil suction profile for a given pavement, which is a critical factor in determining expected moisture variations in the subgrade for given pavement and climatic and soil conditions. The limited verification of the EICM analysis showed realistic predictions of moisture contents when compared with field measurements and confirmed that the results of the regional characterizations are reasonable. Accordingly, researchers evaluated the expected moisture variations across different regions. The results indicate that in most pavements the predicted moisture contents reach an equilibrium stage at some time after construction. From these results, researchers established expected moisture contents that reflect the variation in environmental and soil characteristics across Texas.
Asphalt Multi-Integrated Rollers and Steel Drum Compactors
Authors: Abd El Halim Abd El Halim Omar , Mostafa Abdelzaher
Published: May 2018

Theoretical analysis supported by laboratory investigations and verified by field studies and observations has shown that defects caused by rolling compaction are the main contributors to early deterioration of asphalt surfaces. The conventional and widely used steel drum roller induces hairline cracks, which permit moisture to infiltrate pavement structure, causing the phenomenon known as stripping. In addition to inducing cracks, steel drums do not provide the desired uniformity in terms of density across the compacted width of the asphalt mat. Drummed rollers also produce poor compaction at unsupported edges of paved lanes. The asphalt multi-integrated roller (AMIR), an innovative compaction technology, offers a more effective alternative for overcoming problems of steel drum rollers by reducing permeability and, in turn, improving long-term performance of flexible pavements. A multistaged laboratory and field-testing program that measures permeability in terms of hydraulic conductivity was performed on pavement sections constructed using an AMIR side by side with a conventional steel roller. Asphalt concrete layers compacted by steel drum rollers were found, on average, to be up to 20 times more permeable than those compacted by the AMIR immediately after construction and as much as 10 times more permeable after 1 year. The major steps leading to the understanding of how rolling affects the permeability of asphalt layers and, consequently, the long-term performance of newly compacted pavements are discussed and presented.
Travel Time Estimation with Correlation Analysis of Single Loop Detector Data
Authors: Guo Huairui , Jin Jionghua (Judy)
Published: May 2018

In this paper, the average travel time over a link is considered as a random variable following an identical probability distribution as the arrival process. A new estimation method of the average travel time uses a cross-correlation analysis of traffic flow measurement data. This method requires only traffic flow information, which is available from the measurements of single loop detectors upstream and downstream from one link. Different from the existing maximum cross-correlation analysis method, the proposed method considers average travel time as a random variable, with its mean value estimated from all significant cross-correlation coefficients rather than from only the maximum cross-correlation coefficient. Therefore, the inherent variability of average travel time among different vehicles can be considered. Moreover, different from the existing optimization method, the proposed method uses the statistical t-test of the significant cross-correlation coefficients to determine automatically and adaptively the fitting range of the probability density function of the average travel time. Thus, it avoids using the approximated car length factor and has no need to predetermine the range of the average travel time as required by the optimization method. Details of the average travel time estimation procedures are presented, and the effectiveness of the proposed method is demonstrated through both simulation study and a case study of real traffic data.
Predicting Directional Design Hourly Volume from Statutory Holiday Traffic
Authors: Liu Zhaobin , Sharma Satish
Published: May 2018

Estimating design hourly volume (DHV)—commonly the 30th highest hourly volume (30HV) in a year—from sample counts is an important aspect of traffic engineering practice. Directional DHV (DDHV) on highways without permanent traffic counters (PTCs) is usually determined by the estimated annual average daily traffic (AADT) being multiplied by the ratio of DHV to AADT and the directional split ratio during the DHV at a PTC on a similar road. However, highway designers have questioned the validity of this method, and its limitations have been well discussed. Because recreational travel on most holidays in developed countries is active and increases highway traffic volumes vastly, the main intent is to develop more accurate and efficient DDHV prediction models based on directional hourly volumes that occur during holiday periods. The existing literature on DHV is reviewed, then holiday traffic peaking characteristics are investigated on the basis of the past 20 years of data from PTCs on rural highways in Alberta, Canada. Accounting for holiday traffic peaking characteristics such as directional peaking features, discernible and consistent hourly volume patterns during holiday weeks, and the remarkable contributions of holiday travel to the yearly highest hourly volumes, genetic algorithms (GAs) are used to assist in the development of several DDHV prediction models that correspond to various holidays and road types. The analysis results indicate that GA-assisted DDHV models consistently outperform the existing models.
Forecasting Shared-Use Vehicle Trips with Neural Networks and Support Vector Machines
Authors: Cheu Ruey Long , Xu Jianxin , Kek Alvina G. H. , Lim Wei Ping , Chen Way Ling
Published: May 2018

