David B. Clarke

Evaluation of Interstate Highway Capacity for Short-Term Work Zone Lane Closures

The need to maintain adequate traffic flow through short-term Interstate work zones is paramount on todays heavily traveled freeways. Numerous states have policies related to traffic flow thresholds, vehicle delay, and vehicle queue lengths that provide guidance on conditions when shortterm lane closures can be instituted. Generally, traffic flow threshold limits are a function of traffic-stream characteristics, highway geometry, work zone location, type of construction activities, and work zone configuration. A research study was initiated in South Carolina to examine quantitatively the development and implementation of a methodology for use in determining an updated lane-closure policy based on statespecific parameters. The study focused on determining the number of vehicles per lane per hour that can pass through short-term Interstate work zone lane closures with minimal or acceptable levels of delay. Research tasks included a survey of policies of other states, field-data collection, and methodology development. A methodology was developed with field data collected from 22 work zone sites along South Carolinas Interstate system. Data were obtained during a 12-month period from September 2001 to August 2002. Data collection procedures and data analysis methods employed in model development are summarized. Results of this study may be helpful to state highway agencies interested in developing similar research-based policy guidelines for short-term Interstate lane closures in their jurisdictions.

Analyzing the effectiveness of implemented highway safety laws for traffic safety across U.S. states

ABSTRACT Since highway safety laws vary greatly from state to state in the U.S., there is a need to analyze the effectiveness and performances of the implemented highway safety laws. The random-parameter zero-truncated negative binomial (RZTNB) models are proposed to analyze the effects of highway safety laws on fatal crashes at state levels. The results show that the proposed models are useful in describing the relationships between the fatal crashes and the explanatory variables with better goodness of fit. By accounting for the heterogeneities, the RZTNB model outperforms the negative binomial model and reveals new insights. The findings indicate that (1) compared to the secondary ban, the primary handheld cellphone ban is more effective; (2) establishing reasonable and acceptable speed limits can enhance the traffic safety; and (3) the implemented speed camera system and ignition interlock device have weaknesses and alternative methods should be considered when upgrading laws and regulations.

Analyzing injury crashes using random-parameter bivariate regression models

ABSTRACT This paper proposes a random-parameter bivariate zero-inflated negative binomial (RBZINB) regression model for analyzing the effects of investigated variables on crash frequencies. A Bayesian approach is employed as the estimation method, which has the strength of accounting for the uncertainties related to models and parameter values. The modeling framework has been applied to the bivariate injury crash counts obtained from 1000 intersections in Tennessee over a five-year period. The results reveal that the proposed RBZINB model outperforms other investigated models and provides a superior fit. The proposed RBZINB model is useful in gaining new insights into how crash occurrences are influenced by the risk factors. In addition, the empirical studies show that the proposed RBZINB model has a smaller prediction bias and variance, as well as more accurate coverage probability in estimating model parameters and crash-free probabilities.

LANDSIDE ACCESS TO SEAPORTS IN URBAN AREAS: A CASE STUDY

Seaports in the United States usually are located in urban areas. They are major traffic generators on the landside. However, the landside access needs of ports often are overlooked by the transportation and land-use planning processes. A case study of three ports on the East Coast of the United States was performed: Savannah, Georgia; Wilmington, North Carolina; and Morehead City, North Carolina. Both highway and rail access issues were examined at regional and local levels. Several serious issues and problems are identified and discussed in the paper, including effects on local communities.

Calibration and Validation of Quick Response Forecasting Parameters for Cities in Rural Counties of South Carolina

Quick response travel forecasting techniques have been applied extensively since they became prevalent in the late 1970s. These techniques involve using transferable parameters developed from survey and other empirical data to assist transportation planners to model small urban areas with populations greater than 50,000. The usefulness of the quick response techniques and parameters that are currently in wide application are questionable for cities in rural counties because they were not originally designed for use in areas with populations of fewer than 50,000 people. The research described addresses a critical need for planning tools oriented to smaller cities. This project focused on developing transferable travel demand forecasting parameters that targeted areas of the state of South Carolina with diverse populations and per capita incomes lower than the national average. The findings of this project should allow planners throughout rural areas of South Carolina and similar states to make more reliable estimates of future traffic identified in long-range plans. The calibrated parameters also should be useful for cities in other states that have fewer than 50,000 people and that have demographic and socioeconomic characteristics similar to those of the cities that were modeled as part of this research.

A comparative study of rail-pedestrian trespassing crash injury severity between highway-rail grade crossings and non-crossings

