A
number of urban and suburban cities have inherited arterials that have
been shown to be undesirable, given increases in traffic volume, intensity
of land use and level of pedestrian traffic. These arterials
generally consist of 5 lanes, with the center lane being a two-way left
turn lane (TWLTL).
As
a result of these situations, many cities are proposing streetscape
redevelopment projects, which would convert the existing arterial into
more of a "boulevard-type" street section. These proposed
projects generally include raised medians and median landscaping.
The landscaping proposal is an area that generally conflicts with existing
standards - namely trees vs. clear zone policy.
This
sub-committee's work allows these proposed projects to proceed forward,
using the projects to perform an In-Service Evaluation on several new
urban median design concepts along SR 99, within the cities of SeaTac,
Federal Way, and Des Moines.
Each
In-Service Evaluation consists of at least a 3-year monitoring and data
collection period after installation of the median and trees. Each
proposal also includes a mitigation strategy, should the evaluation
indicate unacceptable results.
The
evaluations are being conducted through a collaborative effort between the
University of Washington's Transportation Center (UW-TRAC); WSDOT
Northwest Region Traffic and Design; WSDOT HQ Design; and the respective
local agency.
The
ideal results of this sub-committee's work will be the development of new
urban arterial median design solutions that preserve roadway safety, while
allowing greater flexibility for also meeting community goals and
objectives.
As
evaluations are completed, they will be posted on this web page.
NEW The following link covers a
report and
folio by Anna St.
Martin on Median Trees.
The following link covers a report by California Poly. State University on
Safety of Median Trees with Narrow Clearances on Urban Conventional
Highways.
http://ceenve.calpoly.edu/sullivan/trees/
Outline of the In-Service Evaluation
process.
- Mark Leth, WSDOT NW Region Traffic (lead)
- Samih Shilbayeh, WSDOT HQ Design
- Mark Bandy, WSDOT NW Region Traffic
- Tom Gut,
City of Sea Tac
- Maiya Andrews, City of Des Moines
- Ken Miller, City of Federal Way
Date of last update:
February 05, 2007
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