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

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59 CHAPTER 5 DATA COLLECTION AND ANALYSIS This chapter describes the data collection and analysis efforts conducted as part of the research. The major efforts were a catalog of existing median openings, accident studies of existing median openings, field observational studies of existing median openings, and human factors evaluation of driver behavior in U-turn maneuvers. CATALOG OF EXISTING MEDIAN OPENINGS The first activity of the data collection effort was to create a catalog of median opening designs representative of what actually exists in the field. The first task in the creation of a catalog was to identify arterial corridors that include median openings. The second task was visiting the corridors and col- lecting data on the types of median opening designs. This section describes the process of creating a catalog of existing median openings and summarizes the catalog data. Identification of Corridors To identify corridors, the research team contacted highway engineers in five states and requested a list of arterial corri- dors that include median opening designs representative of that state. The states contacted were as follows: • Colorado, • Georgia, • Michigan, • New Jersey, and • New York. A list of approximately 10 to 20 corridors of varying lengths was obtained from each state. In Georgia, all of the corridors were located in Gwinnett County and are under the jurisdic- tion of that county. In the other states, the corridors were under the jurisdiction of the state highway agency and were located in several counties in each state. The research team also identified, through personal experience and the use of state highway maps, corridors within the states of Kansas and Missouri. Overall, corridors were identified in seven states throughout the country for collection of detailed information for cataloging purposes. Collection of Catalog Data Each corridor was visited in the field to collect the follow- ing information on individual median openings: • Location of median opening (milepost or odometer reading), • Cross street name, • Type of traffic control, • Type of median opening, • U-turn prohibition, • Area type (urban/suburban), • Posted speed limit, • Number of through lanes, • Presence of left-turn lanes, • Presence of offset left-turn lanes, • Shoulder type, • Median type, • Median width, • Presence of loon, and • Level of U-turn activity. For each unsignalized median opening, the median opening type was classified according to the categories established in Chapter 4 of this report. Summary of Catalog Data This section presents a detailed summary of the unsignal- ized median openings included in the catalog. Specifically, the distribution of unsignalized median openings by state, median opening type, posted speed limit, number of through lanes, presence of special left-turn treatment, shoulder type, median width and type, and level of U-turn activity are presented. The catalog consisted of 62 arterial corridors in seven states. The corridors comprised a total length of 552 km (343 mi) of arterial highway, or an average of 8.9 km (5.5 mi) per corri- dor. Data were recorded for 918 unsignalized median open- ings located in the 62 arterial corridors. Not all sites, however, were included in the tables presented below. For example, 14 of the unsignalized median openings did not fit into any of the median opening types as outlined in Chapter 4. Also, U-turns were prohibited at 102 of the unsignalized median openings; given that U-turn maneuvers are the focus of the research,