Rail-trespassing crashes that involve various levels of injuries to pedestrians are under-researched. Rail trespassing could occur at crossings where pedestrians are present at the wrong time and at non-crossings where pedestrians are not legally allowed to be present. This paper presents a comparative study examining rail-trespassing crashes in two contexts: highway-rail grade crossings vs. non-crossings. How pre-crash trespassing behaviors and other factors (e.g., crash time, locations, and socio-demographics) differ between grade crossings and non-crossings are explored. The analysis relies on a ten-year (2006-2015) database of rail-pedestrian trespassing crash records extracted from a Federal Railroad Administration safety database. Of these 7157 rail-pedestrian trespassing crashes, 6236 (87%) occurred at non-crossings, while 921 (13%) occurred at grade crossings. About 60% of the crashes were fatal at both crossings and non-crossings. The most prevalent pre-crash trespassing behavior is running or walking, 63% at grade crossings and 44% at non-crossings. Lying or sleeping account for 29% of non-crossing crashes, whereas they are 3.6% at grade crossings. A unique aspect of the study is that a diverse set of variables based on geographic variations across counties along with crash or injury data are modeled. Considering the data structure and heterogeneity that may exist due to unobserved factors, the multilevel mixed-effect ordered logistic regressions models are estimated. The results show that the correlates of injury severity differ across highway-rail grade crossings and non-crossings. For example, lying or sleeping on or near tracks contributed to higher chances of fatal injury in both contexts, however, they were relatively more injurious at grade crossings. The analytical results can provide guidance on railway safety improvement plans.

Exploring the effects of state highway safety laws and sociocultural characteristics on fatal crashes.

ABSTRACT Objective: Distinguished from the traditional perspectives in crash analyses, which examined the effects of geometric design features, traffic factors, and other relevant attributes on the crash frequencies of roadway entities, our study focuses on exploring the effects of highway safety laws, as well as sociocultural characteristics, on fatal crashes across states. Methods: Law and regulation related data were collected from the Insurance Institute for Highway Safety, State Highway Safety Offices, and Governors Highway Safety Association. A variety of sociodemographic characteristics were obtained from the U.S. Census Bureau. In addition, cultural factors and other attributes from a variety of resources are considered and incorporated in the modeling process. These data and fatal crash counts were collected for the 50 U.S. states and the District of Columbia and were analyzed using zero-truncated negative binomial (ZTNB) regression models. Results: The results show that, in law and regulation–related factors, the use of speed cameras, no handheld cell phone ban, limited handheld cell phone ban, and no text messaging ban are found to have significant effects on fatal crashes. Regarding sociocultural characteristics, married couples with both husband and wife in the labor force are found to be associated with lower crash frequencies, the ratios of workers traveling to work by carpool, those driving alone, workers working outside the county of residence, language other than English and limited English fluency, and the number of licensed drivers are found to be associated with higher crash frequencies. Conclusions: Through reviewing and modeling existing state highway safety laws and sociocultural characteristics, the results reveal new insights that could influence policy making. In addition, the results would benefit amending existing laws and regulations and provide testimony about highway safety issues before lawmakers consider new legislation.

Effect of the combined centre of gravity on the running safety of freight wagons

ABSTRACT This paper presents an analysis of loaded freight wagon dynamics in curve alignments. We investigate the effects of the combined centre of gravity (CCOG) on the running safety of freight wagons and examine proper position of the CCOG. A simple wagon-rail model is implemented using the multibody dynamics software ADAMS/Rail. The simulation model is operated on curve tracks with various radii and velocities and the curving performances are evaluated. The results indicate that the CCOG can be located within a flexible and accurate range. The longitudinal offset is good for the curving performance and the permissible lateral offset should be assessed based on the curve radius and cant deficiency.

Application of Granular Material Pressure Cells to Measure Railroad Track Tie/Ballast Interfacial Pressures

This paper describes the development of a method to measure railroad track tie/ballast interfacial pressures using pressure cells specially designed for granular materials. Repeat measurements were taken during a several-month period on a Norfolk Southern Corporation high-tonnage mainline. The research employed new wood crossties routed so pressure cells could be recessed within the ties. Thus, the active surfaces of the pressure cells were flush with the tie bottoms. Cabling was run through a recess to the tie end. This greatly reduced the likelihood of damage to the instrumentation during track surfacing and lining activity. The ties were installed such that multiple cells were directly under consecutive rail seats of one rail. Several ties also had cells either at the center or the rail seat of the opposite rail. The researchers expended considerable effort to provide consistent ballast conditions for the instrumented ties and adjacent, undisturbed (transition) ties. Norfolk Southern crews surfaced and tamped through and on either side of the test section. This, plus consolidation through normal accruing train traffic, resulted in consistent measurements through the section. The paper presents ballast pressure magnitudes and distributions and discusses results, including the effects of variable ballast support, wheel loadings, and impact loadings. Typical vertical ballast pressure measurements directly under the rail seat, with compacted ballast and minimal impact forces ranged from 20 to 30 psi (140 to 210 kPa) under the heaviest common revenue wheel loadings.

Macrolevel Classification Yard Capacity Modeling

Classification yards play a significant role in railroad freight transportation and are often considered bottlenecks for railroad networks. Based on a generic yard simulation model, the model in the presented study fits the Bureau of Public Roads function, which is widely used in highway capacity to represent the volume–dwell time relationship. The proposed analytical model incorporates major features of rail yards, such as the number and capacity of tracks in each area, the number of engines and humps, the humping speed, and the assemble rate. The model is validated by historical data from 16 classification yards of Class I railroads in the United States. The results show that the proposed model can generate precise capacity data of rail yard, as well as the dwell time of rail cars in yards. The dwell time increases sharply when the volume is greater than the capacity of a rail yard. The identified relationship may help a railroad analyze its network at the macro level and therefore improve the systemwide capacity and efficiency.