Two trip-forecasting approaches—neural networks and support vector machines—are compared for a multiple-station shared-use vehicle system. The neural networks trained to perform trip forecasting belong to the multilayer perceptron model. Comparative evaluation was made with least-squares support vector machines with the radial basis kernel function. The forecasting models were trained or developed for 6 months, then validated with 1 month of actual trip data from the Honda Intelligent Community Vehicle System, currently in commercial operation in Singapore. Each model was designed to forecast the net flow of vehicles for a 3-h period on any day in a month at a particular shared-use vehicle port. The models were developed for and applied to forecasting the net flow at each port for each entire month from January 2004 to June 2004. Results indicate that the multilayer perceptron model has a slightly better forecast accuracy in terms of monthly average absolute error and monthly maximum absolute error.
Performance Evaluation of Sensor- and Image-Based Technologies for Automated Pavement Condition Surveys
Authors: Capuruço Renato A. C. , Tighe Susan L. , Ningyuan Li , Kazmierowski Tom
Published: May 2018

Even though companies that assess pavement condition compete to innovate by providing better software for automatic analysis and diagnosis, the industry as a whole remains limited, and data collection and storage methods are disparate. In fact, software and handling procedures are proprietary—each vendor has its own automated technology to detect, classify, and quantify surface distresses. In a research effort sponsored by the Ministry of Transportation of Ontario, Canada, the performance of sensor- and image-based pavement condition assessment was compared. First, a data management plan was created to allow efficient data manipulation. Second, a suitable set of similar distresses was selected as response variables of interest to design and conduct statistical experiments. Third, advanced analysis of variance was performed to allow statistical data comparisons among companies and among automated technologies. Finally, results were discussed and recommendations made. Overall, service provider measurements using sensor-based equipment showed no significant differences; however, those taken with digital image technology did. The implications of such outcomes, including implementation details to encourage practitioners to benefit from these preliminary results, are discussed. More broadly, road agencies are given an opportunity to revisit selection decisions concerning the acceptance or rejection of pavement data collected by a range of contractors.
Frameworks to Represent Uncertainty when Level of Service is Determined
Authors: Kikuchi Shinya , Chakroborty Partha
Published: May 2018

The introduction of the concept of level of service (LOS) and the process to measure it are important contributions of the Highway Capacity Man ual(HCM). Recently, the usefulness and validity of the LOS categories have been reexamined. One underlying issue is how to handle uncertainty embedded in the definition of LOS, measurement of the flow condition, and matching the measured condition with the LOS categories. HCM suggests the “use of judgment” to handle uncertainty. The aspects of uncertainty involved in LOS analysis are examined, and different approaches to quantify the uncertainty, depending on its nature, are suggested. The truth of the statement “flow condition Xis LOS = Z” is determined by a deterministic, probabilistic, or possibilistic framework, depending on the character of Xand Z For varying combinations of Xand Z, different frames of analysis must be used. Six combinations of types of Xand Zare identified. One extreme is when both X and Zare assumed to be precise; such is the current HCM practice. The other extreme is when the boundaries of Z and X are assumed to be vague. Between these two extremes, four cases are identified, and an appropriate analytical framework is suggested for each. Results indicate that the aspects of uncertainty should be understood and that the mathematical framework selected for analysis should be consistent with the types of uncertainty involved.
Applications of Artificial Intelligence Paradigms to Decision Support in Real-Time Traffic Management
Authors: Chowdhury Mashrur , Sadek Adel , Ma Yongchang , Kanhere Neeraj , Bhavsar Parth
Published: May 2018

