Passing and no-passing zones are marked on the centerline of two-lane undivided highways, and on three-lane undivided highways where passing is permitted in the opposing direction to a passing lane, to identify areas where the available passing sight distance (PSD) is above or below the minimum values presented in MoDOT’s Engineering Policy Guide (EPG) Table 620.2.2.1, which is identical to Table 3B-1 in the FHWA Manual on Uniform Traffic Control Devices (MUTCD). These minimum PSD values range from 450 ft on 25-mph roads to 1,200 ft on 70 mph roads. The speed level selected for a given road may be based on the 85th-percentile speed of traffic (if available), the posted speed limit, or the speed limit applicable by statute (if no speed limit is posted). PSD is measured from a viewpoint 3.5 ft above the pavement surface (equivalent to the typical height of a driver’s eye) to an object or target height of 3.5 ft. This makes PSD reciprocal–if the driver of one vehicle can see a second vehicle, then the driver of the second vehicle can see the first vehicle. In determining PSD, both vertical and horizontal sight distance must be considered. At crest vertical curves, PSD is limited by roadway geometry alone. At horizontal curves, both roadway geometry and the location of roadside sight obstructions on the inside of the curve must be considered. The PSD criteria used in design used to be substantially larger than those used in marking passing and no-passing zones. However, these were changed in the 2011 AASHTO Green Book, based on research by MRIGlobal in NCHRP Report 605, Passing Sight Distance Criteria (Harwood et al., 2008). Harwood et al. demonstrated that it made little sense to have independent PSD criteria for design of PSD and marking of passing and no-passing zones, so the Green Book and MUTCD criteria are now identical. The MUTCD states that where the distance between successive no-passing zones is less than 400 ft, no-passing markings should connect the two zones; this effectively sets a minimum passing zone length of 400 ft. Harwood et al. (2008) demonstrated that passing zones with lengths between 400 and 800 ft contribute very little traffic operational benefit to two-lane highways. Methods that have been used for locating the boundaries of passing and no-passing zones in the field include: the walking method, the two-vehicle method, the one-vehicle method, the eyeball method, the videolog method, and the laser or optical rangefinder method (Brown and Hummer, 2000). MoDOT has been using the two-vehicle method, but since the equipment for applying this method is now obsolete, MoDOT would like to implement a replacement method based on GPS data that could be collected at highway or near-highway speeds. The objective of the proposed research is to (1) recommend the best method for MoDOT to locate the boundaries of passing and no-passing zones using GPS data and/or other related data collected from a moving vehicle; (2) provide MoDOT with a set of hardware and software to apply the recommended method; and (3) document the recommend method, including the use of the hardware and software, so that the method can be applied by MoDOT. The recommended method will involve automated analysis of data collected from a vehicle moving at highway or near-highway speeds. Methods that involve field staff leaving their vehicle (e.g., the walking method) or that involve slow-moving vehicles were not considered. The hardware will be portable so that it can be easily removed from one vehicle and installed in another. The recommended method will be selected such that the cost to MoDOT to obtain additional sets of the hardware and software needed to apply the method will not exceed $10,000 per unit (i.e., per hardware/software set). The results expected from the research include (1) a recommended and validated method to locate the boundaries of passing and no-passing zones from GPS data concerning the roadway alignment and related information about roadside sight obstructions; (2) a user’s manual explaining how to apply the recommended method to identify the boundaries of passing and nopassing zones, how to utilize the associated hardware and software, and how to manage and store the necessary data for both current use and future application; and (3) delivery to MoDOT of all hardware and software acquired by MRIGlobal during the study and needed by MoDOT to implement the recommended method. Chapter 2 describes the two primary approaches to determining no-passing zone boundaries that were considered early in the research, as well as the benefits and drawbacks of each approach. It then describes the approach that was selected and the considerations that went into that selection from both MoDOT’s and the research team’s perspective. Chapter 3 describes the hardware components used in the system and their functionality. Chapter 4 discusses the development of the field data collection software, including the set-up procedure, the algorithm for measuring and reporting the distance between vehicles, the various messages provided to the driver during data collection, and the process for collecting and recording data in the field. Chapter 5 describes the post-processing software that reports the recommended passing and nopassing zone striping along the length of the roadway in both directions of travel. It provides a description of each data element shown on the output report. Chapter 6 discusses the field testing that was conducted to validate the hardware and software components of the system and presents the degree to which the system’s recommended passing and no-passing zone boundaries align with MoDOT’s existing striping. Chapter 7 presents a discussion of the testing results, describes the current limitations of the system, and suggests areas for further testing and future improvements to the system. Appendix A provides the post-processing system reports for the segments of five routes in Cooper County that were used to test and validate the system. (Author/publisher)
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