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The primary purpose of longitudinal median barriers is to redirect errant vehicles that depart the roadway and thus prevent collisions with opposing traffic, terrain features, or roadside objects, which could lead to severe impacts. In the study reported in this paper, vehicle dynamics analysis was used to identify the influences of varying median configurations on interface effectiveness of barrier lateral placement options. The same approach taken in previous efforts to consider five vehicle types for a range of impact conditions was taken here, except that only uniform median configurations were considered. The variations in median shape, side slopes, and roadway elevations in the analyses were reflected in nonsymmetrical override and underride limits. Data for a road section under consideration for median improvement provided the basis for the assessment of the effects of variations in median configuration. Placement effectiveness plots were generated with vehicle dynamics tools for two barrier designs. The results showed effects on lateral placement locations resulted from atypical median configurations and in situations in which there was variation in the relative elevations of the roadways on a divided highway. The results suggested a need to consider the effects of transitions in the median configuration when the barrier type and the lateral position are selected for the full length of a project. The results enhanced understanding of the effectiveness of median barrier placement with various median configurations and barrier options.

Various types of roadside safety hardware are deployed along highways to safely redirect or contain errant vehicles such that there is no intrusion into a hazardous area or on-coming traffic that may cause harm to the drivers or occupants. Primary factors for the crashworthiness evaluation of these hardwares include structural adequacy, occupant risk, and after-collision vehicle trajectory. Suspension characteristics of the vehicle and tires interaction with safety hardware and surface conditions could influence all these factors. Simulation efforts have resulted in increasingly better replications of crash events, but it has been noted that tire behaviors and failures are still not predicted well. This article will describe efforts to improve the finite element modeling technique of a vehicle tire. A new tire model, having the physical structure of a tire that could influence the nature of operational and crash-induced loading of the tire is presented. Techniques for characterizing the tire material and suspension properties are discussed. Correlation between the simulation results and the full-scale crash testing data is discussed. Measures for assessing occupant injury risk and occupant impact severity are evaluated for both sets of data. Finally, preliminary results using the new tire model in vehicle impact simulations to investigate the effect on vehicle stability, subject to variations in impact conditions such as speed and angle, are presented.

The National Crash Analysis Center (NCAC) at the George Washington University simulated the crash of a 2,270-kg Chevrolet Silverado pickup truck into a standard 32-in. New Jersey shape concrete barrier under the requirements of Test 3–11 of the Manual for Assessing Safety Hardware (MASH). The new, detailed finite element (FE) model for the Chevrolet Silverado was used as the surrogate for the MASH 2270P test vehicle. An FE model of the New Jersey barrier was drawn from the array of NCAC hardware models. The primary objective of this analysis was to simulate the crash test conducted to evaluate how this commonly used, NCHRP 350–approved device would perform under the more rigorous MASH crashworthiness criteria. A secondary objective was to use newly developed verification and validation (V&V) procedures to compare the results of the detailed simulation with the results of crash tests undertaken as part of another project. The crash simulation was successfully executed with the detailed Silverado FE model and NCAC models of the New Jersey concrete barrier. Traditional comparisons of the simulation results and the data derived from the crash test suggested that the modeling provided viable results. Further comparisons employing the V&V procedures provided a structured assessment across multiple factors reflected in the phenomena importance ranking table. Statistical measures of the accuracy of the test in comparison with simulation results provided a more robust validation than previous approaches. These comparisons further confirmed that the model was able to replicate impacts with a 2270P vehicle, as required by MASH.

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 collec...

The primary purpose of longitudinal safety barriers, such as cable barriers, is to contain or redirect errant vehicles that depart the roadway and thereby keep them from entering opposing travel lanes or encountering terrain features and roadside objects that may cause severe impacts. In this study, finite element analysis, vehicle dynamics analysis, and full-scale crash testing were performed to study the effects of sloped terrain on the safety performance of cable median barriers. A detailed finite element model of a three-strand cable barrier was developed and validated against a previously conducted full-scale crash test. The full-scale crash test and simulation were set up for an impact of the cable barrier with a 2,000-kg (4,400-lb) pickup truck at an angle of 25° and an initial velocity of 100 km/h (62 mph). This setup is in accordance with NCHRP Report 350 guidelines for Test Level 3 safety performance. With this model, computer simulations were performed to assess the performance of the barrier under different impact scenarios and with different terrain profiles. Vehicle dynamics analyses were also conducted to compute the trajectory and dynamics of the vehicle as it crossed the sloped terrain and struck the cable median barrier. On completion of the computer simulation analyses, full-scale crash testing was performed to validate the results.

Background and current status of the development of updated minimum in-service retroreflectivity levels for traffic signs in the United States are described. A summary of the earlier work, conducted from the late 1980s to the mid-1990s, is provided along with descriptions of the relevant validation work. Related events that occurred in the late 1990s are described, and it is shown how, when combined with the assumptions and limitations of the earlier minimum retroreflectivity research, they resulted in a need for updated minimum retroreflectivity levels. The research related to the updated minimum retroreflectivity levels is summarized. A brief description of a second round of national minimum retroreflectivity workshops is also provided. The most recent set of recommended minimum retroreflectivity levels for traffic signs is presented along with a list of suggested research topics based on the limitations associated with the recommendations.

