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68 CHAPTER 6 FINDINGS This chapter presents the findings of the research. The issues across all median opening types, with the exceptions of Type addressed in this chapter are accident and field data, median 1a (i.e., conventional midblock median opening without left- opening accident frequencies, median opening accident turn lanes) and Type 3a (i.e., conventional median opening rates, median opening traffic conflicts, comparison of acci- without left-turn lanes at three-leg intersection), which each dent rates and conflict rates, and combinations of median have about one-half the average ADT on the major road. opening types. The median opening volumes represent all U-turns and left turns that go through the median opening, including left turns from the minor road; these volumes are based on ACCIDENT AND FIELD DATA counts made during the field studies. The midblock median Table 29 presents the number of unsignalized median open- openings (Types 1a, 2b, and 2c) have no left-turn volumes ing sites in each of the following categories: given that, by design, they accommodate only U-turn traffic. The median opening volumes constitute a small percentage Median openings in the original catalog, of the major road volumes, ranging from 0.0 to 4.2 percent. Median openings with accident data available, Median openings where field data (either videotape stud- MEDIAN OPENING ACCIDENT FREQUENCIES ies or supplementary traffic counts) were collected, and Median openings with both accident and field data. Tables 31 through 33 present frequencies of total acci- dents, fatal and injury accidents, and PDO accidents, respec- The median openings in the original catalog are all of the tively, by median opening type. U-turn and left-turn accident unsignalized median openings that were visited and docu- frequencies are presented separately as well as in combina- mented in the field. They represent all of the original median tion. These frequencies should not be considered conclusions openings available for possible inclusion in the analyses. about the relative safety of various designs because they do However, accident data were not available for all of the median not consider traffic volumes (i.e., median types showing more openings. In one state, accident data were available only for accidents may also have had higher traffic volumes). intersection locations (i.e., locations with a cross street). Thus, Table 31 demonstrates that accidents related to U-turn and no accident data were available for midblock locations (Types left-turn maneuvers at unsignalized median openings occur 1a, 1b, 2b, and 2c). In other states, some of the corridors orig- very infrequently. The 103 median openings in urban arter- inally recommended by the participating highway agency-- ial corridors experienced an average of 0.41 U-turn plus left- and which were included in the catalog of median opening turn accidents per median opening per year. The 12 median types--were not maintained by the highway agency and, openings in rural arterial corridors experienced an average of therefore, accident data were not available for these locations 0.20 accidents per median opening per year. Overall, at these either. In Table 29, the columns under "Median openings median openings, U-turns represent 58 percent of the median with field data" illustrate the number of median openings opening movements and left turns represent 42 percent of the where videotape studies were conducted ("Primary") and median opening movements. Based on these limited accident where 15-min counts were made ("Supplementary"). The last frequencies, there is no indication that U-turns at unsignal- column represents the median openings with both accident and ized median openings constitute a major safety concern. field data and, given that accident and traffic volume data are Table 34 presents the distribution of collision types by needed to conduct meaningful accident analyses, the median median opening type. Collision types are as follows: openings that were included in the analyses. Thus, the proj- ect database includes 115 unsignalized median opening sites Major-road angle collision--collision between a major- with both accident and field data. road through vehicle and a vehicle turning from the Table 30 summarizes traffic volume data by median open- median opening onto the major road (i.e., either a left- ing type. The average major-road ADT is fairly consistent turning vehicle or a U-turn vehicle)