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SUMMARY
In January 1993, Be University of Idaho, in cooperation
with Kittelson and Associates, Ruhr University, and
Queensland University of Technology, initiated work on
NCHRP 346 to develop new capacity and level of
service analysis procedures for unsignalized intersections.
This report is Me second of two volumes documenting He
work completed for this project. Volume one describes
the work completed for two-way stop-con~olled
intersections. Volume two includes eight chapters
documenting He work completed for as-way stop-
con~olled (AWSC) intersections.
A new data base describing traffic operations at AWSC
~ntersecdons was assembled as part of this study. Thirty
unique sites were videotaped during 41 different time
penods. In most cases, four video cameras were used at
each site producing over 150 individual videotapes. A
total of 151.67 hours of usable data was acquired.
Field observations chow Hat AWSC intersections operate
in either two-phase or four-phase patterns, based
primarily on He complexion of the intersection geometry.
Flows are determined by a consensus of right of way that
alternates between the north-south and east-west steams
(for a s~ngle-lane approach) or proceeds in turn to each
intersection approach (for a multi-lane approach
intersection).
The basic parameter used to compute intersection capacity
is saturation headway. Based on data from over 22,000
vehicle records, it was found dlat He saturation headway
is dependent on (~) He degree of conflict faced by the
subject driver as measured by He presence of vehicles on
the opposing and conflicting approaches, (2) the
~ntersechon geometry, particularly He number of lanes on
He conflicting approaches, He opposing approach, and He
subject approach, (3) the directional movements of the
interacting vehicles, and (4) the vehicle type.
New models for estimating saturation headway, service
~me, capacity, and delay are recommended. The models
were subject to a series of validation tests using the data
collected as part of this study. Level of service forecasts
produced by He new set of models are of better quality
than those produced by He existing 1994 HCM Update
procedure. ~ addidon, the severe range restrictions now
a part of He 1994 procedures will no longer apply Bus
giving He practicing traffic engineer He capability to
produce good quality forecasts for a much wider range of
traffic conditions Man is possible today.
. . ,
OCR for page 2
Representative terms from entire chapter:
conflicting approaches
