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34 Figure 14. Conventional midblock median opening. Figure 16. Directional median opening at three-leg intersection. Degree of access served U-turn only (midblock median opening), and the types of turning maneuvers permitted. With these Access on one side (at three-leg intersection), and subdivisions, there are a total of 17 typical median opening Access on two sides (at four-leg intersection); designs. The following discussion presents each of the seven Presence of left-turn lane categories of median openings and the specific designs used No left-turn lane present and for those openings. The discussion of each median opening Left-turn lane present; design includes a figure with a diagram of each median open- Presence of loon ing design and a list of the advantages and disadvantages No loon present and associated with each design. Loon present. Conventional Midblock Median Opening OVERVIEW OF TYPICAL MEDIAN OPENING DESIGNS A conventional midblock median opening permits vehi- Using the first two classification factors (geometry type cles to make U-turns, but does not provide separate channel- and degree of access served), typical median openings can be ized roadways for vehicles making U-turns in opposing classified into the following seven categories: directions. Median openings at midblock locations are appro- priate on arterials where providing for U-turn maneuvers 1. Conventional Midblock Median Opening, between intersections may improve operations at intersec- 2. Directional Midblock Median Opening, tions by reducing the U-turn volumes at those intersections 3. Conventional Median Opening at Three-Leg Intersection, or reducing the amount of out-of-direction travel for vehicles 4. Directional Median Opening at Three-Leg Intersection, trying to reach a destination without direct left-turn access. 5. Conventional Median Opening at Four-Leg Intersection, Conventional median openings are appropriate where U-turn 6. Directional Median Opening at Four-Leg Intersection, volumes are relatively low, such that U-turn vehicles in and opposing directions of travel create minimal interference 7. Midblock Jughandle U-Turn Maneuvers. with one another. The conventional midblock median opening design is fur- These seven categories of median openings can be subdi- ther classified into three subcategories based on the presence vided on the basis of the presence of left-turn lanes or loons of left-turn lanes and/or loons: Figure 15. Conventional median opening at three-leg Figure 17. Conventional median opening at four-leg intersection. intersection.

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35 Figures 19 through 21 illustrate these three median opening designs and their advantages and disadvantages. The pres- ence of left-turn lanes in Types 1b and 1c reduces the poten- tial for rear-end collisions between U-turn vehicles and fol- lowing through vehicles. The presence of loons in Type 1c provides a widening in the pavement to accommodate U-turn movements by larger vehicles, such as emergency vehicles and trucks. Figures 19 through 21 show opposing U-turning maneu- vers passing in front of one another and, thus, not overlap- Figure 18. Directional median opening at four-leg ping or conflicting. Where the opposing U-turns do not over- intersection. lap, there are only four conflict points at each of the median opening types shown in the figures; a more complete discus- sion of conflict points is presented later in this chapter of the Type 1a--Conventional Midblock Median Opening report. In some situations, not well defined at this time, but Without Left-Turn Lanes; clearly a function of the size and shape of the median opening, Type 1b--Conventional Midblock Median Opening With U-turning vehicles may overlap (or turn behind one another). Left-Turn Lanes; and The possibility of these alternative maneuver types may cre- Type 1c--Conventional Midblock Median Opening With ate confusion between drivers making opposing U-turns. Left-Turn Lanes and Loons. This issue is addressed further in the subsequent discussion Type 1a--Conventional Midblock Median Opening Without Left-Turn Lanes Advantages Midblock access is provided for vehicles to (a) make a U-turn and (b) reach driveways on the opposite side of the street. Since only major-road traffic is involved, delays to vehicles making U- turns will be less than where an intersection is present. If U-turn traffic would otherwise proceed downstream to an intersection with a median opening, then this treatment should reduce VMT. Since vehicles making a U-turn only need to enter, but not cross, the opposing roadway, a minimum gap of only 4 to 6 sec will be needed. There are only four conflict points, which is less than at a three-leg or four-leg intersection. Providing median openings for U-turns between intersections reduces the number of turning maneuvers at the intersections. Accident rates at midblock median openings are lower than at three- or four-leg median openings. Disadvantages The absence of left-turn lanes increases potential for rear-end collisions between U-turn vehicles and following through vehicles. U-turn vehicles forced to stop in the median opening may encroach on adjacent lanes and interfere with through traffic. U-turn vehicles entering the through lanes may delay full-speed through traffic. Narrow medians may not provide enough space for larger vehicles to negotiate a U-turn. With no directional island, opposing U-turn vehicles may have to overlap. Figure 19. Advantages and disadvantages of median opening type 1a--conventional midblock median opening without left-turn lanes.