those median openings were not included in the tables pre- sented below. Finally, four median openings had five-lane cross-sections (i.e., three through lanes in one direction of travel and two in the other). Given that the focus of the acci- dent and field studies was on unsignalized median openings on four-lane and six-lane cross-sections, the four five-lane sites were not included in the tables presented below. Thus, 806 unsignalized median openings are included in the tables. State Table 16 lists the number of unsignalized median openings visited in each state. The distribution of sites by state provided a good geographical diversity for accident and field studies. Median Opening Type Based on the classification of median opening types pre- sented in Chapter 4, there are a total of 17 typical median opening design as follows: • 1a = Conventional midblock median opening without left-turn lanes • 1b = Conventional midblock median opening with left- turn lanes • 1c = Conventional midblock median opening with left- turn lanes and loons • 2a = Directional midblock median opening without left- turn lanes • 2b = Directional midblock median opening with left- turn lanes • 2c = Directional midblock median opening with left- turn lanes and loons • 3a = Conventional median opening without left-turn lanes at three-leg intersection • 3b = Conventional median opening with one left-turn lane at three-leg intersection • 3c = Conventional median opening with two left-turn lanes at three-leg intersection 60 • 3d = Conventional median opening with left-turn lanes and loons at three-leg intersection • 4a = Directional median opening for left turns from major road at three-leg intersection • 4b = Directional median opening for left turns onto major road at three-leg intersection • 5a = Conventional median opening without left-turn lanes at four-leg intersection • 5b = Conventional median opening with left-turn lanes at four-leg intersection • 6a = Directional median opening for left turns from major road at four-leg intersection • 7a = Midblock jughandle to the left for U-turn maneuvers • 7b = Midblock jughandle to the right for U-turn maneuvers Table 17 presents the frequency of unsignalized median openings by median opening type. Table 18 presents the num- ber of unsignalized median openings by state and median opening type. Posted Speed Limit Table 19 presents the distribution of sites by posted speed limit and median opening type. The table illustrates a bal- ance between high-speed and low-speed arterials overall, with 43 percent of all median openings located on low-speed arterials and 57 percent located on high-speed arterials. State Number of median openings (%) Colorado 61 (8) Georgia 150 (19) Kansas 137 (17) Michigan 244 (30) Missouri 111 (14) New Jersey 62 (8) New York 41 (5) Total 806 TABLE 16 Number of unsignalized median openings by state Median opening type Number of median openings (%) Midblock 1a 40 (5.0) 1b 22 (2.7) 1c 6 (0.7) 2a 1 (0.1) 2b 149 (18.5) 2c 17 (2.1) Three-leg 3a 102 (12.7) 3b 91 (11.3) 3c 78 (9.7) 3d 9 (1.1) 4a 24 (3.0) 4b 0 (0.0) Four-leg 5a 94 (11.7) 5b 159 (19.7) 6a 14 (1.7) Jughandle 7a 0 (0.0) 7b 0 (0.0) Total 806 (100.0) TABLE 17 Number of unsignalized median openings by median opening type

Cross-Section Table 20 presents the distribution of sites by cross section and median opening type. Most of the arterial corridors rec- ommended to the research team by highway agencies were four-lane arterials; about 10 percent of the sites are located on six-lane arterials. Special Left-Turn Treatments When conducting the site visits, the research team mem- bers noted the presence of offset left-turn lanes, loons, and dual left-turn lanes. These special left-turn treatments will be considered in the accident and field studies because they can influence the safety of an unsignalized median opening. Off- 61 set left-turn lanes provide improved sight distance; loons pro- vide extra pavement width for U-turn vehicles with a large turning radius; and dual left-turn lanes can be confusing to some drivers. Of the 806 unsignalized median openings, 79 had offset left-turn lanes, 34 had loons, and 3 had dual left-turn lanes. Shoulder Type The type of shoulder provided at each of the unsignalized median openings was noted during the site visits. Table 21 presents the distribution of sites by shoulder type. Most of the median openings had paved shoulders. TABLE 18 Number of unsignalized median openings by state and median opening type Median opening type Posted speed limit Low speed (≤ 50 mph) High speed (≥ 55 mph) Midblock Three-leg Four-leg 1a 1b 1c 2a 2b 2c 3 8 3 0 26 8 (0.9) 37 (8.0) (2.3) 14 (3.0) (0.9) 3 (0.7) (0.0) 1 (0.2) (7.5) 123 (26.7) (2.3) 9 (2.0) 3a 23 (6.6) 79 (17.2) 3b 69 (19.9) 22 (4.8) 3c 38 (11.0) 40 (8.7) 3d 9 (2.6) 0 (0.0) 4a 23 (6.6) 1 (0.2) 5a 20 (5.8) 74 (16.1) 5b 105 (30.3) 54 (11.7) 6a 11 (3.2) 3 (0.7) Total 346 460 TABLE 19 Number of median openings by posted speed limit and median opening type Major-road cross-section Median opening type 4-lane 6-lane Midblock 1a 40 (5.5) 0 (0.0) 1b 21 (2.9) 1 (1.2) 1c 6 (0.8) 0 (0.0) 2a 1 (0.1) 0 (0.0) 2b 140 (19.4) 9 (10.6) 2c 12 (1.7) 5 (5.9) Three-leg 3a 102 (14.1) 0 (0.0) 3b 77 (10.7) 14 (16.5) 3c 68 (9.4) 10 (11.8) 3d 9 (1.2) 0 (0.0) 4a 7 (1.0) 17 (20.0) Four-leg 5a 94 (13.0) 0 (0.0) 5b 134 (18.6) 25 (29.4) 6a 10 (1.4) 4 (4.7) Total 721 85 TABLE 20 Number of median openings by cross section and median opening type

