Our Extensive Project Experience
Summary of Akcelik & Associates Project Experience
Research, development and consultancy projects
undertaken by Akcelik & Associates since 1999 (other than software development
projects) include the following. Various articles and reports based on
these projects are available from our
Downloads page.
- Performance of Roundabouts With Metering Signals (major research project for
VicRoads).
- Investigation of Alternative Models for Roundabout Capacity Estimation.
- Speed-Flow and Bunching Models for Uninterrupted Flows.
- Revision of AUSTROADS Guide to Traffic Engineering Practice Part 6 - Section 3
(Performance of Roundabouts).
- Revision of AUSTROADS Guide to Traffic Engineering Part 7 (Signals)
- Published June 2003.
- Review of SIDRA INTERSECTION analyses for a sign-controlled intersection.
- An Investigation of Potential Greenhouse Gas Emission Reductions from Various
Traffic Management Measures.
- Pedestrian Movement Characteristics at Signalised Crossings.
- HCM 2000 Back of Queue Model for Signalised Intersections.
- Progression Factors in the HCM 2000 Queue and Delay Models for Traffic Signals.
- Analyses of Roundabouts with Metering Signals Using SIDRA INTERSECTION.
- Evaluation of Roundabout Design.
- Review of Traffic Operation Analysis for Charing Cross Intersection, Bendigo
- Modelling Vehicle Paths Through Roundabouts
- Acceleration and Deceleration Characteristics of Vehicles at Intersections.
- Relating Microsimulation and Analytical Models.
Microsimulation Models
The ever-increasing power of personal computers and search for Intelligent
Transport Systems (ITS) solutions to growing urban transport problems has led to
the emergence of a number of microscopic simulation models as practical traffic
analysis tools. There is great potential for useful application of
microsimulation models to the analysis of complex traffic problems in urban
areas, alongside the analytical techniques that are in use. However, concerns
are often expressed regarding misuse of microsimulation.
Compatibility between microsimulation methods and established analytical
techniques that are used in traffic engineering is an area of interest to
Akcelik & Associates. Comparison of specific microsimulation and analytical
model components has been recommended towards model benchmarking for evaluation
of new and existing models.
Signalised Intersection Guides
ARRB Research Report ARR No. 123 by R. Akçelik was published in 1981 to replace
Bulletin No. 4 as the Australian signalised intersection capacity guide. Since
then minor revisions of ARR 123 were undertaken, and five reprints of the guide
were published (latest in 1995). This publication is referred to extensively in
the traffic analysis literature.
A major revision of the AUSTROADS Guide to Traffic Engineering Part 7 (Traffic
Signals) was undertaken by AUSTROADS. R. Akçelik acted as the technical editor
and writer to implement this revision under the directions of an AUSTROADS
reference group. This Third Edition of the Traffic Signals Guide was published
in June 2003.
R. Akçelik has made numerous contributions to the US Highway Capacity Manual,
including the back of queue model and actuated signal analysis method for the
Signalised Intersections chapter, as well as contributions to the Interchange
chapter of the Manual.
Roundabouts and Sign-Controlled intersections
The roundabout modelling method described in ARRB Special Report SR 45 was
introduced into SIDRA in 1991 with some variations and extensions. The method
was also incorporated into the Australian roundabout design guide, AUSTROADS
Traffic Engineering Practice, Part 6 (1993) with some minor modifications.
Fundamental work on arrival headway distributions was carried out, and new
capacity and performance models were developed for roundabouts and other
unsignalised (sign-controlled) intersections. Following further research and
development, significant enhancements were introduced in 1995, particularly the
effects of arrival flow O-D patterns and queuing at roundabout approach roads
were included in capacity estimation. Further enhancements were introduced in
later versions of SIDRA. The method was described in detail in the Research
Report ARR 321. Research on roundabouts with part-time metering signals was
conducted under funding by Vic Roads, and is continuing under Akcelik &
Associates. New methods for modelling vehicle paths through roundabouts has been
undertaken by Akcelik & Associates and was implemented in aaSIDRA 2.
A revision of AUSTROADS Guide to Traffic Engineering Practice Part 6 - Section 3
(Performance of Roundabouts) was undertaken for AUSTROADS. The revision
aimed to achieve consistency between the methods used in the AUSTROADS Guide and
the SIDRA INTERSECTION software.
