Rahmi Akçelik

Rahmi Akçelik
SIDRA SOLUTIONS (Akcelik & Associates Pty Ltd)

PhD

About

147
Publications
113,025
Reads
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2,754
Citations
Introduction
Dr Rahmi Akçelik is a leading scientist and software developer with 50 years of practical, research and training experience in the area of road traffic operations, traffic engineering, management and control. He is Director of the multi-award winning SIDRA SOLUTIONS and author of the SIDRA INTERSECTION and SIDRA TRIP software packages - powerful tools used by traffic engineers and planners in over 2200 organisations across 90 countries, for solving intersection and network traffic problems.
Additional affiliations
July 1979 - July 1999
Independent Researcher
Position
  • Chief Research Scientist
Description
  • Research on traffic management and control, traffic operations, intersection design and evaluation, and fuel consumption in the context of urban traffic management.
September 1968 - August 1975
Karadeniz Technical University
Position
  • Research Assistant
Description
  • Responsible for teaching and research in Road Design, Traffic Engineering and Transport Planning areas.
Education
September 1970 - March 1974
University of Leeds
Field of study
  • Transportation Engineering
October 1963 - July 1968
Istanbul Technical University
Field of study
  • Civil Engineering

Publications

Publications (147)
Conference Paper
Full-text available
In an earlier paper, the author presented an assessment of the roundabout capacity model given in the Highway Capacity Manual 2010 (HCM 2010) including discussions of lower capacity of roundabouts in the USA compared with Australian and UK roundabouts and the issue of possible increases in roundabout capacities in the USA over time due to changes i...
Conference Paper
Full-text available
This paper presents the results of a detailed comparison of two roundabout capacity models, namely a model developed by the first author of this paper based on her research conducted in Poland (referred to as the Macioszek model) and the model used in the SIDRA INTERSECTION software based on roundabout research conducted in Australia (referred to a...
Technical Report
Full-text available
This glossary has been prepared to include the terminology of the SIDRA INTERSECTION software. The sources used in preparing this document are the SIDRA INTERSECTION User Guide (2017), the Australian AUSTROADS Glossary, AP-C87-15 (2015) and the US Highway Capacity Manual Edition 6 Glossary (2016). This unique glossary includes many terms that are n...
Article
Full-text available
This short document presents a table comparing main features of three roundabout capacity models, namely the Australian model as implemented in the SIDRA INTERSECTION software, the HCM Edition 6 model described in Chapter 22 of the Highway Capacity Manual Edition 6, and the UK TRL model implemented in the RODEL and ARCADY software. The HCM Edition...
Article
Full-text available
This paper compares two analytical approaches for modelling signalised intersection networks in relation to the assessment of signal coordination quality as a fundamental element of network performance analysis. These are (i) the traditional model based on using “lane groups” or “links” through aggregation of individual lane conditions, and (ii) a...
Technical Report
Full-text available
This technical note and conference presentation give the results of an investigation to assess basic exponential (non-linear) and linear model forms used in practice for roundabout capacity estimation. Best fit regression and anchored regression analyses were carried out using the HCM single-lane roundabout capacity research data. The full dataset...
Technical Report
Full-text available
This technical note presents an investigation to explore if a linear capacity model can be derived as a gap-acceptance capacity model assuming a uniform or linear arrival headway distribution of the opposing traffic stream. The uniform and linear arrival headway distributions are introduced and the gap-acceptance capacity models based on these head...
Conference Paper
Full-text available
This conference presentation describes an extended version of the HCM Edition 6 Roundabout Capacity Model. As roundabouts become more widely adopted, a greater variety of multi-lane configurations and more frequent use of slip/bypass lanes are considered in design proposals. The HCM Edition 6 Extended Roundabout Capacity Model application in SIDRA...
Data
This Excel application presents a method for field surveys of Critical Gap (Headway) and Follow-up Headway which are the key parameters in the SIDRA gap acceptance capacity and performance models for roundabouts, intersections controlled by two-way stop and give-way / yield signs and unsignalised pedestrian crossings. The method can also be used fo...
Data
This Excel application presents a method for field surveys of Back of Queue and Queue at Start of Green or Queue at Start of Gap for signalised and unsignalised intersections, interchanges and pedestrian crossings. Queue at Start of Gap is for roundabouts, sign-controlled intersections and pedestrian crossings. For model calibration and validation...