Decision support for real-time traffic management is a critical component for the success of intelligent transportation systems. Theoretically, microscopic simulation models can be used to evaluate traffic management strategies in real time before a course of action is recommended. However, the problem is that the strategies would have to be evaluated in real time; this might not be computationally feasible for large-scale networks and complex simulation models. To address this problem, two artificial intelligence (AI) paradigms—support vector regression (SVR) and case-based reasoning (CBR)—are presented as alternatives to the simulation models as a decision support tool. Specifically, prototype SVR and CBR decision support tools are developed and used to evaluate the likely impacts of implementing diversion strategies in response to incidents on a highway network in Anderson, South Carolina. The performances of the two prototypes are then evaluated by a comparison of their predictions of traffic conditions with those obtained from VISSIM, a microscopic simulation model. Although the prototype systems’ predictions were comparable to those obtained by simulation, their run times were only fractions of the time required by the simulation model. Moreover, SVR performance is superior to that of CBR for most cases considered. The study results provide motivation for consideration of the proposed AI paradigms as potential decision support tools for real-time transportation management applications.
Moments Analysis for Improving Decision Reliability Based on Travel Time
Authors: Lu Jiangang , Yang Fan , Ban Xuegang , Ran Bin
Published: May 2018

Decision reliability is becoming an important issue for both researchers and transportation service providers; different models and methods have been proposed to improve decision reliability. A method is proposed for improving decision reliability by analyzing the moments and central moments of historical travel time data. Because of the existence of traffic congestion—especially nonrecurrent traffic congestion—travel time is generally a random variable with an asymmetric historical distribution. Statistical methods are applied to obtain the higher-order moments and central moments of historical travel time, which provide quantitative information about the variability, asymmetry, and leptokurtosis of travel time. This information is useful in making reliable decisions and avoiding scenarios that can potentially lead to extremely high costs. The method is based on advanced traveler information systems, which provide useful historical travel time information for traffic networks. The new method and other methods are compared with two testing experiments.
Unscented Kalman Filter Method for Speed Estimation Using Single Loop Detector Data
Authors: Ye Zhirui , Zhang Yunlong , Middleton Dan R.
Published: May 2018

The accurate estimation of flow speeds with single loop data is critical to freeway traffic management. Many existing methods cannot accurately estimate speed because of difficulty in determining vehicle lengths and because some assumptions can be applied only to certain limited conditions. Moreover, excessive experimentally determined parameters some proposed approaches difficult to implement. A new unscented Kalman filter method of speed estimation is presented. The algorithm of the proposed method is implemented and evaluated with the use of field data from Texas Transportation Institute's vehicle detector test beds on State Route 6 in College Station, Texas, and on Interstate 35 in Austin, Texas. Estimated speeds are compared with observed speed data and with results from other estimation methods. The results indicate that the proposed method has excellent estimation accuracy and outperforms other methods. In addition to its superior accuracy, the proposed method is fairly easy to implement and practical for real-system implementation.
Analysis of Speeding in Saudi Arabia and Effectiveness of Enforcement Methods
Authors: Al-Ghamdi Ali S.
Published: May 2018

The current study tackles three aspects of the speeding problem. First, the magnitude of the problem for driver compliance is assessed by a comparison of the 85th percentile speed with the posted speed limit. The second aspect deals with selected speed limits at study sites, and models for estimating these percentiles are suggested. Examining the effect of automated speed enforcement with speed radar cameras and the presence of police cars was the third aspect. A sample of slightly more than 69,000 spot-speed observations was gathered from 41 sites (14 freeways, 22 arterials, and 5 residential streets) during 2003 in Riyadh, the capital of Saudi Arabia, and in Buraidah, a small city about 300 km north of Riyadh. Analysis showed that the study sites were suffering from a tremendous speed problem. Although the problem could be blamed in part on inappropriate selection of speed limits, the speeding trends disclosed that drivers overall tend to exceed the posted limit by a great amount. The proportions of motorists with 85th percentile speeds over the speed limit are 10%, 88%, and 100% on freeways, arterials, and residential streets, respectively. A primary concern is the relatively high speeds observed on residential streets. Although the speed limit on such streets does not exceed 40 km/h, the observed 85th percentiles were all more than 55 km/h; this highlights the speeding issue on these neighborhood streets, where pedestrian activities are prevalent. The study found that both enforcement methods, namely, speed radar cameras and police car presence, appeared effective and led to a reduction of mean speed by at least 10 km/h.
Reasonable Speed Limits on Suburban Multilane Highways with Curbs
Authors: Baek Jongdae , Hummer Joseph E. , Williams Billy M. , Cunningham Christopher M.
Published: May 2018

