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27 CHAPTER 3 CURRENT DESIGN POLICIES AND PRACTICES OF HIGHWAY AGENCIES This chapter presents the current design policies and prac- 7 counties responded. Table B-2 in Appendix B lists the state tices of state and local highway agencies related to median and local highway agencies that responded to the survey. The openings at unsignalized intersections. Design policies at the overall response rate was 41 percent, including a response national level are based on the AASHTO Green Book (3). rate of 70 percent for state highway agencies and 28 percent Many states also have their own geometric design manuals, for local highway agencies. which may differ from the Green Book in some particulars, and their own access management manuals, which may also present policies concerning location and design of median LOCATION AND DESIGN OF MEDIAN OPENINGS openings. The presentation of state and local agency design policies The AASHTO Green Book provides guidance on the loca- in this chapter of the report is based on responses to a survey tion and design of median openings in Chapter 6 (Collector questionnaire sent to state and local highway agencies. The Roads and Streets) and Chapter 9 (Intersections) (3). In both questionnaire is presented in Appendix A of this report and chapters, the Green Book recommends that median openings the responses of highway agencies to the questionnaire are on divided highways with depressed or raised curbed medians presented in Appendix B. The questionnaire addresses high- only be provided for street intersections or for major develop- way agency policies concerning location and design of median ments and that spacing between median openings should be openings, treatment of U-turns at median openings, traffic adequate to allow for introduction of left-turn lanes. In Chap- operational and safety problems at median openings, and ter 9, the Green Book recommends that the design of a effectiveness of various mitigation measures. median opening and median ends should be based on traffic volumes, urban-rural area characteristics, and type of turning SURVEY RECIPIENTS vehicles. Highway agencies were asked about the types of median The mailing list for the survey consisted of openings that they use. All agencies stated that they use con- ventional (i.e., nondirectional) median openings on divided · 50 state highway agencies and highway. Most of the agencies use directional median open- · 109 local highway agencies (94 cities and 15 counties). ings either frequently or occasionally. Thus, a total of 159 survey questionnaires were mailed. Location The questionnaires for state highway agencies were gener- ally sent to the state traffic engineer. The names and addresses Highway agencies were asked about the criteria they use of the state traffic engineers were determined from the mem- to determine the location of median openings. The types of bership roster of the AASHTO directory. policies used by the responding agencies include AASHTO Most of the local highway agency engineers on the mail- policy, state or local design policy, state or local access man- ing list for the questionnaires were obtained from the ITE agement policy, general guidelines (i.e., lists of factors con- directory. The local agencies included approximately two sidered as an informal policy), and engineering judgment. major cities from each state and 15 selected urban or subur- When asked about the factors considered in determining the ban counties. Rural counties were not surveyed because they location of median openings, the three most commonly cited are unlikely to operate many divided highways. factors were proximity to other median openings, traffic vol- umes, and locations and functional classes of public road inter- RESPONSE RATE sections. Other frequently mentioned factors included sight distance, operational efficiency, safety, area type, speed, avail- Table 10 summarizes the 65 responses to the 159 median ability of sufficient length to accommodate left-turn lanes, and opening surveys sent. Thirty-five state agencies, 23 cities, and median width.