Performance of Roundabouts With Metering Signals
A major project was undertaken for VicRoads to investigate the performance of
roundabouts with metering signals in Melbourne, Australia. The research
objectives included further development of analytical techniques to assess the
performance of roundabouts with metering signals, and calibration and validation
of these techniques for incorporation into the SIDRA Intersection software.
Twenty roundabouts with metering signals were identified in the project brief.
Following site visits, a total of five multi-lane roundabout sites were chosen
for comprehensive surveys of traffic and driver behaviour at roundabouts with
metering signals. The survey data included video recordings of driver gap
acceptance behaviour, turning movement volumes, automated counting of
circulating traffic, GPS-equipped floating car surveys, and signal timing. Using
the survey data, the circulating and entering traffic characteristics were
investigated at the controlling and metered roundabout approaches. These
included critical gap and follow-up headways of vehicles in entry lanes,
proportion of free (unbunched) vehicles and speeds in circulating traffic, and
queue lengths, delays and average queue spacings for traffic queued in entry
lanes. This paper presents various aspects of data collection, analysis, and
findings of the project.
Intersection Design Software development
Staged development of the SIDRA INTERSECTION software to incorporate
latest research results and to keep the software up to date for features
compatible with modern operating systems, and user support and training
activities as a technology transfer tool, have been undertaken by Akcelik &
Associates over many years.
Original version SIDRA-1 was developed by Dr Akçelik during 1975-1979. SIDRA 2
based on ARRB Research Report ARR 123 was developed and first released as a
main-frame computer program in 1984. Further development, distribution and
support of SIDRA was undertaken, including workshops and training courses. The
U.S. Highway Capacity Manual methods for capacity analysis were reviewed and
some features adopted into SIDRA. A survey of research needs in the user
community was undertaken. The results of external research to update the
Australian saturation flow database were adopted. Documentation on the advanced
methods incorporated into SIDRA was prepared (ARRB TR Research Reports ARR 180
and ARR 321, and the SIDRA User Guide). The last version developed under ARRB
Transport Research Ltd, SIDRA 5.2 was released in 1999.
Full ownership of SIDRA was transferred to Akcelik & Associates Pty Ltd on 22
February 2000. Akcelik & Associates released aaSIDRA 1.0 in July 2000. The
latest major version
Akcelik & Associates acquired the ownership of SIDRA software in February 2000.
SIDRA was renamed aaSIDRA©, short for Akcelik & Associates SIDRA. First major
new version by Akcelik & Associates (aaSIDRA 1.0) was released in July 2000,
followed by major versions 2.0 and 2.1 during released during the following
years. In 2006, Akcelik & Associates Pty Ltd introduced SIDRA SOLUTIONS©
as the brand name for its software products. SIDRA INTERSECTION version 3.0 was
released in July 2006 as a software product developed in full Windows
environment (the product name SIDRA INTERSECTION was introduced to replace
aaSIDRA). A new major version version 3.2 is expected to be released
during 2007.
Fundamental Characteristics of Traffic at Signalised Intersections
The initial objective was to develop analytical models for traffic operations at
closely-spaced (paired) intersections. This involved modelling of queue
interaction (relationships between the upstream saturation flow and downstream
queues) and platooned arrivals. The platooned arrival models are described in
ARRB TR Research Report ARR 276, and have been implemented in SIDRA.
Field surveys were carried out to establish fundamental traffic relationships at
the signal stop line. The latest stage of this research was funded by the Roads
and Traffic Authority of New South Wales. The results of this research are
described in ARRB Research Report ARR 340. The report presents findings of a
study of fundamental traffic characteristics at signalised intersections based
on surveys of queue discharge headways and speeds for individual vehicles and
jam spacings at eighteen intersections in Sydney and Melbourne. Exponential
queue discharge flow, headway and speed models are given. Other traffic
parameters considered are spacing, gap length, density, gap time, occupancy
time, space time, occupancy ratios, queue clearance wave speed, departure
response time, saturation flow rate, start loss and end gain times. The report
presents basic material on fundamental traffic flow relationships, describes the
survey methodology, survey site characteristics, data processing, analysis
method, calibration method, and presents calibration results. Results on
uninterrupted flow models and downstream queue interference at paired
intersections are presented. Implications of findings on capacity and
performance modelling and adaptive signal control practice are discussed.
Relationships for use in practice are given.
Work to help determine acceleration characteristics from other queue discharge
parameters was carried out under Akçelik & Associates.