When some two-lane roads with 55 mph speed limits are widened to four through lanes, curb and gutter is installed to address issues such as access control, difficult terrain, and limited right-of-way. Posted speed limits along such highway segments are typically decreased to 45 mph in North Carolina because of guidance in the AASHTO Green Book and elsewhere that vertical curbs should not be placed next to high-speed lanes. Although much money is spent to improve such roadways, the results may be viewed negatively by the public, design professionals, and law enforcement personnel. Drivers may be unhappy about getting tickets or driving more slowly, designers are unhappy about being blamed by the public, and police are unhappy about the increased enforcement burden. To help resolve such a dilemma, in this research the team collected relevant data such as speeds and collisions on four-lane road sections with curbs that have 45 or 55 mph speed limits and nontraversable medians or two-way left-turn lanes. The team found that the speed limit does not seem to make an important difference in collision rates or severities for the roads the team examined. The higher speed limit also made relatively small differences in the mean speeds and speed variances observed. Considering all results, the researchers recommended that the North Carolina Department of Transportation continue its current policy of allowing 55 mph speed limits on four-lane roads with curbs on a selective, case-by-case basis.
Safety Impacts of Photo-Red Enforcement at Suburban Signalized Intersections
Authors: Miller John S. , Khandelwal Rahul , Garber Nicholas J.
Published: May 2018

Photo-red enforcement entails cameras that photograph a vehicle entering an intersection after the traffic signal has turned red; a citation is then mailed to the vehicle's owner. Such a program was operated at 13 signals in Fairfax County, Virginia, between 2000 and 2005. This paper reports how photo-red enforcement affected crash frequency at the intersections. An empirical Bayes approach was used to detect the impact of the program on crashes while main-line traffic volume, yellow time, truck percentage, number of left-turning lanes, and speed limit were controlled. Cameras were definitely correlated with decreased red light running crashes (11% to 55%), increased rear-end crashes (32% to 85%), increased total crashes (0% to 23%), and decreased red light running injury crashes (5% to 64%). Cameras were probably associated with increased total injury crashes (5% drop to a 33% raise). These results are consistent with those of other studies with one notable exception: In the case of Fairfax County, the magnitude of the increase in rear-end crashes was larger than the magnitude of the decrease in angle crashes. That difference from other studies may have been the result of the investigators’ decision to study the crash narrative and diagram instead of relying only on collision type. Because the number of induced rear-end crashes was so much larger than the number of eliminated red light running (angle) crashes, a net safety gain would be realized if and only if severity of the latter were substantially greater than severity of the former.
Evaluation of Proneness to Red Light Violation
Authors: Giuffrè Tullio , Rinelli Savino
Published: May 2018

Evaluation of proneness to red light running behavior, because it results from human and road factors, can aid in a proper selection of the sites to be treated and thereby increase the benefit of countermeasures to reduce the red light running (RLR) phenomenon. Starting from the conceptual framework of a model based on potential conflicts analysis, this paper shows that a quantitative evaluation of proneness to red light running behavior can be obtained from both the analysis of the effective operational characteristics of the intersection and the actual number of RLR violations. According to behavioral models referred to in the literature, which emphasize the influence that both human and road factors have on the user's decision-making process at red lights, the proposed approach also accounts for the impact of the local (site) and general (population) characteristics on the phenomenon. Field observations for a case study in an urban area are discussed to illustrate the methodological approach. Results obtained clearly show the sensitivity of the parameter assumed for describing proneness to red light violation to the operational characteristics of the intersections. Moreover, they underline that the common violation rates could cause improper evaluation of the extent of the RLR phenomenon at a specific intersection.
Simulated Driving and Attention of Repeat Users of MDMA and THC Compared with THC Users and Non-Drug-Using Controls
Authors: Lamers Caroline T. J. , Rizzo Matthew , Bechara Antoine , Ramaekers Jan
Published: May 2018

