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62 TABLE 21 Number of median Median Opening Types Included openings by shoulder type in Data Collection and Analysis Shoulder Number of type sites Based on the catalog of median opening designs that are Paved 480 (59.8) representative of what actually exists in the field, the follow- Curb 244 (30.3) ing median opening designs were given highest priority in Mountable curb 21 (2.6) the accident and field studies: Other 56 (6.9) No shoulder 5 (0.6) Total 806 Type 1a = Conventional midblock median opening with- out left-turn lanes Type 1b = Conventional midblock median opening with left-turn lanes Median Type and Width Type 2b = Directional midblock median opening with left-turn lanes The type and width of median at each of the unsignalized Type 2c = Directional midblock median opening with median openings was noted during the site visits. Of the 806 left-turn lanes and loons unsignalized median openings, 502 median openings (62 per- Type 3a = Conventional median opening without left- cent) were located at raised medians, 303 median openings turn lanes at three-leg intersection (38 percent) were located at depressed medians, and one Type 3b = Conventional median opening with one left- median opening was located at a paved median. About one- turn lane at three-leg intersection third of the median openings were 6 m (20 ft) wide or less; Type 3c = Conventional median opening with two left- about one-third were between 6 and 12 m (20 and 40 ft) wide; turn lanes at three-leg intersection and about one-third were greater than 12 m (40 ft) wide. Type 4a = Directional median opening for left turns from major road at three-leg intersection Type 5a = Conventional median opening without left- U-Turn Potential turn lanes at four-leg intersection Type 5b = Conventional median opening with left-turn At each unsignalized median opening, research team mem- lanes at four-leg intersection bers estimated the potential for U-turn activity at that site, Type 6a = Directional median opening for left turns based on the surrounding development or actual U-turn activ- from major road at four-leg intersection ity observed. Table 22 presents the distribution of U-turn potential by median opening type. These median opening designs appeared to be most com- monly used by highway agencies and/or were most promising in terms of safety performance. The preceding list includes median opening Type 2c, directional midblock median open- TABLE 22 Number of median openings ing with left-turn lanes and loons. The usage of loons was by U-turn potential and median opening type observed in four of the states visited in the catalog process Median opening U-turn potential (i.e., Georgia, Kansas, Michigan, and New York). Therefore, type Low High they were included in the accident and field studies to assess Midblock 1a 21 (4.6) 19 (5.4) their appropriateness for wider use. 1b 13 (2.9) 9 (2.6) 1c 2 (0.4) 4 (1.1) 2a 0 (0.0) 1 (0.3) 2b 2 (0.4) 147 (41.8) DATA COLLECTION AND ANALYSIS 2c 1 (0.2) 16 (4.5) FOR SELECTED MEDIAN OPENINGS Three-leg 3a 79 (17.4) 23 (6.5) Three major data collection and analysis activities were 3b 64 (14.1) 27 (7.7) conducted in the research: 3c 54 (11.9) 24 (6.8) 3d 2 (0.4) 7 (2.0) Field observational studies of existing median openings 4a 12 (2.6) 12 (3.4) used for U-turns, Four-leg 5a 76 (16.7) 18 (5.1) Accident studies of existing median openings used for 5b 120 (26.4) 39 (11.1) U-turns, and 6a 8 (1.8) 6 (1.7) Analysis of traffic conflicts and driver behavior at median Total 454 352 openings used for U-turns.