Vehicle Actuated Signals and SCATS Master Isolated Control
The vehicle-actuated signals project developed analytical models for estimating
average green and cycle times for use in capacity and performance estimation
(delay, queue length, stop rate, etc) at intersections controlled by various
types of vehicle-actuated signals (gap control only, gap and waste control. The
work involved consultancy for the US project NCHRP 3-48 (Principal Investigator:
Prof. Ken Courage, University of Florida), development of methods considering
the Australian vehicle-actuated signal control practices, evaluation of the
SCATS Master Isolated control method, and improved control algorithms for SCATS
II. The actuated signal timing prediction model developed by Akçelik was
incorporated into the Highway Capacity Manual 1997 edition, and the queue model
was incorporated into the HCM 2000.
Various projects for the Roads and Traffic Authority of New South Wales
developed various SCATS-like control algorithms and tested them through
extensive MODELC simulation tests for constant and variable demand conditions
with a wide range of demand flow levels. Algorithms for both isolated and
coordinated signals were investigated. The traditional vehicle-actuated and
fixed-time control were also evaluated. An evaluation of detector failure cases
was also undertaken.
Freeway Traffic Flow Models
A study of fundamental characteristics of freeway traffic flows was carried out
under AUSTROADS funding. The results of this research are described in ARRB
Research Report ARR 341. The findings of the report are based on analysis of
individual vehicle data collected on the Eastern Freeway in Melbourne under both
saturated and unsaturated conditions using a two-loop presence detection system.
The aim of the study was to assess data collection and analysis methods, and to
develop analytical models to describe the relationships between traffic flow
parameters. The traffic flow parameters considered included flow rate, speed,
density, spacing, gap length, vehicle length, headway, occupancy and space time,
gap time, vehicle passage time and occupancy ratios. Travel speeds were also
measured using an instrumented car. Six analytical traffic flow models were
presented including various single-regime and two-regime models.
Fuel Consumption, Emission and Acceleration-Deceleration Models
ARRB Research Report ARR No. 124 and Special Report No. 32 presented the results
of extensive research work on fuel consumption modelling. Improved models
of acceleration and deceleration of vehicles in urban traffic were developed.
A revision of acceleration and deceleration models was undertaken by Akcelik &
Associates. The results of this work have been adopted into SIDRA
INTERSECTION and SIDRA TRIP software packages.
People and Goods Models
A preliminary assessment of the use of people and goods models in lieu of
vehicle models in traffic management was carried out under AUSTROADS funding.
The purpose was to provide a clear understanding of the practicality of
developing design and evaluation tools for traffic management practice
considering people and goods rather than vehicles, to review models and
modelling needs; carry out literature review as to current availability of
relevant models and methods.
Traffic Frustration Index
Driver comfort, frustration and stress are all relevant issues in the discussion
of quality of travel. A study was undertaken under AUSTROADS funding to
investigate which parameters of traffic flow actually relate to driver annoyance
or dissatisfaction, and to find some way of combining these factors in order to
give each a weighting that reflects the extent to which they relate to annoyance
and dissatisfaction. A laboratory experiment was conducted based on a simulated
drive to determine how drivers react to potentially frustrating situations, a
traffic flow index (TFI) was developed from these experimental results and
validated against ratings of traffic conditions obtained from road users
familiar with the roads to which the TFI was applied. The results of the
research are presented in the AUSTROADS Report AP-R160/00 "Traffic Management
Performance - Development of a Traffic Frustration Index" (free download is
available from AUSTROADS).
Software Integration
ATSIS (Australian Transport Software Integration System) was developed as a
flexible data language to link transport software packages for the design,
planning and evaluation of urban traffic facilities. ARRB TR Research Report ARR
345 describes the general features of the ATSIS format, including basic concepts
of the file structure, data hierarchy and level of detail in data provision.
Various aspects of the ATSIS method were used in SIDRA INTERSECTION.
Other research and development projects undertaken by R. Akçelik
Analysis of Signal Coordination and Bus Priority Measures for City North Area.
National Capital Development Commission, Canberra, 1977-78.
Evaluation of Area Traffic Control Measures for the City Centre. National
Capital Development Commission, Canberra, 1976-1977.
TRANSYT Version 6N for Traffic Signal Network Optimisation and Simulation.
National Capital Development Commission, Canberra, 1977-78.
Application of Australian Traffic Engineering Techniques to Signalised
Intersection Operations in Turkey. A six-week United Nations Development
Programme TOKTEN Project at Istanbul Technical University, 1991, Istanbul,
Turkey
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