The aim of the study is to assess if cognitive impairments in abstinent users of methylenedioxymethamphetamine (MDMA) are due to repeated use of MDMA or concurrent drugs of abuse and how these impairments interfere with key activities of daily life such as automobile driving. Simulated driving performance and attention of 12 users of MDMA and marijuana [tetrahydrocannabinol (THC)] (MDMA/THC), 15 THC users, and 15 non-drug-using, age-matched controls were compared. THC users’ mean speed reduction in response to passing a car parked on the shoulder of the road was 7 mph (11.3 km/h) less than that of controls. Compared with non-drug-using controls, the MDMA/THC users were less able to mitigate the effects of an illegal intersection incursion by another vehicle and entered the collision at a higher speed (42 versus 26 mph). In real life, this 16-mph (26-km/h) difference would increase the likelihood of injuring parties in both colliding vehicles. Processing speed and attention did not differ between groups; this suggests that the lower speed reduction in the MDMA/THC users was more likely due to executive function impairments (incorrect situation interpretation and awareness) than to reduced processing speed. In conclusion, compared with non–drug users, MDMA/THC users may be at a greater risk for driver performance errors that lead to crashes. Because collision speed did not differ between MDMA/THC users and THC users, a specific role of MDMA as opposed to THC toxicity in driving performance impairment remains to be established.
Traffic Safety Attitudes and Driving Behavior of University Students
Authors: Al-Rukaibi Fahad , Ali Mohammed A. , Aljassar Ahmad H.
Published: May 2018

Road safety has become one of the most important traffic issues in Kuwait, along with traffic congestion. On average, one person dies daily in Kuwait because of road accidents; this is in addition to scores of major and minor injuries. A deeply worrying aspect of road accidents in Kuwait is that a vast majority of the dead and seriously injured are young Kuwaiti drivers. The Kuwait government has implemented new and stiffer traffic rules and regulations since November 2001, and the Ministry of the Interior has installed several speed cameras at midblock and intersection locations. Analysis of accident patterns and driving habits in Kuwait reveals that enforcement and engineering alone may not be able to help alleviate the high rate of traffic accidents in Kuwait today. Driver education is probably as important as engineering and enforcement measures. This paper presents the results of a study undertaken to investigate the driving behavior and traffic safety attitudes of young university student drivers. It also examines road traffic accident statistics in Kuwait. Findings of the study indicate that although most students affirm their awareness of traffic rules and claim to be following them usually, a significant number appeared to be oblivious to the disastrous consequences of higher travel speeds. Driver education measures should be effectively used to improve the extremely dangerous traffic safety situation in Kuwait. Education and training before issuing the license and graduated driver licensing policies should also be investigated for implementation in Kuwait.
Sustainable Safety in the Netherlands
Authors: Wegman Fred , Dijkstra Atze , Schermers Govert , Van Vliet Pieter
Published: May 2018

This paper deals with prevention of human errors by proper road planning, road design, and improvement of existing roads within the framework of the Dutch Sustainable Safety vision. This vision focuses on three design principles for road networks and for roads and streets: functionality, homogeneity, and predictability. The ambition is to reduce considerably the number of crashes and casualties and maintain the Netherlands as one of the countries with the best road safety records. This vision was launched at the beginning of the 1990s and accepted as a formal part of Dutch policies in the mid-1990s. It resulted in a so-called Start-Up Program on Sustainable Safety, not only addressing the planning and design of road infrastructure but strongly emphasizing those aspects. Contents of the start-up program are described as the process leading to implementation. An overview presents different (road infrastructure) components of the start-up program and the estimated effects on road crashes. These components are functional road classification, 30-km/h zones and 60-km/h zones, safety of two-wheelers, and roundabouts. Evaluation studies suggest a 6% reduction in the number of fatalities and hospitalizations. Lessons learned will be used in defining the next phase. The start-up program has been used to draft new guidelines and recommendations for road planning and road design. An introduction of that is given. Finally, some thoughts are given about the next phase: how to proceed under circumstances in which fewer public funds will become available.
Major Transportation Accidents in Norway
Authors: Elvik Rune
Published: May 2018

This paper discusses how the long-term frequency of major transportation accidents can be estimated for a small country such as Norway, for which the observed frequency may not be a good estimate for long-term frequency. A major transportation accident is defined as an accident in which there are at least five fatalities. Estimates of the long-term expected frequency of major transportation accidents in Norway are developed by combining information from three sources. They consist of historical records: for Norway for the period 1970 to 2001 (32 years), for Great Britain for 1967 to 2001 (35 years), and for Europe for 1991 to 2003 (12.5 years). The use of formal techniques for decision analysis to help in setting policy priorities in prevention of major transportation accidents is discussed. Also, trade-offs between three safety-related policy objectives are discussed: preventing major accidents, reducing differences in accident risk, and seeking a maximum reduction of the total number of accidents. A trade-off between these policy objectives cannot be made by reliance on a single monetary valuation of safety, but it can in principle be made by treatment of the objectives as attributes of a multi-attributive goal structure that can be maximized by application of multi-attribute utility analysis. Utility values obtained in such an analysis in turn imply a set of monetary valuations reflecting the relative importance of the different policy objectives.
Impact of Wind Forces on Heavy Truck Stability
Authors: Balsom Michael , Wilson Frank R. , Hildebrand Eric
Published: May 2018