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

The following discussion provides an overview of each of these data collection and analysis efforts. The findings of those analyses are presented in Chapter 6. Field Observational Studies of Existing Median Openings Field observational studies were conducted at four corri- dors in each of the following five geographic regions, for a total of 20 corridors: • West (Colorado), • Midwest (Kansas/Missouri), • North (Michigan), • South (Georgia), and • Northeast (New Jersey/New York). The corridors were selected on the basis of median open- ing types and level of U-turn activity. Within each corridor, one intersection was selected for videotaping on the basis of the data already collected during the catalog process and a further field review of the site. The intersections selected for videotaping were selected to cover the range of median open- ing types and median widths of interest to the study. The field observational studies involved videotaping one unsignalized median opening in each arterial corridor for peri- ods of approximately 6 hours per site, including the evening peak period and two off-peak periods. Table 23 presents the number of videotaped median openings in each geographic region by median opening type. The videotapes were used for two purposes: (1) to obtain counts of turning movement volumes at the intersections and (2) to note traffic conflicts and undesirable driving behavior that may be indicators of safety problems at the median open- 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- fic conflicts and undesirable driving behavior were used in the human factors evaluation. Figure 46 illustrates the field setup used in the study, with video cameras in two different quadrants of the intersection. This setup provided good viewing angles for all turning movements at the intersection and allowed any traffic con- 63 flicts or undesirable driving behavior to be reviewed and classified from more than one angle. The quadrants chosen 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 elapsed time to the nearest 0.1 sec on the recorded video image to document the precise time at which events of inter- est occurred. In addition to the one field observational study per corridor, short 15- to 30-min turning movement counts were performed at other median openings in the corridor during the same period as the video studies. These counts were scaled up to the full period of the video study using the traffic count data from the videotapes for the primary study site in the same corridor. These additional volume counts (including U-turn volumes) allowed for better use of the accident data for those other median openings. Table 24 presents the number of median openings, by median opening type and geographic region, at which turning movement counts were obtained, either from the videotapes or from supplemental manual counts. To supplement the information on individual median open- ings obtained during the catalog process, the following site characteristics were documented during the field observa- tional studies: • Median opening dimensions (i.e., length and width), • Distance to nearest intersection, • Distance to nearest signal, • Distance to nearest driveway, • Character of surrounding development, and • Level of pedestrian activity. Documentation obtained in the field included photographs of specific median opening types. Accident Studies of Existing Median Openings Accident data, including data on the characteristics of each individual traffic accident at or related to the median open- ings of interest, were obtained from the participating high- way agencies. Then, accident studies of existing median open- ings were conducted to learn the following: 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 NOTE: Michigan sample sizes are larger than other states because the study sites were pairs of directional median openings rather than single bidirectional median openings. TABLE 23 Number of videotaped median openings (by median opening type) in each geographic region

• Traffic accident frequencies and rates for median open- ings of various types, • Relationship of U-turn volumes to median opening acci- dent rates, and • Pattern of accident types and severities at median open- ings with substantial U-turn volumes and at median open- ings with relatively few U-turns. Accident Data Accident data were obtained from each of the partici- pating highway agencies for the selected corridors for a period of at least 4 years. The periods for which accident data were obtained for median opening sites in each state were as follows: • Colorado (1997–2001) • Georgia (1997–2001) • Kansas (1997–2001) • Michigan (1993–1997) • Missouri (1997–2001) • New Jersey (1997–2000) • New York (1996–2001) 64 Complete accident data were not available for every study corridor. A few of the corridors were not state-maintained and, therefore, the accident data for some of these corridors were either unavailable or were incomplete. The accident descriptors that were obtained are as follows: • Accident location (milepost or other information that identifies the location of accidents with respect to the median openings of interest), • Relationship to junction (at intersection/not at intersec- tion, but intersection related), • Accident date, • Time of day, • Accident severity, • Light condition (day and night), • Pavement surface condition (i.e., dry/wet/ice and snow), • Accident type/manner of collision, • Initial direction of travel of involved vehicles, • Intended maneuvers of involved vehicles (i.e., straight ahead/right turn/left turn/U-turn), • Vehicle types of involved vehicles (e.g., passenger car/ bus/truck/RV), and • First harmful event/most harmful event. Figure 46. Typical data collection setup using video cameras (8). 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 TABLE 24 Number of median openings (by median opening type) in each geographic region at which turning movement counts were obtained

