Ordinances-2003-260

1. Channelizing Islands When an exclusive left turn lane is to be used for a driveway, channelizing islands shall be used for delineation. The minimum width of the channelizing island shall be 4 feet. This can be provided within a median 4 to 6 feet wide and a turning lane width of 12 feet. Curb and/or painted channelizing islands may be used subject to the design speed of the highway. 2. Island Nose Offsets For curbed islands 4 feet or more in width, the curbed nose can be offset from the opposing through traffic lane 2 feet or more, with gradual taper beyond to make it less vulnerable to contact by through traffic. The shape of the nose for curbed dividers 4 feet wide should be semicircular, but for wider width the ends are normally shaped to a bullet nose pattern to conform with the paths of turning lanes. 3. Approach and Lane Tapers The tapering of exclusive left turning lanes and the approach tapers for medians shall be in accordance with current Iowa Department of Transportation polices. 4. Storage Capacity The left turn lane should be sufficiently long to store the number of vehicles likely to accumulate during a critical period. The storage length should be liberal to avoid the possibility of left-turning vehicles stopping in the through lanes. The storage length should be sufficiently long so that the entrance to the left lane is not blocked by vehicles standing in the through lanes waiting for a signal change or for a gap in the opposing traffic flow. At unsignalized intersections the storage length, exclusive of taper, may be based on the