Data
This Excel application presents a method for field surveys of Saturation Flow which is the key parameter in the SIDRA capacity and performance models for signalised intersections, interchanges and signalised pedestrian crossings. The associated Start Loss and End Gain parameters as well as an Equivalent SCATS MF (Maximum Flow) parameter are also de...
Technical Report
Full-text available
This technical note presents a critical review of the Austroads Report AP-R621-20 (Building Transport Modelling Management Capability) for project managers, modelling guide developers and modellers using analytical and simulation software for transport and traffic modelling. The review recommends that Austroads undertakes a major revision of this r...
Presentation
Full-text available
Models in software applications are becoming increasingly more sophisticated. Artificial Intelligence becoming visible in all areas of our lives. Is this making modellers smarter or are they left behind? How is all this affecting the use of models, interpreting outputs, handling uncertainties in model results and translating model outputs into prac...
Chapter
Gap-acceptance theory has been used widely for estimation of capacity at unsignalised roundabouts and two-way sign-controlled intersections. This paper discusses the use of the gap-acceptance method beyond modelling capacity. The author has developed gap acceptance capacity and performance models by signal analogy, including the estimation of delay...
Book
This book offers a collection of guidelines that will be particularly useful to those making decisions concerning roundabouts as safe and modern solutions in transport networks and systems. The decision-making support systems described here will interest those who face the challenge of finding solutions to problems concerning modern transport syste...
Presentation
Full-text available
Common Control Group is a SIDRA INTERSECTION software term used for a group of signalised intersections controlled by a single signal controller. This is relevant to the modelling of signalised paired (closely-spaced) intersections and interchanges such as staggered T intersections, freeway interchanges, intersections with median area controlled by...
Conference Paper
Full-text available
Common Control Group is a SIDRA INTERSECTION software term used for a group of signalised intersections controlled by a single signal controller. This is relevant to the modelling of signalised paired (closely-spaced) intersections such as staggered T intersections, freeway interchanges, intersections with median area controlled by signals, fully-s...
Presentation
Full-text available
The SIDRA INTERSECTION network model is largely built on the sound foundation of the lane-based methodology used in the single intersection model proven via research and used in practice during the last three decades. The network model elements used beyond single intersection modelling are discussed in this presentation. List of relevant documentat...
Conference Paper
Full-text available
Alternative intersection and interchange treatments used in the USA and other countries include Diverging (Double Crossover) Diamond Interchange, Displaced Left-Turn Intersection, Median U-Turn Intersection, Restricted Crossing U-Turn Intersection, and Continuous Flow Intersection. This presentation discusses the modelling of alternative intersecti...
Conference Paper
Full-text available
This presentation discusses main features of the network signal timing methodology which has been under development for the SIDRA INTERSECTION software (current Version 6.1 and the forthcoming Version 7). Direct elements of the network signal timing method includes lane-based second-by-second-platoon model using signal offsets, network cycle time a...
Conference Paper
This presentation discusses main features of the network signal timing methodology which has been under development for the SIDRA INTERSECTION software (current Version 6.1 and the forthcoming Version 7). Direct elements of the network signal timing method includes lane-based second-by-second-platoon model using signal offsets, network cycle time a...
Conference Paper
Full-text available
A lane-based signal platoon progression model has been developed for estimating performance measures as a function of signal offsets, geometric design and flow conditions. the model takes into account midblock lane changes that apply to signal platoon patterns. This particularly important in evaluating closely-spaced intersections with high demand...
Conference Paper
Full-text available
This paper presents results of the study of a road corridor in the historical city of Lucca, Tuscany, Italy. The corridor is about 1.5 km with seven different intersections along the corridor, including signalised and two-way stop controlled intersections and roundabouts. SIDRA INTERSECTION network model was used to analyze two scenarious; namely,...
Conference Paper
Full-text available
This presentation discusses various aspects of roundabouts in Australia and gives a detailed summary of the main features of roundabout capacity and performance models for intersection and networks used in the SIDRA INTERSECTION software.
Conference Paper
Full-text available
The modelling of signal platoon patterns is further enhanced by using the Movement Class facility of the SIDRA INTERSECTION software. This is implemented by assigning two types of movements negotiating the network to Special Movement Classes, namely; (i) Through movements at external approaches which become turning movements at downstream internal...
