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Past design consistency research has demonstrated the relationship between operating speeds and geometric design features on two-lane rural highways. However, little is known about the relationship between geometric design consistency and traffic safety. In this study, design consistency is referred to as the difference between operating speed and inferred design speed, and design consistency density is measured to account for the effect of elements upstream and downstream of the study element. To perform the design consistency--safety evaluation in the present study, geometric design, roadway inventory, crash, and operating speed data were collected along two case-study highways in central Pennsylvania (U.S. 322 and PA 350). Several count regression model formulations were used to explore the statistical association between design consistency and total crash frequency. A statistically significant positive association between geometric design consistency and safety was found. Design consistency surrounding the study elements was also found to increase the expected crash frequency in the study element. The significant effects of design consistency and design consistency density measures on crash frequency for the two case-study sites indicate that there is value in further considering the relationship between design consistency and safety in future research, particularly in the context of the highway safety manual crash-prediction algorithm. DOI: 10.1061/(ASCE)TE.1943-5436.0000553. CE Database subject headings: Traffic speed; Geometry; Highways and Roads; Traffic Safety; Statistics. Author keywords: Design consistency; Two-lane highways; Geometric design; Inferred design speed; Crash frequency.

Providing adequate nighttime visibility to roadway users is an important consideration for state and local transportation agencies. Driving at night is less dangerous when pavement markings are easily discernable. Retroreflectivity is a measure of nighttime visibility. Transportation agencies could use estimates of the expected service life of pavement markings to plan restriping operations at a time when markings are near a minimum threshold level of retroreflectivity. The present study proposes the use of an artificial neural network to predict pavement marking retroreftectivity as a function of initial retroreflectivity, the age of the markings, traffic flow, pavement marking type, and route location information using data from North Carolina. The results show that many of the input variables have a nonlinear association with pavement marking retroreflectivity. Surface plots of the degradation pattern are provided to illustrate the relationship between input and output variables. Estimates of service life are provided to show how the output can be used to manage pavement marking systems. DOI: 10.1061/(ASCE)TE.1943-5436.0000194 CE Database subject headings: Pavement markings; Neural networks; North Carolina; Degradation; Service life. Author keywords: Pavement markings; Neural networks; North Carolina; Degradation; Service life.

Past speed-related research has focused on the operational effects of roadway geometrics along rural two-lane highways using ordinary least-squares regression models. More recent research has focused on the association of traffic flow characteristics on vehicle operating speeds along multilane, limited access highways using a simultaneous equations approach. Few research studies, however, have been conducted to determine the combined association between various geometric design features and traffic flow on operating speeds along multilane highways. This research considers both geometric design and traffic flow parameters, in a simultaneous equations framework, to model the mean operating speed and speed deviation on four-lane highways (two lanes in each direction). Models for both left- and right-lane mean speeds and speed deviations were estimated. The three-stage least-squares estimator was used to investigate the possible endogeneity of mean speed and speed deviation in the system of equations and to account for the contemporaneous correlation between the disturbances across the equations. The results indicate that different geometric design features are associated with mean speed and speed deviation in the left- and right-lane models. As such, it is recommended that future multilane highway speed models consider using a simultaneous equations framework. DOI: 10.1061/(ASCE)TE.1943-5436.0000149 CE Database subject headings: Regression models; Highways and roads; Traffic speed; Predictions; Equations of motion. Author keywords: Simultaneous equations; Regression models; Operating speed; Multilane highways.

Two-lane rural highways attract trips between traffic generators such as residential villages or small commercial areas and are generally uninterrupted flow facilities that provide a high level of mobility with high posted speeds limits. When passing through developed areas, the posted speed limit may be lowered to encourage reduced vehicle operating speeds. No published guidelines currently exist for the design of transition zones that connect high-to low-speed operating environments on two-lane rural highways. The objective of this research was to collect operating speed and roadway characteristic data along two-lane rural highway transition zones in Pennsylvania to explore the roadway, roadside, and traffic control factors that are associated with driver speed differentials. Single- and multilevel models were estimated and compared. The posted speed limit reduction as well as a change in the paved shoulder width, total number of driveways, various advance warning signs, the transition zone length, and the presence of horizontal curves were shown to increase the expected speed reduction in transition zones in the models. Additionally, drivers entering transition zones at higher speeds were found to have greater speed reductions than drivers entering the transition zone at lower speeds. DOI: 10.1061/(ASCE)TE.1943-5436.0000137 CE Database subject headings: Traffic speed; Highways and roads; Design; Driver behavior; Statistics; Rural areas. Author keywords: Traffic speed; Highway and road design; Driver behavior; Statistics.

The interactive highway safety design model (IHSDM) is a suite of software analysis tools used to evaluate safety and operational effects of geometric design on two-lane rural highways. IHSDM checks existing or proposed two-lane highway designs against relevant design policy values and provides estimates of a design's expected safety and operational performance. This paper describes efforts to apply IHSDM to two existing rural roadways (one an arterial and the other a collector) in Pennsylvania and to compare the crash prediction and speed profile results to observed speed and crash data for these same two roadway segments. When considering both case study roadways together, the use of site-specific crash history data, adjusted using the empirical Bayes procedure, and a county-level calibration factor, produced crash frequency predictions that most closely matched the observed crash frequencies. The design consistency module output on the arterial roadway closely matched the observed speeds. On the collector roadway, the predicted and observed speeds did not match closely, thus, underscoring the need to expand the design consistency module capabilities to consider low-speed, complex alignments. DOI: 10.1061/(ASCE)0733-947X(2009)135:2(62) CE Database subject headings: Safety; Highway and road design; Traffic speed; Predictions; Traffic accidents; Pennsylvania; Case reports.