Safety of U-Turns at Unsignalized Median Openings (2004)

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

Spacing Approximately one-half of the state and local highway agencies have formal policies concerning the minimum spac- ing between median openings. Most of the states and one of the local agencies that responded have different policies for rural and urban areas. Tables 11 and 12 present median opening spacing policies of state and local highway agencies, respectively, that had numer- ical spacing policies that could be easily summarized. Some agencies had policies based on more variable criteria (e.g., left- turn queue lengths, sight distance, and traffic volumes), which are harder to summarize and are not included in the tables. Table 11 shows that the states that have different spacing policies for rural and urban areas typically require higher median opening spacing in rural areas than in urban areas. The values reported for minimum median opening spacing for rural areas varied from 152 to 805 m (500 to 2,640 ft), while the comparable minimum spacing for urban areas var- ied from 91 to 805 m (300 to 2,640 ft); however, the average minimum median opening spacing was 427 m (1,400 ft) in rural areas and 268 m (880 ft) in urban areas. Table 12 presents the minimum spacing between median openings for the local agencies that presented quantitative minimum median opening spacing values in response to the survey. The general trend of higher minimum median open- ing spacing at rural areas was still present, although the dif- ferences in median opening spacing between area types are not as large as those for state agencies. Left-Turn Treatments Most of the responding agencies require installation of left- turn lanes at unsignalized median openings in all or most cases. Some agencies stated that left-turn lanes are provided only where specific warrants are met; most respondents indi- cated that their warrants were based on left-turn volumes. Only two agencies responded that they have a formal policy on the conditions under which direct left-turn access to intersections or driveways is replaced by indirect left-turn treatment. TREATMENT OF U-TURNS AT MEDIAN OPENINGS Many state and local transportation agencies install nontra- versable medians on multilane arterial highways to improve safety and travel times, often denying the opportunity for direct left-turn access to certain properties. Traffic destined 28 for such locations must use alternate routes, some of which may involve making U-turns at nearby median openings. Other highway agencies are replacing conventional median openings that allow all traffic movements with directional median openings that allow only U-turn movements or allow only left-turn ingress to abutting developments; the left-turn egress movements would be made by turning right onto the arterial road and then making U-turn maneuvers downstream. Consideration of U-Turn Maneuvers In the survey questionnaire, highway agencies were asked if they have a formal policy for designing and locating median openings that makes specific reference to U-turn maneuvers. Only 16 percent of responding highway agencies indicated that they had a formal policy that addressed U-turn maneuvers. Most of these agencies rely primarily on AASHTO geometric design policies or some variation of AASHTO policy in their own guidelines. The factors mentioned in the policies for U-turn maneuvers at unsignalized median openings include • Median width (based on design vehicles and potential for encroachment); • Traffic conditions, including ADTs, truck volumes, and peak-hour turning movement counts; • Sight distance; • Ability to begin and end U-turn maneuvers on the inner lane next to the median; • Accident frequency, particularly angle and rear-end col- lisions involving left- or U-turning vehicles; • Specific threshold accident history criteria, such as five or more left-turn or U-turn-related accidents per year, similar to MUTCD requirements; • Location of the median openings with respect to signal- ized intersections; • Presence of exclusive left-turn lanes; and • Availability of alternate locations for left- and U-turn maneuvers. Prohibition of U-Turn Maneuvers Highway agencies were asked whether U-turn maneuvers were permitted or not permitted at the following types of median openings: • Median openings on rural highways, • Median openings on urban/suburban arterials, Agency type Number of questionnaires mailed Number of responses received Response rate (%) State agencies 50 35 70.0 Local agencies 109 30 27.6 Total 159 65 40.9 TABLE 10 Response rate for the highway agency survey

