|
Items in cart [0] |
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
Chapter One
INTRODUCTION AND OVERVIEW
~ January 1993, the University of Idaho, In cooperation
with Kittelson ~ Associates, ~c., Rubr Ur~versi~, and
Queensland Untversibr of Technology, initiated work on a
project to develop new capacity and level of senice
analysis procedures for unsignalized intersections. This
project, funded through the National Cooperative Highway
Research Program (NCHRP) and designated project 3-46,
was one of several research projects identified by the
Transportation Research Board's Committee on Highway
Capacity and Quality of Service (Committee A3AlO)
needed to improve the capacity and level of service
analysis techniques available to practicing traffic
engineers. It is part of an effort by the Committee to
develop a new version of the Highway Capacity Manual
(HCM) by the year 2900.
While most other chapters of He 1985 HCM were
supported by one or more nationally funded research
projects, Chapter Ten borrowed heavily from a procedure
for two-way stop-controlled (TWSC) intersections
originally developed in Germany. Unfortunately, the
procedure was backed by only I~m~ted calibration data
reflecting conditions found in the United States. For ad-
way stop-controDed (AWSC) intersections, Chapter Ten
included only capacity guidelines with no level of service
methodology. The recently released 1994 HCM Update
remedied some of the deficiencies. A new delay equation
for TWSC intersections was introduced and a completely
new procedure for capacity and level of service analysis for
AWSC intersections was added. Deficiencies still
remained, however. The TWSC intersection procedures
had not been calibrated with a data base reflecting U.S.
driving conditions, the analytical procedure for TWSC
intersections could not account for platooned flow on the
major sweet, the methodology failed to provide guidance
regarding the use of signalized vs. stop-sign control at a
given intersection, and the data base for AWSC
intersections was still vomited.
NCHRP 3-46 watt produce a new version of Chapter Ten
of the HEM as well as a new version of the supporting
Highway Capacity Software (TICS) to address these
deficiencies. The computational procedures included in
both products were based on the first-ever comprehensive
data base for traffic flow characteristics at unsignalized
1:
ntersections in the United States, including information
from 79 TWSC and41 AWSC Intersections. Each site
was videotaped for a period ofbetween 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 completed as part of NCHRP 3-46 lead to
nine recommendations from the project team, 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 capacitor of a non-
priority traffic stream at a TWSC intersection.
New weight factors for computing the effective
conflicting stream flow rate have been identified
and documented and should replace those now
used In the 1994 HCM Update.
New values for He critical gap and follow-up time
for each nompriority traffic stream based on
geometry conditions and traffic steam
composition have been documented and should
replace those now used in He 1994 HCM Update.
The basic procedure used in the 1994 HCM
Update to compute stream capacity should be
continued including adjus~nents to account for
impedance and shared lanes.
Adjustments to capacity estimates to account for
upstream signals should be made if a signal is less
than 1,200 feet (400 m) Tom He intersections.
The 1994 HCM Update delay equation Known as
Troutbeck's equation) should be used to forecast
delay.
There is a need for the development of better
simulation models for TWSC intersections.
Existing simulation models Hat were tested do
not yield satisfactory results and/or are not
comprehensive enough to account for general U.S.
conditions.
For AWSC Intersections:
· The service time model, an extension of
OCR for page 4
4
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 1994 HEM Update delay equation should be
used to forecast delay.
This report is the first of two volumes documenting the
work complete for NCHRP 3-46. Volume two descnbes
the work completed for all-way stop-controlled
intersections. Volume one include ten chapters
documenting the work completed for two-way stop-
controlled intersections. Chapter two describes the
theoretical background of previous research work or
studies Hat have been completed for TWSC intersections.
Chapter Free lists the candidate models for critical gap
and follow-up time estimation as well as for capacity and
delay. 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
critical gap and fodow-up times. Chapter six describes He
capacity mode! testing process and results. Chapter seven
describes delay mode! testing process and results. Chapter
eight documents He special conditions while analyzing
TWSC intersections. Chapter nine discusses issues of
signal warrants and level-of-service concept. Chapter ten
provides He recommended computational procedures.
Representative terms from entire chapter:
hcm update