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36 Type 1b--Conventional Midblock Median Opening With Left-Turn Lanes Advantages The presence of left-turn lanes reduces potential for rear-end collisions between U-turn vehicles and following through vehicles. The presence of left-turn lanes mitigates the problem of U-turn vehicles encroaching on adjacent lanes and interfering with through traffic while waiting for a gap in the opposing traffic. Midblock access is provided for vehicles to (a) make a U-turn and (b) reach driveways on the opposite side of the street. Since only major-road traffic is involved, delays to vehicles making U- turns will be less than where an intersection is present. If U-turn traffic would otherwise proceed downstream to an intersection with a median opening, then this treatment should reduce VMT. Since vehicles making a U-turn only need to enter, but not cross, the opposing roadway, a minimum gap of only 4 to 6 sec will be needed. There are only four conflict points, which is less than at a three-leg or four-leg intersection. Providing median openings for U-turns between intersections reduces the number of turning maneuvers at the intersections. Accident rates at midblock median openings are lower than at three- or four-leg median openings. Disadvantages U-turn vehicles entering the through lanes may delay full-speed through traffic. Narrow medians may not provide enough space for larger vehicles to negotiate a U-turn. With no directional island, opposing U-turn vehicles may have to overlap. Figure 20. Advantages and disadvantages of median opening type 1b--conventional midblock median opening with left-turn lanes. of factors that influence the safety and operational perfor- The directional midblock median opening design is further mance of median openings. classified into three subcategories based on the presence of left-turn lanes and/or loons: Directional Midblock Median Opening Type 2a--Directional Midblock Median Opening With- out Left-Turn Lanes; A directional midblock median opening permits vehicles to Type 2b--Directional Midblock Median Opening With make U-turns and provides separate channelized roadways for Left-Turn Lanes; and vehicles making U-turns in opposite directions. Thus, oppos- Type 2c--Directional Midblock Median Opening With ing U-turn vehicles will not overlap. Median openings at mid- Left-Turn Lanes and Loons. block locations are appropriate on arterials where providing for U-turn maneuvers between intersections may improve Figures 22 through 24 illustrate these three median open- operations at intersections by reducing the U-turn volumes at ing designs and their advantages and disadvantages. The those intersections or reducing the amount of out-of-direction presence of left-turn lanes in Types 2b and 2c reduces the travel for vehicles trying to reach a destination without direct potential for rear-end collisions between U-turn vehicles and left-turn access. Directional median openings are appropriate following through vehicles. The presence of loons in Type 2c where U-turn volumes are relatively high, such that U-turn provides a widening in the pavement to accommodate U-turn vehicles in opposing directions of travel would otherwise movements by larger vehicles, such as emergency vehicles interfere with one another. and trucks.

