Safe and Aesthetic Design of Urban Roadside Treatments (2008) / Chapter Skim
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Pages 37-49
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From page 37... ...
includes a toolbox that generally summarizes the safe application of roadside elements in an urban environment. A supplemental product of this research effort is draft language for possible inclusion in the urban roadside chapter of the AASHTO Roadside Design Guide.
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From page 38... ...
These zones are summarized in the sections that follow. Findings and Recommendations The various corridors the research team evaluated for identification of potential urban control zones included a wide variety of speed limits, physical features, and types of crashes.
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R oa ds id e di tc h w ith n on tr av er sa bl e he ad w al ls U ne v en r o ad sid e w ith o bs ta cl es (o ffs et va rie s) C o rr id or c le ar z on e no t m ai nt ai ne d at ri gh t -t ur n la ne s G ua rd ra il w ra pp ed a ro un d c u rb re tu rn L o ng itu di na l b ar rie r/g ua rd ra il o ffs et 2 –6 ft S c en ic / to ur ist lo ca tio n w ith c l os e ob sta cl es UCZ-CA-1 SH 1, Orange County, CA x x x x UCZ-CA-2 SH 39, Orange County, CA x x UCZ-CA-3 SH 74, Orange County, CA x x UCZ-CA-4 SH 75, San Diego County, CA x x x x UCZ-CA-5 SH 76, San Diego County, CA x x UCZ-CA-6 SH 78, San Diego County, CA x x x UCZ-CA-7 SH 90, Orange County, CA x x x UCZ-GA-1 Alpharetta Highway, Fulton County, GA x UCZ-GA-2 Briarcliff Rd., DeKalb County, GA x x x x UCZ-GA-3 Candler Rd., DeKalb County, GA x x x UCZ-GA-4 14th St./Peachtree St., Fulton County, GA x x UCZ-GA-5 Franklin Rd., Cobb County, GA x x UCZ-GA-6 Moreland Dr., DeKalb County, GA x x x UCZ-GA-7 Roswell Rd.
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From page 40... ...
This operational offset was never intended to represent an acceptable safety design standard, although it was sometimes misinterpreted as being one. The urban environment limits lateral offset distances simply because of the restricted right-of-way widths common to an urban setting.
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From page 41... ...
Evaluation of the role of trees in crashes was difficult because the types of trees in the selected study corridors varied dramatically and included mature rigid trees as well as small-caliper ornamental trees. Due to the varying nature of the tree placement along the corridors (and the wide range of their frangible tendencies)
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From page 42... ...
This suggests that the lateral offset placement of objects at horizontal curves should be increased wherever possible. Roadside Objects Placed Near Lane Merge Points The placement of roadside objects in the vicinity of lane merge points increases the likelihood of vehicle impact with these objects.
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From page 43... ...
This does not, however, modify the recommended minimum lateral offset from the curb face. Objects Placed Inappropriately in the Sidewalk Buffer Treatment The placement of roadside objects immediately adjacent to active travel lanes at some corridor sites increased when a sidewalk was physically separated from the curb by a 43 Speed Limit km/h (mph)
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From page 44... ...
At several sites, however, the research team observed smaller, more forgiving objects, such as landscaping with smallcaliper trees, positioned near the center of the buffer strip and the more rigid poles and light standards positioned immediately adjacent to the sidewalk and as far from the active travel lane as possible. The crash analysis at these staggered-object-placement buffer strips showed very few roadside crashes.
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From page 45... ...
6" Buffer Strip Width > 4' A dja cen t L an e Landscape and Rigid Object Placement for Buffer Strip Widths > 4' Curb Face Rigid Objects Placed on Far Side of Sidewalk Si de w al k Frangible Objects Only in Buffer Strip Region Curb Width Approx. 6" A dja cen t L an e Buffer Strip Width < 4' Landscape and Rigid Object Placement for Buffer Strip Widths ≤ 4' Figure 19.
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From page 46... ...
At these locations, roadside objects were hit more frequently even when lateral offsets to the objects were similar to those at other crash-free sites. Regardless of the cause, additional lateral offset to objects in these or similar locations seems prudent to minimize the risk of hazardous run-off-road crashes for unfamiliar drivers.
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From page 47... ...
Often before-after analyses are limited because researchers study corridors where safety issues are prominent and so the resulting improvements can be dramatic; however, for the beautification and roadside enhancement projects the focus is not on operations and safety but rather on aesthetics and livability. As a result, the before-after analysis can provide a useful indication about possible safety implications of a change to the road environment.
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From page 48... ...
Only three of the case study sites exhibited an increase greater than one additional severe crash per year. All three of these case study sites included sidewalk improvements with buffer strips, but several similar improvement projects resulted in little change to a reduction in severe crashes.
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From page 49... ...
General Recommendations The use of corridor video analysis combined with historic crash statistics provided meaningful insight into urban roadside crash conditions and locations where roadside objects should not be located, if possible. Conversely, the use of roadside improvement or beautification case studies did not directly help to address specific roadside safety issues, but these case studies can be used by an agency proposing similar projects to determine expected overall safety performance of these improvements.
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