• Unsignalized median openings, and • Signalized median openings. Table 13 summarizes the agency responses. Approximately 80 percent of the agencies that responded permit U-turns at all types of median openings. Nine agencies generally pro- hibit U-turn maneuvers at unsignalized median openings. 29 The agencies with formal policies concerning when to prohibit U-turns at median openings do so in the following situations: • At all signalized intersections that have a right-turn over- lap phase from a side-street approach on the left during the protected left-turn phase on the mainline roadway; Minimum spacing (ft) State Rural Urban Comments Alabama 600 300 Arizona 1,320 660 For businesses generating high traffic volumes the minimum spacing is 330 ft California 1,640 1,640 Unsure of possible differences between rural and urban criteria Florida 1,320 2,640 330-660 660-1,320 Directional Conventional Georgia 1,320 660 Maximum spacing 5,200 ft in rural areas and 1,320 ft in urban areas Iowa 1,000 660 Idaho 1,312 660 Illinois 2,625 (minimum) 5,250 (desirable) 1,312 Longer minimum spacing used if needed to accommodate left turn lanes Louisiana 1,500 500 Maine – 1,312-1,640 (minor arterial) 1,640-1,968 (major arterial) Criteria apply to signalized median openings only Michigan 1,320 660 Desirable spacing Mississippi 1,760 880 North Carolina 1,500 700 (< 45 mph) 1,000 (45-55 mph) Urban spacing criteria vary with operating speed Nebraska 1,000 (minimum) 2,000 (desirable) 600 New Mexico 600 300 Nevada 660 – In urban areas, have criteria for access spacing rather than median opening spacing Ohio – – Have spacing criteria for driveways but not for median openings Oklahoma 2,640 (minimum) 5,280 (desirable) 1,320 Longer minimum spacing used if needed to accommodate left turn lanes Pennsylvania 1,500 1,500 South Carolina 1,000 500 Texas 1,320 – 2,640 1,320 – 2,640 Virginia 700-1,000 (35-45 mph) 500-650 (50-70 mph) 700-1,000 (35-45 mph) 500-650 (50-70 mph) Urban spacing criteria vary with design speed Range 500 – 2,640 300 – 2,640 Average 1,400 880 TABLE 11 State policies on minimum spacing between median openings

• At any curve or on the approach to or near the crest of a grade where a U-turning vehicle cannot be seen by the driver of any other vehicle approaching from any direc- tion within 150 m (500 ft) and at any intersection that does not meet the minimum sight distance criteria stan- dards for U-turns as established by AASHTO; 30 • At intersections with a receiving pavement width of 7.3 m (24 ft) or less and at which the average vehicle cannot exe- cute a U-turn maneuver in a single continuous movement; • At any location for which a review of accident history finds that a U-turn restriction should be implemented, possibly only for certain times of the day; TABLE 12 Local agency policies on minimum median opening spacing Minimum spacing (ft) County Rural Urban Comments San Diego, CA – 600 Springfield, MO – 500 Fargo, ND – 600 (arterials) 300 (collectors) Concord, NH – 500 (commercial) 1,000 (suburban) For arterials and collectors Henderson, NV – 660 Maricopa County, AZ 660 660 For arterials and collectors Pima County, AZ 1,320 1,320 Riverside County, CA 330-1,320 330-1,320 Based on intersection spacing Osceola County, FL 1,320 2,640 330-660 660-1,320 Directional Conventional Broward County, FL 660 660 Range 660 – 2,640 330 – 1,320 Average 800 725 Number (percentage) of agencies that permit U-turns at specific types of median openings Agency type U-turns permitted U-turns not permitted Total Median Openings on Rural Highways State agencies 26 (83.9) 5 (16.1) 31 Local agenciesa 4 (100.0) 0 (0.0) 4 Total 30 (85.7) 5 (14.3) 35 Median Openings on Urban Highways State agencies 26 (83.9) 5 (16.1) 31 Local agencies 22 (84.6) 4 (15.4) 26 Total 48 (84.2) 9 (15.8) 57 Unsignalized Median Openings State agencies 26 (83.9) 5 (16.1) 31 Local agencies 22 (84.6) 4 (15.4) 26 Total 48 (84.2) 9 (15.8) 57 Signalized Median Openings State agencies 25 (80.6) 6 (19.4) 31 Local agencies 20 (76.9) 6 (23.1) 26 Total 45 (78.9) 12 (21.1) 57 a Includes county agencies only. TABLE 13 Number of highway agencies that permit U-turns at specific types of median openings

