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50 CHAPTER 4 Conclusions and Suggested Research Conclusions Each of these urban control zones is reviewed in detail in Chapter 3. The recommendations that are the result of this The urban roadside environment is complex. Due to the research effort are the following: constrained nature of this built environment, it is difficult for a designer to achieve an acceptable clear zone, free of objects. Where possible at curb locations, provide a lateral offset to As a result, a lateral offset that enhances roadway operations rigid objects of at least 1.8 m (6 ft) from the face of the curb may be used, but this offset does not represent a safe place- and maintain a minimum lateral offset of 1.2 m (4 ft). ment for rigid roadside objects. At lane merge locations, do not place rigid objects in an area This research identified known safety characteristics that is 3.0 m (10 ft) longitudinally from the taper point. This and placement strategies for urban roadside objects by will result in a 6.1-m (20-ft), object-free length at the taper means of a comprehensive literature review. Following point. The lateral offset for this 6.1-m (20-ft) section should this state-of-the-practice identification, the research team be consistent with the lane width, typically 3.7 m (12 ft). further evaluated roadside safety conditions using two Although many auxiliary lanes, such as bus lanes or bicy- approaches. cle lanes, have low volumes and may be included as part of First, the research team videotaped over 241 km (150 mi) a clear zone in the urban environment, higher speed aux- of urban corridors and compared their 6-year crash history iliary lane locations, such as extended length right-turn and crash locations to the various roadside features observed lanes, are common locations for run-off-road crashes. on these corridors. The result of this assessment was the iden- A lateral offset of 1.8 m (6 ft) from the curb face to rigid ob- tification of several potential urban control zones. These jects is preferred, and 1.2-m (4-ft) minimum lateral offset locations are shown to have a greater likelihood of crashes should be maintained. and, as a result, should be kept free of rigid objects whenever At locations where a sidewalk buffer is present, rigid ob- possible. These urban control zones include locations with jects should not be located in the buffer area when it has the following: a width of 0.9 m (3 ft) or less. For buffer widths greater than 0.9 m (3 ft), lateral offsets from the curb face to rigid Obstacles in close lateral proximity to the curb face or lane objects should be maintained with a minimum offset of edge; 1.2 m (4 ft). At these wider buffer locations, other frangi- Roadside objects placed near lane merge points; ble objects can be strategically located to help shield any Lateral offsets not appropriately adjusted for auxiliary lane rigid objects. treatments; Rigid objects should not be located in the proximity of Objects placed inappropriately in sidewalk buffer treatments; driveways, and care should be taken to avoid placing rigid Driveways that interrupt positive guidance and have ob- objects on the immediate far side of a driveway. In addi- jects placed near them; tion, objects should not be located within the required Three kinds of fixed-object placement at intersections; sight triangle for a driveway. Unique roadside configurations associated with high crash occurrence; and A second component of this research included a case study Roadside configurations commonly known to be hazardous. assessment for roadside enhancement or beautification