The FHWA Turner-Fairbank Highway Research Center is undertaking a research program to study the visibility of retroreflective raised pavement markers (RRPMs). The focus of the initial effort is to determine the relative luminance of RRPMs and pavement markings (PMs) needed to produce adequate guidance on rural two-lane roadways at night. A driving simulator was used to test 36 research participants as they drove simulated roadways containing various combinations of RRPMs and PMs. The luminance of the simulated roadway delineation ranged from 0.07 to 4.1 cd/m2. The primary driver performance measure was curve-recognition distance. For the various RRPM and PM luminance conditions, mean curve-recognition distances ranged from 19.0 m (62.3 ft) to 68.4 m (224 ft), with a grand mean of 43.0 m (141 ft). Regression analyses produced predictive equations to estimate the mean curve-recognition distance from the luminance of RRPMs acting alone or of PMs acting alone. Trading ratios were computed for PM luminance with and without RRPMs present on the road. A conservative empirical estimate of 0.52 was computed for such a trading ratio based on the data from the current experiment. This value compared favorably with independent estimates of 0.54 and 0.55 based on an earlier analytical approach. Thus, the current experiment confirmed, with empirical data, earlier estimates that it might be possible to reduce the luminance of PMs on rural two-lane roads by about 45% when appropriate RRPMs are installed.

Highway agencies are continually called upon to make decisions about roadside safety projects by considering their relative benefits and costs. ROADSIDE software is a tool developed in the late 1980s for costeffectiveness analysis of safety features and has been used by different highway agencies. As a part of the continuing effort to improve such costeffectiveness procedures, the Roadside Safety Analysis Program (RSAP) has recently been developed at the Texas Transportation Institute. RSAP uses a simulation technique to replicate single-vehicle accidents on a highway facility and can test the effectiveness of the various countermeasures that are used to reduce the severities of these accidents. The application of RSAP to actual case study sites and the outcome of a study recently conducted at Wayne State University are described. Various median treatments on freeways were tested, and their respective benefit-cost ratios, as estimated by RSAP output, were examined. A set of sensitivity analyses of the RSAP output to various input parameters was also conducted. It is found that RSAP is user-friendly software and is fully operational on a personal computer with a Pentium processor in the Windows 95 environment. RSAP provides a summary of the accidents predicted for each scenario tested, and those are segregated by each feature coded along with its respective severity and cost. The economic analysis procedure is based on strong analytic principles, and the results are sensitive to accident cost, cost of construction, and interest rate. The software output is generally sensitive to the input parameters, and the trends appear to be logical. Additional research to calibrate the accident prediction model with historic accident data at the project site will be highly desirable.

The development and application of a computer model for testing the feasibility of multiple agency development projects at proposed transit stations is described. Given a development strategy, the model allocates project costs and revenues among a number of participating entities and uses the `Internal Rate of Return' technique to compute the project returns to each entity. An iterative technique is used to derive the return by converging the numerical value of the `Net Present Worth' of the cash flow to zero by systematically altering the interest rate. The return for each entity is calculated the model in the form of a three dimensional matrix as a function of the type, location and strategy of the project. The model can also estimate annual net return/cost for each entity for a specified interest rate. The study shows that the model can be used to identify optimal development strategies for a given project, economically feasible development projects at a given site, and desirable sites for development projects from a number of possible alternatives.

Joint development (JD) is a process by which major public facilities are constructed in concert with other projects through the coordinated efforts of public or private agencies, or both. This paper focuses upon the identification and analysis of JD mechanisms for use in the Detroit area where major transit investments are anticipated. A total of nine basic types of JD mechanisms were identified and evaluated in the context of the institutional structure of the area. The mechanisms were evaluated for feasibility by considering statutory basis, taxation issues, revenue sources, bonding authority, public approval, jurisdiction, organizational basis, and other relevant aspects. The evaluation indicated that many JD mechanisms could be considered feasible for use in the Detroit area. In some cases, precedents existed for the use of particular tools. In addition, several local agencies were found to have the authority and capabilities to administer JD programs.

The Detroit Metropolitan Area was used as the experimental site for such feasibility testing. Two priority ranking methodologies were developed based upon provisions of rating and ranking methods. Station development potential was identified by a set of socio-economic and land use indicators, and the viewpoints of local professionals were solicited in assessing the relative importance of the indicators identified. Next, the relative rankings for 37 proposed transit stations on two travel corridors were developed using the indicators and the viewpoints of the local professionals. The study shows that it is possible to prioritize station locations for joint development based upon selected socio-economic and land use indicators. The results also suggest that the station ranks obtained by the two methods are not likely to be affected by input solicited from local professionals. Lastly, the procedures developed are found to be sensitive to selection of the indicators.