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37 Type 1c--Conventional Midblock Median Opening With Left-Turn Lanes and Loons Advantages Widening on the far side of the turn makes it possible to make a U-turn without stopping or backing and reduces interference between U-turn and through traffic, particularly for large vehicles. Without performing major reconstruction, additional space can be provided to facilitate the larger turning path of commercial vehicles along narrow medians. The presence of left-turn lanes reduces potential for rear-end collisions between U-turn vehicles and following through vehicles. The presence of left-turn lanes mitigates the problem of U-turn vehicles encroaching on adjacent lanes and interfering with through traffic while waiting for a gap in the opposing traffic. Midblock access is provided for vehicles to (a) make a U-turn and (b) reach driveways on the opposite side of the street. Since only major-road traffic is involved, delays to vehicles making U- turns will be less than where an intersection is present. If U-turn traffic would otherwise proceed downstream to an intersection with a median opening, then this treatment should reduce VMT. Providing median openings for U-turns between intersections reduces the number of turning maneuvers at the intersections. Accident rates at midblock median openings are lower than at three- or four-leg median openings. Disadvantages U-turn vehicles entering the through lanes may delay full-speed through traffic. With no directional island, opposing U-turn vehicles may have to overlap. The presence of loons may make snow removal and other maintenance work more difficult. Figure 21. Advantages and disadvantages of median opening type 1c--conventional midblock median opening with left-turn lanes and loons. Conventional Median Opening road and the minor road (or driveway) and where U-turn vol- at Three-Leg Intersection umes are relatively low, such that U-turn vehicles in oppos- ing directions of travel create minimal interference with one A conventional median opening at a three-leg intersec- another. tion permits vehicles on the major road to make U-turn move- The conventional median opening design at a three-leg ments on the major road and left- or right-turning movements intersection is further classified into four subcategories on onto the minor road. Vehicles on the minor road may make the basis of the presence of a left-turn lane and/or loon: left or right turns onto the major road. No separate chan- nelized roadways are provided for vehicles making U-turns in opposing directions. Thus, U-turn vehicles may overlap Type 3a--Conventional Median Opening Without Left- with opposing U-turn or left-turn vehicles. Median open- Turn Lanes at Three-Leg Intersection; ings at three-leg intersections are appropriate along arterial Type 3b--Conventional Median Opening With One roadways at street intersections or driveways to major devel- Left-Turn Lane at Three-Leg Intersection; opments where providing access across the median will not Type 3c--Conventional Median Opening With Two create undesirable safety or traffic operational effects. Con- Left-Turn Lanes at Three-Leg Intersection; and ventional median openings are appropriate where it is desir- Type 3d--Conventional Median Opening With Left- able to allow left-turning movements from both the major Turn Lanes and Loons at Three-Leg Intersection.

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38 Type 2a--Directional Midblock Median Opening Without Left-Turn Lanes Advantages This design prevents overlapping U-turns. Midblock access is provided for vehicles to (a) make a U-turn and (b) reach driveways on the opposite side of the street. Since only major-road traffic is involved, delays to vehicles making U- turns will be less than where an intersection is present. If U-turn traffic would otherwise proceed downstream to an intersection with a median opening, then this treatment should reduce VMT. Since vehicles making a U-turn only need to enter, but not cross, the opposing roadway, a minimum gap of only 4 to 6 sec will be needed. There are only four conflict points, which is less than at a three-leg or four-leg intersection. Providing median openings for U-turns between intersections reduces the number of turning maneuvers at the intersections. Accident rates at midblock median openings are lower than at three- or four-leg median openings. Disadvantages The absence of left-turn lanes increases potential for rear-end collisions between U-turn vehicles and following through vehicles. U-turn vehicles forced to stop in the median opening may encroach on adjacent lanes and interfere with through traffic. U-turn vehicles entering the through lanes may delay full-speed through traffic. Narrow medians may not provide enough space for larger vehicles to negotiate a U-turn. Figure 22. Advantages and disadvantages of median opening type 2a--directional midblock median opening without left-turn lanes. Figures 25 through 28 illustrate these four median opening The first type, designated as Type 4a, permits vehicles to designs and their advantages and disadvantages. The presence