Conference Paper
Full-text available
An analytical lane-based method for determining platoon patterns at closely-spaced signalised intersections is discussed. The method has been developed for the SIDRA INTERSECTION software. The traditional network models using "links" or "lane groups" based on aggregation of individual lane conditions cannot provide sufficient information about depa...
Conference Paper
Full-text available
Measuring and assessing traffic congestion can be a difficult task in practice. This paper presents a case study investigating a highly congested signalized intersection in Melbourne. This is the intersection of Alexandra Parade and Wellington Street which has long queues on the westbound approach of the intersection extending upstream onto the Eas...
Data
Difficulties in measuring and assessing traffic congestion in practice is discussed.
Conference Paper
Full-text available
Estimation of fuel consumption and pollutant emissions for evaluating road traffic conditions is useful for environmental assessment in traffic design, operations and planning. This also forms the basis of operating cost modelling.Fuel consumption (CO2, CO, HC, NOx) models with four levels of aggregation for traffic engineering and transportation p...
Conference Paper
Full-text available
This paper discusses two aspects of modeling roundabout corridors: (i) a lane- based model of queue spillback, i.e. blockage of upstream lanes by queues formed in downstream lanes and the resulting capacity reduction in these lanes, and (ii) a model of the effect of upstream signals on the capacity and performance of a roundabout located downstream...
Conference Paper
Full-text available
This paper describes a lane-based micro-analytical model and demonstrates it using a detailed example of staggered -T roundabouts. The model has been developed recently and implemented in the SIDRA INTERSECTION software Version 6. Two fundamental elements of the model are (i) determining the backward spread of congestion as queues on downstream lan...
Conference Paper
Full-text available
The capacity, performance and level of service assessment of intersections controlled by stop and give-way signs has special importance in the context of traffic impact assessment where the choice of sign-controlled intersections rather than roundabouts or signalized intersections can be controversial due to significant cost differences. Such contr...
Conference Paper
Full-text available
This paper discusses the gap acceptance parameters recommended by the Austroads Road Design and Traffic Management Guides and the US Highway Capacity Manual; and describes a new method developed by the SIDRA INTERSECTION software for determining the critical gap and follow-up headway parameters for two-way stop and give-way sign controlled intersec...
Data
Full-text available
Estimation of fuel consumption and pollutant emissions for evaluating traffic conditions is useful for environmental assessment in traffic design, operations and planning. This also forms the basis of operating cost modelling. Fuel consumption and emission (CO2, CO, HC, NOx) models of four levels of aggregation were developed by the first author an...
Conference Paper
Full-text available
This presentation highlights various aspects of Roundabouts in AUSTRALIA and NEW ZEALAND in response to the following objective of International Roundabout Design and Capacity Seminar: Present an overview of typical roundabout designs in urban and rural environments and treatments of bicycles and pedestrians, capacity and level-of-service methods u...
Article
Full-text available
Roundabout metering signals help to create gaps in the circulating stream to solve the problem of excessive queuing and delays caused by unbalanced flow patterns and high demand flow levels. This paper gives a brief summary of the control of roundabouts using metering signals and describes the basic concepts of an analytical model of the operation...
Conference Paper
Full-text available
This paper presents an assessment of the roundabout capacity model given in the new Highway Capacity Manual 2010 (HCM 2010) with a focus in its use in the SIDRA INTERSECTION software. The model which is based on US research on roundabouts (NCHRP 572) can be viewed as a non-linear empirical (regression) model with a theoretical basis in gap-acceptan...
Conference Paper
Full-text available
This paper considers three well-known analytical models of roundabout capacity, and discusses some common and differing aspects of these models. The models considered are the US Highway Capacity Manual 2010 (HCM 2010) model, Australian SIDRA INTERSECTION model and the UK TRL (linear regression) model. These models have some common features as well...
Article
Full-text available
There has been some controversy in relation to the lane-based gap-acceptance model used in SIDRA INTERSECTION software vs the approach-based linear regression (UK TRL "empirical") model used in RODEL and ARCADY software for estimating the capacity of roundabouts. This is relevant to the US scene where roundabouts are relatively new. This detailed d...
Article
Full-text available
Results of research on roundabouts in the United States are presented in the NCHRP Report 572. The findings and recommendations of this report are important as they will be the basis of the 2010 Highway Capacity Manual methodology for operational analysis of roundabouts. This paper discusses various findings and recommendations of the NCHRP Report...
