This paper studies different specifications of fundamental diagrams for first-order dynamic traffic modeling. The fundamental diagram, which refers to the relationship between traffic flow and density at a given location, plays an important role in modeling the dynamics of traffic propagation. Many forms of fundamental diagrams have been proposed since the seminal work of Greenshields 80 years ago. Nevertheless, empirical validation of fundamental diagrams, in particular, for dynamic modeling purposes, is limited. The study is conducted with an extensive dataset collected from the U.K. M25 motorway. This paper highlights the difficulty in modeling congested traffic with single-valued fundamental diagrams and fine-grained loop detector data. Consequently, this paper first analyzes and discusses the effect of data granularity on model calibration and application. Following this, a set-valued fundamental diagram modeling approach with fine-grained data is also presented. This paper contributes to the development and validation of dynamic traffic simulation tools.

Nearly 40–50% of crashes involving drowsy driving result in occupants’ fatalities or injuries in the United States. Furthermore, such crashes have been underreported, due to deficiencies in the law enforcement’s crash reporting forms and the difficulty of attributing crashes to drowsy driving with lack of drivers’ information. Thus, it is important for people to be aware of the risk of drowsy driving, and methods and efforts to reduce such crashes should be taken into account. This paper discussed some research findings during the course of developing a drowsy driving advisory (DDA) system, an engineering countermeasure to reduce such crashes. Characteristics of drowsy driving crashes and relationships between the crashes and the location of rest areas were investigated through a crash analysis. The crash analysis showed that (1) drowsy driving crash rates are higher at rural interstate sections than those at urban sections, and (2) the location of drowsy driving crashes is correlated to the location of roadside rest areas. A list of safety messages were developed for the DDA system and were introduced at a public survey where people’s preferences to the messages were observed. The survey results showed that the safety messages with practical and specific examples of drowsy driving risk received a noticeably higher response ratio from survey participants as compared to the ones with general and nonspecific examples. In addition, a large fraction of survey participants said they would consider stopping and resting if they see the safety messages on the road.

In order to evaluate the effectiveness of different pothole patching methods and materials, it is necessary to conduct a long-term field survey of patches installed at different environmental and traffic conditions. The research reported in this paper investigated the service life of different throw-and-roll pothole patches through a 14-month field survey. Three statistical methods, including (1) logistic regression, (2) classification tree, and (3) survival analysis, were employed to characterize the influence of different factors on the service life of installed patches, and to identify the performance of different patching materials. The factors investigated in the research reported in this paper included the length, width, and depth of patches; traffic level; speed limit; and freeze times. All the three statistical methods identified similar trends of the significance of factors and performance rankings of materials. Generally, patches installed on road sections with less freeze cycles, lower speed limit, and lower traffic level had significantly longer service life. A cold bag mix had significantly longer service life. In addition, the classification tree method indicated that significant influences of weather conditions and materials on the service life of patches were only observed around 1 year after the installation, indicating the necessity of the long-term survey.

The main objective of this paper is to identify the most appropriate rehabilitation method for composite pavements and to evaluate the influence of different factors for the reflective crack development in composite pavement by survival analysis. Four composite pavement rehabilitation methods are evaluated: mill and fill, overlay, heater scarification, and rubblization. Survival analysis is used to evaluate the four methods using three pavement performance indicators: reflective cracking, international roughness index (IRI), and pavement condition index (PCI). Rubblization can significantly retard reflective cracking development compared with the other three methods. No significant difference for PCI is seen in the survival analysis for the four rehabilitation methods. Heater scarification shows the lowest survival probability for both reflective cracking and IRI, whereas overlay results in the poorest overall pavement condition based on PCI. Parametric survival models are employed to further analyze the factors influencing reflective cracking for the four composite pavement rehabilitation methods. Traffic level is found to not be a significant factor for reflective cracking development. An increase in overlay thickness can significantly delay the propagation of reflective cracking for all treatment methods (not including rubblization). Soil types in rubblization pavement sites are assessed, and no close relationship is found between rubblized pavement performance and subgrade soil condition.

It is well-known that the performance of Portland cement concrete (PCC) pavement depends, to a great extent, on the support condition under the slab. The Texas Department of Transportation (TXDOT) recognized the importance of the support condition and requires the use of a stabilized base, either a 10.16-cm hot mix asphalt layer or a minimum 2.54-cm asphalt concrete over a 15.24-cm cement-stabilized layer. For pavement design purposes, $81.4\mathrm{MPa}/\mathrm{m}$ has been used as the default value for the modulus of the subgrade reaction ($k$ value) for the support provided by these bases. The use of a single value of $81.4\mathrm{MPa}/\mathrm{m}$ for the $k$ value in rigid pavement design was partly because of the insensitivity of the required slab thickness to the modulus of the subgrade reaction in the current TXDOT rigid pavement design procedure. To improve rigid pavement design, TXDOT developed a new design procedure for continuously reinforced concrete pavement (CRCP) on the basis of mechanistic-empirical principles and plans to implement the procedure. In this design procedure, the slab support has rather more substantial effects on the required slab thickness than the current TXDOT design procedure. To increase the reliability of the new pavement design procedure, accurate evaluations of the $k$ value are important. A test section was constructed in which various base types were used, and a number of field tests were conducted to estimate the range of $k$ values for the support systems that are currently used or expected to be utilized, including the placement of nonwoven geotextile in lieu of the asphalt layer. The current practice of using one default value of $81.4\mathrm{MPa}/\mathrm{m}$ needs to be revised, and the use of nonwoven geotextile is not recommended until further evaluations prove its viability.