A transport truck equipped with instrumentation that measured speed, lateral acceleration, and roll angle of the vehicle was driven around a highway ramp in New Brunswick, Canada, under varying wind conditions. The rollover threshold of the truck was calculated on the basis of characteristics of the vehicle and then compared with the lateral accelerations measured on the truck. Analysis of the data indicated that there was a significant difference in lateral accelerations between different wind speeds, verifying that wind can contribute to rollover. Analysis of the rollover threshold revealed that the lateral accelerations experienced by the truck were often greater than the rollover threshold for brief periods of time, but they were not sufficiently long enough to cause rollover.
Long-Term Effectiveness of Antistripping Additives
Authors: Lu Qing , Harvey John T.
Published: May 2018

Hydrated lime and liquid antistripping agents are often used as additives in asphalt mixes to improve their resistance to moisture damage. Most laboratory studies have evaluated the effectiveness of these additives on the basis of a short-period intensive moisture conditioning procedure, usually a freeze–thaw cycle. Whether this short-term conditioning sufficiently simulates the actual field conditions is unknown. Questions have arisen about the performance of asphalt mixes exposed to moisture for a long period and the effectiveness of antistripping additives after long-term conditioning. This research was conducted in the laboratory to answer these questions to some extent by two test methods: the indirect tensile strength ratio test and the flexural beam fatigue test. A moisture-sensitive mix was treated with the hydrated lime and liquid antistripping agents, saturated by vacuum, and conditioned in a humid environment for a period of up to 1 year. Mix properties were measured and analyzed every 4 months. It was found that most of the detrimental effects of moisture occurred in the first 4 months, and the reduction of strength or stiffness in the late stages became small. Both tests revealed that the antistripping additives were effective even after 1 year of moisture conditioning. Equivalency between the short-term intensive conditioning and the long-term mild conditioning was also found in this study.
Measurements of Moisture Suction and Diffusion Coefficient in Hot-Mix Asphalt and Their Relationships to Moisture Damage
Authors: Kassem Emad , Masad Eyad , Bulut Rifat , Lytton Robert
Published: May 2018

A procedure for measuring the total suction in hot-mix asphalt (HMA) mixes was developed in this study. Suction measurements were related to physical and chemical properties of HMA that influence moisture damage. This procedure was achieved in two phases. In the first phase, the total suction was measured in HMA specimens with different types of aggregates and with different air void distributions and aggregate gradations. The results showed that the drying test using a 60°C temperature-controlled room was the most appropriate setup for measuring the total suction in HMA with thermocouple psychrometers. The characteristics of suction–moisture content curves were found to be related to the air void distribution in HMA and to the resistance of the mixtures to moisture damage. In the second phase, total suction was measured in sand asphalt specimens. These specimens had different combinations of aggregates and binders that exhibited different field resistances to moisture damage. The suction measurements were used to calculate the moisture diffusion coefficient. The results revealed that mixes with a higher diffusion coefficient are those that had poor resistance to moisture damage.
Evaluation of Effect of Heat-Adhesive Emulsions for Tack Coats with Shear Test
Authors: Recasens Rodrigo Miró , Martínez Adriana , Jiménez Félix Pérez
Published: May 2018

The use of conventional emulsions for tack coats can cause problems since they frequently stick to the tires of construction vehicles. Consequently the bond between the asphalt layers is inadequate. The importance of tack coats in pavement performance means that bituminous emulsions are constantly being improved. Recently new types of emulsions have been developed from low penetration bitumen that contains no flux. These emulsions are known as heat-adhesive emulsions, and they are resistant to construction vehicles. The purpose of this study is to analyze the effect of different heat-adhesive emulsions and to verify their performance in service in comparison with the response of a conventional emulsion. For this reason a new shear test was developed in the Road Research Laboratory [Laboratorio de Caminos de Barcelona (LCB)] of the Technical University of Catalonia, in Barcelona, Spain. The LCB test is carried out at different temperatures, both on laboratory specimens and on cores extracted from recently constructed pavements, in which the same emulsions and dosages have been used. The application of the LCB test shows that the performance of the different heat-adhesive emulsions mainly depends on the characteristics of the base bitumen and the kind of modifier used. At low temperatures, heat-adhesive emulsions reach, in general terms, lower shear resistances than those of conventional emulsions; however, at intermediate temperatures there are heat-adhesive emulsions with both higher and lower strengths than those of the conventional emulsions.
Micromechanical Modeling Approach to Predict Compressive Dynamic Moduli of Asphalt Mixtures Using the Distinct Element Method
Authors: You Zhanping , Buttlar William G.
Published: May 2018