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63 The following discussion provides an overview of each of flicts or undesirable driving behavior to be reviewed and these data collection and analysis efforts. The findings of classified from more than one angle. The quadrants chosen those analyses are presented in Chapter 6. for camera locations varied from site to site to obtain the best viewing angles. The video cameras were equipped with char- acter generators with the capability of superimposing an Field Observational Studies elapsed time to the nearest 0.1 sec on the recorded video of Existing Median Openings image to document the precise time at which events of inter- Field observational studies were conducted at four corri- est occurred. dors in each of the following five geographic regions, for a In addition to the one field observational study per corridor, total of 20 corridors: short 15- to 30-min turning movement counts were performed at other median openings in the corridor during the same West (Colorado), period as the video studies. These counts were scaled up to the Midwest (Kansas/Missouri), full period of the video study using the traffic count data from North (Michigan), the videotapes for the primary study site in the same corridor. South (Georgia), and These additional volume counts (including U-turn volumes) Northeast (New Jersey/New York). allowed for better use of the accident data for those other median openings. Table 24 presents the number of median The corridors were selected on the basis of median open- openings, by median opening type and geographic region, at ing types and level of U-turn activity. Within each corridor, which turning movement counts were obtained, either from one intersection was selected for videotaping on the basis of the videotapes or from supplemental manual counts. the data already collected during the catalog process and a To supplement the information on individual median open- further field review of the site. The intersections selected for ings obtained during the catalog process, the following site videotaping were selected to cover the range of median open- characteristics were documented during the field observa- ing types and median widths of interest to the study. tional studies: The field observational studies involved videotaping one unsignalized median opening in each arterial corridor for peri- Median opening dimensions (i.e., length and width), ods of approximately 6 hours per site, including the evening Distance to nearest intersection, peak period and two off-peak periods. Table 23 presents the Distance to nearest signal, number of videotaped median openings in each geographic Distance to nearest driveway, region by median opening type. Character of surrounding development, and The videotapes were used for two purposes: (1) to obtain Level of pedestrian activity. counts of turning movement volumes at the intersections and (2) to note traffic conflicts and undesirable driving behavior Documentation obtained in the field included photographs of that may be indicators of safety problems at the median open- specific median opening types. ing. From the turning movement counts, typical U-turn vol- umes (and percentage of total turning volumes) for median openings with various designs were determined. Data on traf- Accident Studies of Existing Median Openings fic conflicts and undesirable driving behavior were used in the human factors evaluation. Accident data, including data on the characteristics of each Figure 46 illustrates the field setup used in the study, with individual traffic accident at or related to the median open- video cameras in two different quadrants of the intersection. ings of interest, were obtained from the participating high- This setup provided good viewing angles for all turning way agencies. Then, accident studies of existing median open- movements at the intersection and allowed any traffic con- ings were conducted to learn the following: TABLE 23 Number of videotaped median openings (by median opening type) in each geographic region Median opening type Geographic region 1a 1b 2b 2c 3a 3b 3c 4a 5a 5b 6a Total West (CO) 1 1 2 4 Midwest (KS/MO) 1 1 2 2 1 7 North (MI) 8 4 12 South (GA) 1 1 2 Northeast (NJ/NY) 1 2 2 1 1 7 Total 1 8 5 1 5 1 3 2 5 1 32 NOT E : Michigan sample sizes are larger than other states because the study sites were pairs of directional median openings rather than single bidirectional median openings.

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64 Figure 46. Typical data collection setup using video cameras (8). Traffic accident frequencies and rates for median open- Complete accident data were not available for every study ings of various types, corridor. A few of the corridors were not state-maintained Relationship of U-turn volumes to median opening acci- and, therefore, the accident data for some of these corridors dent rates, and were either unavailable or were incomplete. The accident Pattern of accident types and severities at median open- descriptors that were obtained are as follows: ings with substantial U-turn volumes and at median open- ings with relatively few U-turns. Accident location (milepost or other information that identifies the location of accidents with respect to the median openings of interest), Accident Data Relationship to junction (at intersection/not at intersec- Accident data were obtained from each of the partici- tion, but intersection related), pating highway agencies for the selected corridors for a Accident date, period of at least 4 years. The periods for which accident data Time of day, were obtained for median opening sites in each state were as Accident severity, follows: Light condition (day and night), Pavement surface condition (i.e., dry/wet/ice and snow), Colorado (19972001) Accident type/manner of collision, Georgia (19972001) Initial direction of travel of involved vehicles, Kansas (19972001) Intended maneuvers of involved vehicles (i.e., straight Michigan (19931997) ahead/right turn/left turn/U-turn), Missouri (19972001) Vehicle types of involved vehicles (e.g., passenger car/ New Jersey (19972000) bus/truck/RV), and New York (19962001) First harmful event/most harmful event. TABLE 24 Number of median openings (by median opening type) in each geographic region at which turning movement counts were obtained Median opening type Geographic region 1a 1b 2b 2c 3a 3b 3c 4a 5a 5b 6a Total West (CO) 7 5 10 1 23 Midwest (KS/MO) 1 2 2 5 3 13 North (MI) 21 10 1 32 South (GA) 1 12 1 1 12 27 Northeast (NJ/NY) 1 1 4 9 1 3 6 5 30 Total 2 1 22 14 3 30 2 9 5 31 6 125

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65 For median openings at intersections, the project database openings whose U-turn volumes are known and those whose includes all accidents identified by the investigating officer or U-turn volumes are not known. by data coding as related to that intersection. For intersections not at median openings, all accidents within 75 m (250 ft) of the median opening are included in the database. Where acci- Accident Distributions dent locations could not be tied accurately to a specific median opening (which occurred at midblock locations for some Out of a total of 7,717 median-opening-related accidents, agencies), that particular median opening was dropped from only 79 accidents (1.1%) were identified as involving U-turns. the project database. Because this did not appear to be a sufficient number of U-turn accidents to draw useful conclusions about the safety performance of median openings, a decision was made to Traffic Volume Data include both U-turn and left-turn accidents in the analyses. Review of the accident data indicated that many U-turn acci- Traffic volume data and turning movement counts, where dents are, in fact, coded as left-turn accidents. Specifically, available, were obtained from the files of the participating at some nonintersection median openings, where all move- agencies. Where traffic volume data were not available for a ments through the median opening are, by definition, U-turns, set of median openings in a corridor, the research team (1) per- many accidents are coded as left-turn accidents. The database formed turning movement counts (including counts of U-turn included 79 U-turn accidents (1.1%) and 1,293 left-turn acci- maneuvers) for at least one median opening in the corridor and dents (16.8%) for a total of 1,372 U-turn-plus-left-turn acci- (2) estimated the traffic volumes for the other median open- dents (17.8%). ings in the corridor based on observations of the general level Tables 25 through 27 present accident frequencies by of turning activity (i.e., high, medium, and low) and com- median opening type, number of legs, and intersection geom- parison of the relative access point densities of the median etry, respectively. U-turn and left-turn accidents are presented TABLE 25 Distribution of accidents by median opening type Number of accidents Percentage of total accidents Median No. of U-turn U-turn opening median and and type openings U-turn Left turn left turn Total U-turn Left turn left turn Midblock 1a 37 4 13 17 185 2.2 7.0 9.2 1b 7 0 6 6 73 0.0 8.2 8.2 2b 145 6 125 131 1,423 0.4 8.8 9.2 2c 10 2 3 5 82 2.4 3.7 6.1 Three-leg 3a 83 2 112 114 640 0.3 17.5 17.8 3b 121 26 253 279 1,367 1.9 18.5 20.4 3c 24 1 35 36 273 0.4 12.8 13.2 4a 21 2 49 51 418 0.5 11.7 12.2 Four-leg 5a 84 4 116 120 750 0.5 15.5 16.0 5b 125 27 458 485 2,044 1.3 22.4 23.7 6a 11 5 123 128 353 1.4 34.8 36.3 TABLE 26 Distribution of accident by number of legs at intersection Number of accidents Percentage of total accidents No. of U-turn U-turn Crossing median and and type openings U-turn Left turn left turn Total U-turn Left turn left turn Midblock 199 12 147 159 1,763 0.7 8.3 9.0 Three-leg 249 31 449 480 2,698 1.1 16.6 17.7 Four-leg 220 36 697 733 3,147 1.1 22.1 23.2

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66 TABLE 27 Distribution of accidents by type of geometry Percentage of total Number of accidents accidents No. of U-turn U-turn Geometry median Left and Left and type openings U-turn turn left turn Total U-turn turn left turn Conventional 481 64 993 1,057 5,332 1.2 18.6 19.8 Directional 187 15 300 315 2,276 0.7 13.2 13.9 separately as well as in combination. The tables shown here length, multiple vehicles making multiple maneuvers will are simply meant to illustrate various distributions of the use the same gap. This situation may be exacerbated accident data and are not intended to present any conclusive as the number of lanes in the cross-section increases, relationships. because the task of finding a gap in three lanes of on- coming traffic (from one direction of travel on the major road) is not a simple task. Given the lack of any formal Analysis of Traffic Conflicts priority scheme for the performance of these different and Driver Behavior at Existing Median Openings maneuvers, drivers will cut off other drivers, hesitate in The videotapes recorded during the field data collection initiating or completing their maneuver, or take a cir- effort were reviewed to document how drivers behave in mak- cuitous path in completing their maneuver. ing U-turns and left turns through unsignalized median open- Drivers make a "discontinuous" U-turn--The cross- ings. Approximately, 152 hours of videotapes from 26 urban section configuration [primarily the combination of