Conference Paper
Full-text available
This paper presents a collation of comments received from Australian traffic and transport professionals in response to a survey about the current status of roundabouts in Australia. The survey posed questions related to the extent to which roundabouts are being built, replacement of roundabouts with signals or signals with roundabouts, use of roun...
Conference Paper
Full-text available
A major project was undertaken for VicRoads, the state transport authority in Victoria, 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 validat...
Conference Paper
Full-text available
Analytical models use traffic stream capacity as a basic parameter in traffic performance estimation. Traffic characteristics that affect capacity are not often clearly explained or understood. This causes difficulties in practice when professional judgement has to be used in interpreting output and calibrating models for specific applications. The...
Conference Paper
This paper presents a collation of comments received from Australian traffic and transport professionals in response to a survey about the current status of roundabouts in Australia. The survey posed questions related to the extent to which roundabouts are being built, replacement of roundabouts with signals or signals with roundabouts, use of roun...
Conference Paper
Full-text available
Gap-acceptance capacity models apply to the analysis of minor movements at two-way stop and give-way (yield) sign-controlled intersections, entry streams at roundabouts and opposed (permitted) turns at signalised intersections. The same modelling principles apply to all these cases with different model parameters representing the intersection geome...
Conference Paper
Full-text available
This Presentation discusses relationships between microsimulation and analytical models.
Conference Paper
Full-text available
Estimation of operating cost, fuel consumption and pollutant emissions for evaluating intersection traffic conditions is useful for design, operations and planning purposes in traffic management. A four-mode elemental (drive cycle) model is used for estimating fuel consumption, emissions and operating cost. The drive cycles vary significantly for d...
Article
Full-text available
There are many examples of roundabouts with unbalanced flow patterns in Australia, where part-time roundabout metering signals are used to create gaps in the circulating stream in order to solve the problem of excessive queuing and delays at approaches affected by highly directional flows. The use of metering signals is a cost-effective measure to...
Article
Full-text available
A time-dependent speed-flow model based on queuing theory concepts (referred to as Akçelik's function in the literature) was previously used to develop alternative versions of the HCM speed-flow models for basic freeway segments, multilane highways and urban streets. This paper introduces an explicit model that describes in-stream vehicle interacti...
Article
Full-text available
Akçelik's time-dependent speed - flow model based on queuing theory concepts is used to develop alternative versions of the HCM speed - flow models for basic freeway segments, multilane highways and urban streets. The corresponding travel time - flow models show that higher-quality facilities have lower levels of bunching delays. A version of the s...
Conference Paper
Full-text available
This paper discusses issues related to calibration of models for analyzing roundabout capacity and performance. Two basic calibration methods that can be used for gap-acceptance and linear regression methods are described. A case study is presented to compare capacity estimates from the gap-acceptance and linear-regression methods, including a cali...
Conference Paper
Full-text available
This paper describes a method for the analysis of capacity and performance of roundabouts operating with metering signals. When low capacity conditions occur during peak demand flow periods, for example due to unbalanced flow patterns, the use of metering signals is a cost-effective measure to avoid the need for a fully-signalized intersection trea...
Article
The roundabout capacity analysis method used in aaSIDRA was originally based on the method described in ARRB Special Report SR 45 which was introduced into aaSIDRA with some variations and extensions. The SR 45 method was also incorporated into the AUSTROADS (1993) Roundabout Guide with some minor modifications. Subsequently, significant enhancemen...
Article
Full-text available
The roundabout capacity analysis method used in aaSIDRA was originally based on the method described in ARRB Special Report SR 45 (Troutbeck 1989) which was introduced into aaSIDRA with some variations and extensions (Akçelik and Troutbeck 1991). The SR 45 method was also incorporated into the AUSTROADS (1993) Roundabout Guide with some minor modif...
Article
Full-text available
An improved understanding of the effect of origin-destination demand pattern of traffic on roundabout capacity and level of service will help towards designing new roundabouts that will cope with future increases in demand levels and solving any problems resulting from unbalanced flow patterns at existing roundabouts. Case studies are presented to...
Conference Paper
Full-text available
Estimation of operating cost, fuel consumption and pollutant emissions for evaluating intersection and mid-block traffic conditions is useful for design, operations and planning purposes in traffic management. This paper describes the method to model operating cost, fuel consumption and emissions (CO2, CO, HC, NOx) in the aaSIDRA intersection analy...