A clustered distinct element method (DEM) approach is presented as a research tool for modeling asphalt concrete microstructure. The approach involves the processing of high-resolution optical images to create a synthetic, reconstructed mechanical model that appears to capture many important features of the complex morphology of asphalt concrete. Uniaxial compression tests in the laboratory were employed to measure the dynamic modulus of sand mastic (a very fine sand–asphalt mixture) and asphalt mixtures at three temperatures and four loading frequencies. For a coarse mixture considered in this study, it was found that a two-dimensional (2-D) clustered DEM provided good estimates of mixture dynamic modulus across a range of loading temperatures and frequencies without calibration. However, for a fine-grained mixture, the uncalibrated predictions of the 2-D model were found to reside near the lower theoretical bounds and well below experimentally determined moduli, most likely because of current limitations in scanning and modeling resolution and the nature of the 2-D microstructural description. Work is under way to extend the model to three dimensions and to consider linear viscoelastic behavior in the mastic. That notwithstanding, the current modeling approach was successfully implemented in recent follow-up studies to portray bulk material behavior in conjunction with fracture models to study crack behavior in hot-mix asphalt.
Evaluation of Healing Property of Asphalt Mixtures
Authors: Kim Booil , Roque Reynaldo
Published: May 2018

Although repeated traffic loading causes damage to accumulate in asphalt pavements, the damage heals during rest periods (time between traffic loadings). Consequently, this healing enhances the fatigue life of the pavement. A method was developed to determine the healing rate of asphalt mixtures in terms of recovered dissipated creep strain energy (DCSE) per unit time. The healing properties of four different asphalt mixtures were evaluated with this approach. The test procedure consists of a repeated loading test and periodic resilient modulus tests. A normalized healing rate in terms of DCSE/DCSEapplied was defined to evaluate the healing properties independent of the amount of damage incurred in the mixture. From the test results, it was determined that the healing rates of the asphalt mixtures tested increased dramatically above 10°C and were more affected by the aggregate structural characteristics (i.e., aggregate interlock, film thickness, voids in mineral aggregate) of the mixtures than by polymer modification. Although styrene-butadiene-styrene polymer modification reduced the rate of damage accumulation, it had no effect on the healing rate of the mixtures tested.
Mechanical Mixture Simulation Devices for Determining and Calibrating Internal Angle of Gyration in Superpave Gyratory Compactor
Authors: Anderson R. Michael , Hall Kevin D. , Huner Michael
Published: May 2018

Since 1993, asphalt technologists have recognized the importance of maintaining a tight tolerance on the angle of gyration used in the Superpave® gyratory compactor. Small changes in angle were shown to affect significantly the percentage of air voids in a compacted mix specimen and, in the design phase, to affect the design asphalt binder content. Through the years since its implementation, there have been significant advancements in the understanding of the Superpave gyratory compactor. Implementation research indicated that the internal angle of gyration was the compaction parameter of importance and that it did not directly relate to the measured external angle of gyration. Continuing to seek improvements in reproducibility of test results, the industry developed several devices that mechanically simulate the stiffness of an asphalt mixture so that determination and calibration of the internal angle of gyration can be accomplished without the necessity of compacting mixture specimens. The purpose of this research was to improve the determination and subsequent calibration of the dynamic internal angle of gyration for the Superpave gyratory compactor by evaluating the use of the mechanical mixture simulation devices. The results of the research indicate that mechanical mixture simulation devices can be used to effectively determine and calibrate the internal angle of gyration. By streamlining and standardizing the process for determining and calibrating the internal angle, it is expected that the variation in the bulk specific gravity (or percentage of air voids) of a compacted mixture specimen between user agencies and producers will be significantly reduced.