turn left off the major road onto the minor road and to make of left-turn lanes in Types 3b, 3c, and 3d reduces the poten- U-turn maneuvers on the major road, but does not permit tial for rear-end collisions between U-turn vehicles and fol- vehicles to turn left from the minor road onto the major road. lowing through vehicles. The presence of loons in Type 3d The second type, designated as Type 4b, permits vehicles to provides a widening in the pavement to accommodate U-turn turn left or right from the minor road onto the major road and movements by larger vehicles, such as emergency vehicles vehicles on the major road to make U-turn maneuvers, but and trucks. does not permit vehicles to turn left off the major road onto the minor road. Median openings at three-leg intersections are appropriate along arterial roadways at street intersections Directional Median Opening at Three-Leg Intersection or driveways to major developments where providing access across the median will not create undesirable safety or traf- There are two types of directional median openings at three- fic operational effects. leg intersections: Directional median openings are appropriate where U-turn or left-turn volumes are relatively high, such that a conven- Type 4a--Directional Median Opening for Left Turns tional median opening would experience considerable inter- from Major Road at Three-Leg Intersection; and ference between vehicles entering the median opening. Direc- Type 4b--Directional Median Opening for Left Turns tional median openings are also appropriate where there is a onto Major Road at Three-Leg Intersection. disproportionately high left-turn demand from either the major

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39 Type 2b--Directional Midblock Median Opening With Left-Turn Lanes Advantages The presence of left-turn lanes reduces potential for rear-end collisions between U-turn vehicles and following through vehicles. The presence of left-turn lanes mitigates the problem of U-turn vehicles encroaching on adjacent lanes and interfering with through traffic while waiting for a gap in the opposing traffic. This design prevents overlapping U-turns. Midblock access is provided for vehicles to (a) make a U-turn and (b) reach driveways on the opposite side of the street. Since only major-road traffic is involved, delays to vehicles making U- turns will be less than where an intersection is present. If U-turn traffic would otherwise proceed downstream to an intersection with a median opening, then this treatment should reduce VMT. Since vehicles making a U-turn only need to enter, but not cross, the opposing roadway, a minimum gap of only 4 to 6 sec will be needed. There are only four conflict points, which is less than at a three-leg or four-leg intersection. Providing median openings for U-turns between intersections reduces the number of turning maneuvers at the intersections. Accident rates at midblock median openings are lower than at three- or four-leg median openings. Disadvantages U-turn vehicles entering the through lanes may delay full-speed through traffic. Narrow medians may not provide enough space for larger vehicles to negotiate a U-turn. Figure 23. Advantages and disadvantages of median opening type 2b--directional midblock median opening with left-turn lanes. road or the minor road and, therefore, either Type 4a or Type opposing directions. Thus, U-turn vehicles may overlap with 4b would accommodate the needs of the intersection. Direc- opposing U-turn or left-turn vehicles. Median openings at tional median openings are desirable where an intersection is four-leg intersections are appropriate along arterial roadways going to be signalized, given that these openings only affect at street intersections or driveways to major developments major-road traffic in one direction and that effective two- where providing access across the median will not create direction signal coordination can be maintained (5). undesirable safety or traffic operational effects. Conventional Figures 29 and 30 illustrate these two median opening median openings are appropriate where it is desirable to designs and their advantages and disadvantages. allow left-turning movements from both the major road and the minor road (or driveway) and where U-turn volumes are relatively low, such that U-turn vehicles in opposing direc- Conventional Median Opening tions of travel create minimal interference with one another. at Four-Leg Intersection The conventional median opening design at a four-leg intersection is further classified into two subcategories based A conventional median opening at a four-leg intersection on the presence of left-turn lanes: permits vehicles on the major road to make U-turn move- ments on the major road and left- or right-turning movements Type 5a--Conventional Median Opening Without Left- onto the minor road. Vehicles on the minor road may make Turn Lanes at Four-Leg Intersection; and left or right turns onto the major road. No separate channel- Type 5b--Conventional Median Opening With Left- ized roadways are provided for vehicles making U-turns in Turn Lanes at Four-Leg Intersection.

