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projects. At these locations, the governing agencies incor- A third issue for future research is the definition of a haz-
porated a variety of urban roadside changes to improve the ardous tree. Although this study identified some recommended
aesthetic quality of the roadside and enhance the functional tree placement strategies, the concept of a tree as a rigid object
use of the space, often with particular emphasis on pedes- requires further definition. Historically, a tree with a caliper
trian facilities. Although the findings of this task were in- width of 4 in. or more has been considered a rigid object, but
conclusive, the individual case studies can be used by agencies the literature review indicated that this dimension was based
to help determine general safety trends for similar future on wooden pole crash tests. The influence of tree type (soft
projects. wood versus hard wood), tree size, root system configuration,
and similar issues merits further consideration.
A fourth issue for further research resulting from this eval-
Suggested Research
uation is the influence of moving light standards farther from
This research effort creates a foundation for better under- the travel lane and how this change in location might affect
standing on how urban roadside configurations can influence nighttime visibility. At the study corridors, numerous light
safety. As with any such effort, the questions answered by this standards located close to the road were hit by vehicles, so
research also help to identify knowledge gaps. The gaps could the recommendation to move these lights closer to the near
substantially benefit from future research efforts. side of the sidewalk or even to the far side of the sidewalk
Specifically, the research team identified five specific issues would probably improve safety as it relates to roadside haz-
that merit additional research. The first issue is the influence ards. The effect of this relocation of the street lights on safety
of positive guidance at driveway and intersection locations. as it relates to visibility merits further evaluation for light
This issue appeared to contribute to crash conditions; how- pedestals that do not include mast arm configurations that
ever, the disproportionate number of sites where positive can be easily lengthened.
guidance in the form of a white edge line was not present pro- The fifth issue for further research is roadside improvements
hibited the researchers from drawing definitive conclusions at intersections where pedestrian access ramps appear to direct
regarding this issue. an errant motor vehicle toward a rigid object (often a signal
The second issue of interest is the evaluation of auxiliary pole). It seems like a minor issue to shift the pole so that this
lanes and their role in roadside safety. In some instances, the conflict is minimized; however, often a pedestrian button is
inclusion of a bicycle lane provided an additional offset to located on the pole, and this relocation could adversely affect
roadside objects. At these locations, the number of roadside operations for the pedestrian. As a result, the placement of
crashes appeared to be reduced. This observation suggests traffic signal poles in relation to access ramps, roadside safety,
that the bicycle lane can be included as part of the available and pedestrian usability should be assessed.
clear zone and that at locations where this occurs, the white Finally, the research team identified one additional item
stripe that separates the motor vehicle lane from the bicycle that is not included in the five research issues but appears to
lane could serve as the edge of the clear zone. Alternatively, warrant further evaluation. For the corridor analysis task, the
some of the sites studied included what appeared to be an research team attempted to identify corridors with relatively
almost continuous right-turn lane (referred to in the report high operating speeds (as higher speed crashes generally result
as an extended right-turn lane). At these locations, turn in greater injury severity). A few of these corridors transi-
movements were channelized by pavement markings only. tioned into lower speed corridors with on-street parking and
A large number of crashes occurred when these auxiliary turn curb extensions. The curb extensions generally were posi-
lanes functioned similarly to through lanes, yet lateral offsets tioned to help define intersections and to enable shorter
were not increased. At locations where upstream or down- pedestrian crossing distances. Since the number of sites with
stream lateral offsets were approximately 4.3 m (14 ft), these this lower speed configuration was limited, the research team
offsets were reduced to less than 0.6 m (2 ft) adjacent to the could not comprehensively evaluate these curb extension
turn lanes. The number of roadside crashes dramatically in- locations. However, at the few locations where the research
creased as a result. Future research should investigate when team did observe these extensions, roadside crashes appeared
an auxiliary lane should be treated as another motor vehicle to peak during nighttime hours, presumably when on-street
lane. For example, could a short right-turn pocket be treated parking was limited. Due to the small sample size, the re-
like a bicycle lane and this width be included in the clear zone search team could not draw any definitive conclusions; there-
or should any lane designed for motor vehicles, regardless of fore, the team strongly recommends that roadside safety at
its function, be treated similarly? curb extensions be the subject of future research.