• Geometric design criteria; • At signalized intersections; and • If less than 11.3 m (37 ft) of width is available from the inside of the left-turn curb to the curb of the oppos- ing lanes. Two agencies stated that U-turns are prohibited at all median openings unless they are signed to permit U-turns. Some agencies that did not have formal policies on where to permit or prohibit U-turns have informal guidelines that are presented below: • U-turns are permitted only at locations having sufficient roadway width for maneuver. • U-turns are prohibited based on accident rate or safety problems. • U-turns are prohibited at signalized intersections where right-turn overlaps are allowed. • U-turns are prohibited where they would create a sub- stantial number of conflicts. 31 • U-turns are prohibited in some school zones. • U-turns are prohibited to relieve congestion at median openings. • U-turns are permitted at unsignalized median openings where a specific need is identified. • U-turns are prohibited where a need is identified through engineering judgment. MEDIAN AND ROADWAY WIDTHS TO ACCOMMODATE U-TURN MANEUVERS The minimum median and roadway widths required to accommodate U-turn vehicles are key factors in whether a U-turn movement is permitted at a median opening. About half of the responding agencies stated that they follow the AASHTO Green Book (3) to determine the median and road- way widths required to provide for U-turns at unsignalized median openings. Figure 13 illustrates these AASHTO crite- ria, based on Green Book Exhibit 9-92. Several agencies Figure 13. AASHTO minimum median widths to accommodate U-turns (3).

stated that they have no policy or use engineering judgment. The remaining agencies that responded have specific policies that differ from AASHTO Green Book; these policies are summarized below: • Minimum median widths wider than those presented in the Green Book are used. • U-turns are permitted on roads with a minimum width of six lanes. • Minimum median widths in the range of 3 to 6 m (10 to 20 ft), based on the type of roadway, are used. • U-turns are permitted on arterials with a minimum width of 12.8 m (42 ft), which includes a 1.2-m (4-ft) separa- tor, 10 m (33 ft) of travel lane width, and 1.5 m (5 ft) of bike lane width. • U-turns are permitted with a median width of 4.3 m (14 ft) and roadway width for one direction of travel of 7.9 m (26 ft). • U-turns are permitted with a median width between 6 and 7 m (20 and 24 ft) and directional roadway width between 9 and 11 m (30 and 36 ft) for a four-lane divided highway. When asked whether their criteria for design of median openings included provisions for U-turns by large vehicles (e.g. school buses, other buses, or large trucks), approximately one-half of the responding state agencies and one local agency indicated that such provisions are made. TRAFFIC OPERATIONAL AND SAFETY PROBLEMS AT MEDIAN OPENINGS Several factors affect the safety and operational perfor- mance of a median opening, e.g., • Degree of urbanization, • Operating speeds, • Access density, • Roadway geometrics, • Traffic volumes, • Physical constraints, and • Median width. For example, it is well known that locations with fewer con- flict points (i.e., where fewer traffic movements cross one another) are likely to experience fewer accidents than loca- tions with more conflict points. Thus, it is likely that a median opening that serves U-turns only will operate more safely than one where U-turns use the same roadway as left-turn and crossing maneuvers. Similarly, a median opening that serves only one intersection or driveway would function like a three- leg intersection and would likely operate more safely than a median opening that serves intersection legs or driveways on both sides of the arterial roadway, which would function like a four-leg intersection. 32 Highway agencies were asked whether they had experi- enced safety or traffic operational problems at unsignalized median openings. Nearly 60 percent of the agencies that responded indicated that they had. The five most cited fac- tors related to safety or operational problems at unsignalized median openings in decreasing order are as follows: • Operational considerations (e.g., heavy U-turns or through volumes, and trucks), • Median too narrow, • Driveway nearby, • Poor roadway geometry, and • Roadway too narrow. A more complete list of factors identified by highway agen- cies as related to the safety or operational problems they encountered at unsignalized median openings is presented in Appendix B. MITIGATION MEASURES FOR SAFETY PROBLEMS When asked if they have constructed improvement proj- ects intended to mitigate safety and operational problems at unsignalized median openings, 37 percent of responding high- way agencies indicated they have constructed improvement projects. Some of the mitigation measures for safety and operational problems cited are as follows: • Removal of closely spaced median openings by replac- ing raised medians with TWLTLs; • Replacement of conventional crossovers with directional crossovers; • Installation of left-turn storage lanes; • Installation of left-turn lanes with positive offset; • Signalized intersections; • Closure of median openings to allow left turns to align properly; • Reconfiguring of median openings by channelizing or adding left-turn lanes to prevent congestion or confu- sion in the median opening; • Installation of directional median openings to permit left turns from the major-road left-turn lane, but prohibit left turns and through movements from the minor road; • Provision of a median opening at what formerly was a right-in/right-out driveway; • Elimination of conventional median openings and replacement with jughandle U-turns; • Installation of “No U-turn” signs; and • Installation of raised/extended median to prevent U-turns. Six of the agencies that constructed improvement projects indicated that they have conducted a formal before-and-after evaluation.