the sites were reviewed. In general, seven types of undesirable median and the opposite (major) roadway] is such that driving behavior, or unsafe driving conditions, were observed. there is not enough area to accommodate the turning Each one is presented below, followed by a discussion of the radius of the vehicle. The compensating behavior by the causes of that behavior. driver is to shift the vehicle into reverse, turn the wheels to redirect the vehicle, shift the vehicle back to drive, Vehicles slow in response to turning vehicle(s)--The and complete the U-turn (or what is often called a "K" median geometry is such that there is no deceleration or 3-Point-turn). lane or storage area for a vehicle making a left turn or Drivers make a turn not served by the design of the U-turn so that the deceleration of the turning vehicle must intersection--Some median openings are designed to take place in the through travel lane (major roadsame accommodate only a limited number of turn maneuvers direction). The median may also be of insufficient width (e.g., left in, but not left out). Drivers proceeding from the to store the vehicle once it has slowed or stopped, which minor roadway (or driveway) attempt (and usually com- can lead to other problems. This problem is exacerbated plete) a left turn through a median opening not designed for trucks. for such a maneuver. This may be result from a lack of Vehicles queue in response to turning vehicle(s)--The knowledge of where the driver may be allowed to direct median geometry, or the lack of sufficient gaps of ade- his vehicle to the opposite side of the major road. This quate length in the opposing traffic stream (major road), behavior also could result from a sense of frustration is such that when one (or multiple) vehicles attempt to because the driver could enter the minor roadway (or turn, the queue spills back into the through travel lane driveway) from the major roadway by performing a left (major road--same direction). This problem is exacer- turn, but cannot "re-enter" that same roadway by again bated for trucks. performing a left turn. Vehicles drive in the wrong direction in the median-- Drivers hesitate when entering the median roadway-- For locations where there is a raised median separating Drivers will hesitate when entering the median roadway the directional flows of traffic on the median roadway, when they are unsure of what maneuver a driver already drivers sometimes drive in the wrong direction on the in the median roadway is attempting. For example, if a median roadway. This may be because of poor median driver entering the median roadway from the major road opening design, which confuses the driver or because of is attempting to make a U-turn and a second driver enter- total disregard for the general rules of the road where the ing the median roadway from the major road (opposite driver recognizes the proper operation of the opening direction) is attempting a left turn maneuver, the second but decides to perform an undesirable maneuver despite driver may not understand the intention of the first the cues presented at the opening. driver and does not know whether to turn "in front of" or Drivers making turns use the same gap--For loca- "behind" the first vehicle. The driver of the second vehi- tions where there is a lack of adequate gaps of sufficient cle hesitates and waits in the through lane of the major

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67 road (opposite direction) until able to ascertain the Conflict Type B: Conflict between two or more vehicles driver of the first vehicle's intended maneuver. within the median opening. This conflict type includes the following undesirable driving behaviors: (1) vehicles For purposes of conducting a traffic conflict analysis, the drive in the wrong direction in the median and (2) drivers seven types of undesirable driver behavior were grouped into make a turn not served by the design of the intersection. three conflict types: Conflict Type C: A vehicle turning from the median opening onto the major road causes the vehicle on the Conflict Type A: A vehicle turning from the major road major road to brake. This conflict type includes the fol- into the median opening causes the following vehicle on lowing undesirable driving behaviors: (1) drivers mak- the major road to brake. This conflict type includes the ing turns use the same gap and (2) drivers make a "dis- following undesirable driving behaviors: (1) vehicles continuous" U-turn. slow in response to turning vehicle, (2) vehicles queue up in response to turning vehicle, and (3) drivers hesi- Table 28 summarizes the traffic conflict data collected dur- tate when entering the median roadway. ing the videotape studies. TABLE 28 Summary of data for traffic conflict analysis Turning counts Number of Number of conflicts by conflict type conflicts 3 Total Major- Major- Minor- Total Number (per 10 hours of road road road major-road of turning a b c Type videotape U-turn left turn left turn volume conflicts vehicles) A B C URBAN ARTERIAL CORRIDORS Midblock 2b 24 2,103 0 0 50,367 6 2.9 1 0 5 2c 29 1,746 0 0 72,351 36 20.6 0 1 35 Three-leg 3b 36 758 888 221 63,472 12 6.4 4 2 6 4a 21 546 524 192 52,469 43 34.1 6 0 37 Four-leg 5a 12 424 568 493 27,713 19 12.8 17 2 0 5b 24 689 1,792 565 68,721 31 10.2 7 5 19 6a 6 421 303 0 19,814 20 27.6 1 0 19 a Conflict Type A: Vehicle turning from the major road into the median opening causes following vehicle on the major road to brake. b Conflict Type B: Conflict between two or more vehicles within the median opening. c Conflict Type C: Vehicle turning from the median opening onto the major road causes vehicle on the major road to brake.