Aerial photograph of road


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.


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.


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.


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.


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.


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. 


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.


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.


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.


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.


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.


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).


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.


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.