4.2.2 Median Width and Crossover Spacing Similar to the MUT intersection, the median width is a crucial design element for a RCUT intersection. The desirable right-of-way widths needed to accommodate large trucks without allowing vehicles to encroach on curbs or shoulders, assuming 12-ft-wide lanes and 10 ft of shoulder, range from approximately 140 ft for four-lane arterials to approximately 165 ft for eight-lane arterials. For this same situation, desirable minimum median widths between 47 and 71 ft are typically needed. Chapter 3 discussed this in detail and provided the table from the AASHTO Green Book from which designers can obtain minimum median widths based on the needs of different design vehicles executing a left turn. (7) Chapter 3 also discussed several ways in which highway designers can use the MUT intersection concept without requiring the large right-of-ways continuously through the whole corridor. Much of the discussion of crossover spacing provided in chapter 3 for MUTs applies to RCUT intersections. The main points of the discussion included the following: The first method of reducing right-of-way needs is to provide some median openings that only accommodate smaller vehicles. Proper highway signs need to be placed in appropriate locations to prohibit trucks at these crossovers. A second method of reducing the amount of needed right-of-way is to allow vehicles to turn onto a shoulder, which has been strengthened with full-depth pavement. A third way to reduce right-of-way is to provide bulb-outs or loons at the U-turn crossovers. A loon is an expanded paved apron opposite a median crossover. The purpose is to provide additional space to facilitate the larger turning path of a commercial vehicle along narrow medians. (33) Chapter 3 provided discussion on loon design. A fourth method to reduce right-of-way width throughout a RCUT intersection corridor is to use reverse curves on the main street through roadways to widen the median for a short distance at a crossover and then narrow it back down beyond the crossover. Drivers may not initially expect these alignment changes but could quickly adapt to the design. Using any of these methods means that medians do not have to be wider than 16 ft, which accommodates a minimum 4-ft-wide median and a 12-ft-wide turn bay along much of the length of a RCUT intersection design. For these cases, the overall right-of-way required for a corridor of RCUT intersections can be as narrow as 84 ft for four-lane arterials and as wide as 132 ft for eight-lane arterials.
Posted on: Thu, 12 Sep 2013 05:04:33 +0000
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