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40 Type 2c--Directional Midblock Median Opening With Left-Turn Lanes and Loons Advantages Widening on the far side of the turn makes it possible to make a U-turn without stopping or backing and reduces interference between U-turn and through traffic, particularly for large vehicles. Without performing major reconstruction, additional space can be provided to facilitate the larger turning path of commercial vehicles along narrow medians. The presence of left-turn lanes reduces potential for rear-end collisions between U-turn vehicles and following through vehicles. The presence of left-turn lanes mitigates the problem of U-turn vehicles encroaching on adjacent lanes and interfering with through traffic while waiting for a gap in the opposing traffic. This design prevents overlapping U-turns. Midblock access is provided for vehicles to (a) make a U-turn and (b) reach driveways on the opposite side of the street. Since only major-road traffic is involved, delays to vehicles making U-turns will be less than where an intersection is present. If U-turn traffic would otherwise proceed downstream to an intersection with a median opening, then this treatment should reduce VMT. Providing median openings for U-turns between intersections reduces the number of turning maneuvers at the intersections. Accident rates at midblock median openings are lower than at three- or four- leg median openings. Disadvantages The presence of loons may make snow removal and other maintenance work more difficult. Figure 24. Advantages and disadvantages of median opening Type 2c-- directional midblock median opening with left-turn lanes and loons. Figures 31 and 32 illustrate these two median opening considerable interference between vehicles entering the median designs and their advantages and disadvantages. The pres- opening. This particular directional median opening design ence of left-turn lanes in Type 5b reduces the potential for is also appropriate where there is a disproportionately high rear-end collisions between U-turn vehicles and following left-turn demand from the major road. Directional median through vehicles. openings are desirable where an intersection is going to be signalized, given that these openings only affect major-road traffic in one direction and that effective two-direction signal Directional Median Opening for Left Turns coordination can be maintained (NCHRP Report 348). This from Major Road at Four-Leg Intersection median opening design is represented in the classification as A directional median opening at a four-leg intersection per- Type 6a--Directional Median Opening for Left Turns mits vehicles to turn left off the major road onto the minor from Major Road at Four-Leg Intersection. road and to make U-turn maneuvers on the major road, but does not permit vehicles to turn left from the minor road onto Figure 33 illustrates this median opening design and its advan- the major road. Median openings at four-leg intersections are tages and disadvantages. appropriate along arterial roadways at street intersections or driveways to major developments where providing access across the median will not create undesirable safety or traffic Midblock Jughandles for U-Turn Maneuvers operational effects. Directional median openings are appro- priate where U-turn or left-turn volumes are relatively high, A midblock jughandle is an indirect left-turn treatment that such that a conventional median opening would experience provides midblock access for vehicles to make a U-turn and

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41 Type 3a--Conventional Median Opening Without Left-Turn Lanes at Three-Leg Intersection Advantages Vehicles on the minor road can make both left and right turns onto the major road. Vehicles on the major road can make left and right turns onto the minor road and make U-turns on the major road. Delays will be less than at a four-leg intersection. No additional VMT is incurred by vehicles making left-, right-, or U-turning maneuvers. Since vehicles making a U-turn only need to enter, but not cross, the opposing roadway, a minimum gap of only 4 to 6 sec will be needed. There are only 11 conflict points, which is less than at a four-leg intersection. Accident rates at three-leg intersections are lower than at four-leg intersections. Disadvantages The absence of left-turn lanes increases potential for rear-end collisions between left-turn or U-turn vehicles and following through vehicles. U-turn vehicles forced to stop in the median opening may encroach on adjacent lanes and interfere with through traffic. U-turn vehicles entering the through lanes may delay full-speed through traffic. Narrow medians may not provide enough space for larger vehicles to negotiate a U-turn. With no directional island, opposing U-turn vehicles may have to overlap. Minimum 6- to 8-sec gaps are needed to cross traffic, possibly even 10 sec where six-lane or eight-lane arterials must be crossed. These gaps will be limited during busy travel period on heavily used arterials. Where peak-hour traffic exceeds critical volumes, vehicles entering the major road from the minor road may experience long delays. Figure 25. Advantages and disadvantages of median opening type 3a--conventional median opening without left-turn lanes at three-leg intersection. reach driveways on the opposite side of the street. Median Type 7b--Midblock Jughandle to the Right for U-turn openings at midblock locations are appropriate on arterials Maneuvers. where providing for U-turn maneuvers between intersections may improve operations at intersections by reducing the U-turn volumes at those intersections or reducing the amount In Type 7a, the U-turning vehicle begins on the inner lane of out-of-direction travel for vehicles trying to reach a desti- of the divided highway, crosses the through-traffic lanes, nation without direct left-turn access. Jughandles are appro- loops around to the left, and then merges with the traffic. To priate with narrow medians, where the provision of a U-turn deter vehicles from stopping on through lanes, a left-turn lane maneuver within the roadway cross section is not possible. with proper storage capacity should be provided to accom- Two types of midblock jughandles have been included in modate turning vehicles. In Type 7b, the U-turning vehicle the classification: exits the major road from the outer lane, loops around to the left, stops clear of the divided highway until a suitable gap in Type 7a--Midblock Jughandle to the Left for U-turn the traffic stream develops, and then makes a normal left turn Maneuvers; and onto the divided highway.