Technical Report
Full-text available
This technical report explains the uninterrupted travel speed concept, and describes the HCM speed-flow models for basic freeway segments and multilane highways as well as for the running time component of the HCM travel-speed model for urban streets.
Article
Full-text available
There has been some controversy about capacity estimates from the gap-acceptance based Australian and Highway Capacity Manual methods and the linear-regression based UK (empirical) method. This paper presents a single-lane roundabout case study from the United States to compare capacity estimates from these analytical models. Some contradictory res...
Conference Paper
Full-text available
New models for estimating negotiation radius, distance and speed values of through and turning vehicles at roundabouts were introduced in aaSIDRA Version 2. The intersection negotiation parameters are important in determining geometric delays, fuel consumption, pollutant emission and operating cost values for traffic using roundabouts. The paper gi...
Article
This paper describes the exponential queue discharge flow rate and speed models, and presents a summary of model calibration results based on data from 18 intersections in Melbourne and Sydney, Australia. Relationships among saturation headway and speed, jam spacing, queue departure response time, queue departure wave speed and acceleration charact...
Chapter
This paper describes the exponential queue discharge flow rate and speed models, and presents a summary of model calibration results based on data from 18 intersections in Melbourne and Sydney, Australia. Presented are relationships among saturation headway and speed, jam spacing, queue departure response time, queue departure wave speed and accele...
Technical Report
Full-text available
This report presents findings of an investigation of pedestrian movements characteristics at three pedestrian actuated mid-block signalised crossings in Melbourne, Australia. Two surveys were carried out at each site, on on a weekday and one on a weekend. A survey method was developed and used as part of the project.
Conference Paper
Full-text available
This paper presents findings of an investigation of pedestrian movement characteristics at intersection signalised crossings. The main objective of the study was to obtain information on pedestrian crossing speeds used for signal timing purposes, and pedestrian movement start loss and clearance time gain parameters used in pedestrian delay calculat...
Article
Full-text available
The effectiveness of SCATS Master Isolated (SMI) control for non-coordinated signalised intersections was evaluated using vehicle-by-vehicle simulation including an evaluation of the effects of detector failure, as well as field surveys. Various SCATS-like adaptive control algorithms were developed and tested through extensive simulation tests with...
Technical Report
Full-text available
A major improvement in the latest edition of the US Highway Capacity Manual is the introduction of a back of queue model for signalised intersections. The model was derived by simplification of the more general form used in the aaSIDRA software. The report describes the HCM 2000 queue model fully, and presents comparisons with microscopic simulatio...
Article
Full-text available
Modelling of acceleration and deceleration distances and times associated with speed change cycles under normal driving conditions is essential for the analysis of operating cost, fuel consumption and pollutant emissions, as well as for determining geometric, stopped and queuing components of overall delay. Similarly, modelling of acceleration and...
Article
Full-text available
Such folklore consists of generalisations by its nature, and can be helpful if used with the understanding that various points may not be valid in specific situations, and some information may get outdated as traffic characteristics change in time. The authors advised the readers to "use the material as a good guide, and refer to the appropriate st...
Article
Full-text available
This 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...
Article
Full-text available
This Report presents findings of a study of fundamental characteristics of freeway traffic flows 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 method...
Article
Full-text available
Presentation at the International Conference on Modern Roundabouts (1998), Loveland, Colorado, USA
Article
Full-text available
The results of an evaluation of three analytical delay models for unsignalised intersections are presented. The delay models studied are the Highway Capacity Manual Chapter 10 (HCM 94) Model, the Akҫelik - Troutbeck model, and the SIDRA 5 model. These models are applicable to sign-controlled intersections and roundabouts. The evaluation work was re...
Article
Full-text available
Results of extensive research on actuated signal control methods are presented. A method for predicting actuated signal timings, and analytical models for predicting various performance statistics (delay, queue length, queue clearance time, proportion queued), that are implemented in the SIDRA software package are described. With actuated signal ti...
Article
Full-text available
This paper was prepared in response to two articles, "ARCADY Health Warning: Account for unequal lane usage or risk damaging the Public Purse" by B. Chard, and "Modelling flares at traffic signal-controlled junctions" B.F. Simmonite and P. Moore. These articles address problems associated with the "approach" method of traffic modelling which lumps...