For median openings at intersections, the project database includes all accidents identified by the investigating officer or 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- dent locations could not be tied accurately to a specific median opening (which occurred at midblock locations for some agencies), that particular median opening was dropped from the project database. Traffic Volume Data Traffic volume data and turning movement counts, where available, were obtained from the files of the participating agencies. Where traffic volume data were not available for a set of median openings in a corridor, the research team (1) per- formed turning movement counts (including counts of U-turn maneuvers) for at least one median opening in the corridor and (2) estimated the traffic volumes for the other median open- ings in the corridor based on observations of the general level of turning activity (i.e., high, medium, and low) and com- parison of the relative access point densities of the median 65 openings whose U-turn volumes are known and those whose U-turn volumes are not known. Accident Distributions Out of a total of 7,717 median-opening-related accidents, only 79 accidents (1.1%) were identified as involving U-turns. 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 include both U-turn and left-turn accidents in the analyses. Review of the accident data indicated that many U-turn acci- dents are, in fact, coded as left-turn accidents. Specifically, at some nonintersection median openings, where all move- ments through the median opening are, by definition, U-turns, many accidents are coded as left-turn accidents. The database included 79 U-turn accidents (1.1%) and 1,293 left-turn acci- dents (16.8%) for a total of 1,372 U-turn-plus-left-turn acci- dents (17.8%). Tables 25 through 27 present accident frequencies by median opening type, number of legs, and intersection geom- etry, respectively. U-turn and left-turn accidents are presented Number of accidents Percentage of total accidents Median opening type No. of median openings U-turn Left turn U-turn and left turn Total U-turn Left turn U-turn and 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 Number of accidents Percentage of total accidents Crossing type No. of median openings U-turn Left turn U-turn and left turn Total U-turn Left turn U-turn and 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 TABLE 25 Distribution of accidents by median opening type TABLE 26 Distribution of accident by number of legs at intersection

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

road (opposite direction) until able to ascertain the driver of the first vehicle’s intended maneuver. For purposes of conducting a traffic conflict analysis, the seven types of undesirable driver behavior were grouped into three conflict types: • Conflict Type A: A vehicle turning from the major road into the median opening causes the following vehicle on the major road to brake. This conflict type includes the following undesirable driving behaviors: (1) vehicles slow in response to turning vehicle, (2) vehicles queue up in response to turning vehicle, and (3) drivers hesi- tate when entering the median roadway. 67 • Conflict Type B: Conflict between two or more vehicles within the median opening. This conflict type includes the following undesirable driving behaviors: (1) vehicles drive in the wrong direction in the median and (2) drivers make a turn not served by the design of the intersection. • Conflict Type C: A vehicle turning from the median opening onto the major road causes the vehicle on the major road to brake. This conflict type includes the fol- lowing undesirable driving behaviors: (1) drivers mak- ing turns use the same gap and (2) drivers make a “dis- continuous” U-turn. Table 28 summarizes the traffic conflict data collected dur- ing the videotape studies. Turning counts Number of conflicts by conflict type Type Total hours of videotape Major- road U-turn Major- road left turn Minor- road left turn Total major-road volume Number of conflicts Number of conflicts (per 103 turning vehicles) Aa Bb Cc 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. TABLE 28 Summary of data for traffic conflict analysis