|
Items in cart [1] |
Questions? Call 888-624-8373 |
| Copyright © 2009. National Academy of Sciences. All rights reserved. Terms of Use and Privacy Statement |
Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter.
Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.
OCR for page 3
3
Chapter One
INTRODUCTION AND OVERVIEW
January 1993, He University of Idaho, in cooperation
with Kittelson and Associates, Ruhr University, and
Queensland Un~versi~ of Technology, inflated work on
a project to develop new capacity and level of service
analysis procedures for unsignalized intersections. This
project, funded through He National Cooperative
Highway Research Program (NCHRP) and designated
project 346, is one of several research projects idendhed
by the Transportation Research Board's (TRB)
Committee on Highway Capacity and Qualm of Service
(Committee A3AlO) needed to improve He capacity and
level of service analysis techniques available to practicing
traffic eng nears. It Restart of an effort by the Committee
to develop a new version of He Highway Capacity
Manual (HCM) by He year 2000.
While most over chapters of He 1985 HCM are
support by one or more nationally funded research
projects, Chapter Ten borrows heavily from a procedure
for two-way stop-controlled (TWSC) intersections
originally developed in Germany. Unfortunately, He
procedure was backed by only limited calibration data
reflecting conditions found in He United States. For all-
way sto~con~olled (AWSC) intersections, Chapter Ten
Included only capacity guidelines wad no level of service
methodology. The recently released 1994 HCM Update
remedies some of He deficiencies. A new delay equation
for TWSC intersections is introduced and a completely
new procedure for capacity and level of service analysis
for AWSC ~ntersecdons is added. Deficiencies still
remam, however. The TWSC intersection procedures
have not been calibrated wad a data base reflecting U.S.
driving conditions, He analytical procedure for TWSC
intersections cannot account for platooned flow on He
major sheet, He methodology fails to provide guidance
regarding He use of signalized vs stop-sign control at a
given ~ntersecdon, and He data base for AWSC
ntersecdons is sdD limited.
NCHRP 346 win produce a new version of Chapter Ten
of the HCM as well as a new version of He supporting
Highway Capacity Software (HCS) Hat will address
these deficiencies. The computational procedures
included in bow products are based on He first-ever
comprehensive data base for traffic flow characteristics
at un ign~li~d interaction in He United Sates, including
information from 79 TWSC and 41 AWSC intersections.
Each site was videotaped for a period of between one and
two hours. The final procedures were selected from an
evaluation of sixteen candidate models for forecasting
capacity and delay at unsignalized intersections.
The research complete as part of NCHRP 346 has lead
to nine recommendadons from He project Ram, all now
approved by the pane} overseeing this project.
For TWSC intersections:
.
.
.
.
.
.
.
The Harders gap acceptance mode! should be
used as He basis to compute the capacity of a
non-priority traffic stream at a TWSC
intersection.
New weighing factors for computing the
effective conflicting steam flow rate have been
identified and documented and should replace
those now used in the 1994 HCM Update.
New values for the critical gap and follow-up
time for each non-priority traffic stream based
on geometry conditions and traffic stream
composition have been documented and should
replace those now used in the 1994 HCM
Update.
The basic procedure used In the 1994 HCM
Update to compute stream capacity should be
continued including adjustments to account for
impedance and shared lanes.
Adjusunen~ to capacity estimates to account for
upstream signals should be made if the signal is
less than 1200 feet from the intersection.
The 1994 HCM Update delay equation should be
used to forecast delay.
An extension of the current project should be
approved for the development of a simulation
mode} for TWSC intersections. Existing
simulation models do not yield satisfactory
results and/or are not comprehensive enough to
account for general U.S. conditions.
OCR for page 4
4
For AWSC Intersections:
The service time model, an extension of
Richardson's model, should be used as the basis
to forecast departure headways. A set of
saturation headways is recommended as input to
this model.
The Troutbeck equation should be used to
forecast delay.
This report is the second of two volumes documenting Be
work completed for NCHRP 346. Volume one
describes the work completed for two-way stop-
controlled intersections.
Volume two Includes eight chapters documenting Me
work completed for all-way stop-controlled intersections.
Chapter two describes previous research work or studies
that have been completed for AWSC intersections.
Chapter three lists He candidate models for capacity and
delay Hat were considered. Chapter four describes the
field data collection effort that produced the data base
used in the mode} testing and validation. Chapter five
describes the analysis of saturation headways. Chapter
six describes the concepts of service time and capacity
and He validation of the service time model. Chapter
seven describes the validation of the delay model.
Chapter eight documents He computational procedures
that will be recommended for inclusion in the HCM.
Representative terms from entire chapter:
service time
