Introducing SIDRA INTERSECTION 3
(General presentation including New Features 2Mb)

Datasheet: SIDRA TRIP
Product Information Flyer (776KB)

AKÇELIK, R. (2007).  A Review of Gap-Acceptance Capacity Models. Paper presented at the 29th Conference of Australian Institutes of Transport Research (CAITR 2007), Adelaide, December 2007. 

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 geometry, control and driver behaviour at different traffic facilities. This paper presents a review of some well-known analytical models that use bunched exponential and simple negative exponential distribution of headways in the opposing stream. Different bunching models are considered including the latest model used in SIDRA INTERSECTION. The capacity estimates from different models are compared. Research recommendations are included.  The paper includes a survey method for follow-up headway and critical gap parameters. 

Akcelik and Associates Review of Activities During 2007.
Paper presented at the 29th Conference of Australian Institutes of Transport Research (CAITR 2007), Adelaide, December 2007.
(2.5MB) 

AKÇELIK, R. (2007). Microsimulation and Analytical Models for Traffic Engineering. Presentation at the ARRB - AUSTROADS Microsimulation Forum 19-20 Sep 2007.
(1.5 Mb) Made available: 22 Sep 2007.

This presentation discusses relationships between microsimulation and analytical models. 

The following paper is recommended in relation to this presentation:
Akçelik, R., and Besley M. (2001).  Microsimulation and analytical methods for modelling urban traffic.  Paper presented at the Conference on Advance Modeling Techniques and Quality of Service in Highway Capacity Analysis, Truckee, California, USA. (231KB). 

AKÇELIK, R. (2007). Roundabout Model Comparison Table.  Akcelik and Associates Pty Ltd, Melbourne, Australia.  (80KB)  Updated: 3 July 2007

This two-page document presents a table comparing main features of three roundabout models, namely the Australian model as implemented in the aaSIDRA software, the UK (TRL) model as implemented in the RODEL and ARCADY software packages, and the HCM model (current HCM 2000 model as well as the NCHRP 3-65 research results).  Note that the NCHRP 3-65 models are preliminary only (as presented at the TRB Roundabout Conference, Vail, CO, May 2005).

AKÇELIK, R. (2006).  Operating Cost, Fuel Consumption and Pollutant Emission Savings at a Roundabout with METERING SIGNALS.  Paper presented at the ARRB 22nd Conference, Canberra, 29 Oct - 2 Nov 2006.  Updated: 22 October 2007.

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 different intersection types (roundabout, signalised, sign-controlled), for different signal phasings and timings, and for different congestion levels.  A case study is presented comparing a roundabout with and without metering signals in terms of operating cost, fuel consumption and pollutant emissions as well as delay and degree of saturation.

AKÇELIK, R. (2006).  Speed - Flow and Bunching Models for Uninterrupted Flows.  Paper presented at the Transportation Research Board 5th International Symposium on Highway Capacity and Quality of Service, Yokohama, Japan, July 2006.

(170KB) Made available: 24 Aug 2006.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 speed - flow model that describes in-stream vehicle interactions and resulting queuing in terms of traffic bunching characteristics is introduced.  Speed - flow and headway distribution models for uninterrupted traffic streams are integrated using a common traffic delay parameter.  A new model of the proportion of bunched vehicles is proposed for the bunched exponential model of headway distribution.  The driver response time parameter at capacity flow is discussed.  A model for forced flow conditions is developed, and unsaturated and forced flow conditions are contrasted in relation to determining headway distributions.

Akcelik and Associates Review of Activities During 2006.
Paper presented at the 28th Conference of Australian Institutes of Transport Research (CAITR 2006), Sydney, 6-8 December 2006. 
(170KB) 

AKÇELIK, R. and BESLEY, M. (2004).  Differences Between the AUSTROADS Roundabout Guide and aaSIDRA Roundabout Analysis Methods.  

Paper presented at the 26th Conference of Australian Institutes of Transport Research (CAITR 2004), Melbourne, Dec 2004, and published in Road & Transport Research 14(1).  
(310KB)  Made available: 4 Aug 05 This paper presents a summary of the differences between the AUSTROADS (1993) Roundabout Guide and aaSIDRA methods for roundabout capacity and performance analysis, and discusses some important aspects of the analysis method where significant differences exist.

AKÇELIK, R. (2005).  Roundabout Model Calibration Issues and a Case Study.  Paper presented at the TRB National Roundabout Conference, Vail, Colorado, USA, May 2005. (0.3MB) Updated: 3 June 2005

Presentation (1.0MB)  Updated: 3 June 2005

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 calibration example.  A traffic model framework is presented to help with assessment of traffic models in a general framework, considering all aspects of models relevant to roundabout operation.  While the discussion focuses on analytical models, the issues raised are also relevant to microsimulation models.  Discussion on roundabout models should not concentrate on capacity alone, and instead, modeling requirements for estimating both capacity and performance (delay, queue length, etc) should be considered together.  Various aspects of field observations relevant to the calibration effort are discussed.  These include issues related to the definition and measurement of capacity, delay and queue length, including the effect of unequal lane utilization.  Delay criteria for level of service definition are also discussed.  Further aspects of model calibration discussed include the environment factor, adjustment for the arrival flow / circulating flow ratio, lane utilization factor, heavy vehicle factor, driver response time and calibration of models for operating cost, emissions and fuel consumption.

AKÇELIK, R. (2005).  Capacity and Performance Analysis of Roundabout Metering Signals.  Paper presented at the TRB National Roundabout Conference, Vail, Colorado, USA, May 2005.   (1.0MB) Updated: 3 June 2005.

Presentation (2.3MB)  Updated: 3 June 2005.

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 treatment.  Roundabout metering signals are often installed on selected roundabout approaches and used on a part-time basis since they are required only when heavy demand conditions occur during peak periods.  Metering signals have been used to alleviate the problem of excessive delay and queuing by creating gaps in the circulating stream.  The basic principles of the operation of roundabout metering signals are explained.  Case studies of various roundabouts where metering signals were used, or considered for use, have been presented in previous papers by the author.  This paper presents the results of analysis of one of these case studies when operating with metering signals.

Stops & Goes of Traffic Signals    (0.4MB)  Transfund New Zealand (now part of Land Transport New Zealand) funded the development of a signal audit methodology in order to examine the safety and efficiency of traffic signals. A representative number of signal installations across nine territorial local authorities (TLAs) were audited. Stops & Goes of Traffic Signals presents findings of this study.

Akcelik and Associates Review of Activities During 2004.
Paper presented at the 26th Conference of Australian Institutes of Transport Research (CAITR 2004), Clayton, Melbourne, 8-10 December 2004. 
(580KB) 

This paper presents a summary of some of the activities undertaken by Akcelik and Associates during 2004.  These include aaSIDRA 2.1 release and further development, aaSIDRA software training, aaMOTION software development, Workshops on AUSTROADS Traffic Signals Guide, roundabout analysis methods, and other activities. 

AKÇELIK, R. (2004).  Roundabouts with Unbalanced Flow Patterns.  Paper presented at the ITE 2004 Annual Meeting, Lake Buena Vista, Florida, USA, Aug 2004. 
(0.9MB) Updated: 6 May 2005.

Presentation (1.4MB)  Updated: 25 Aug 2004.

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 show that roundabout capacity and level of service depend not only on the circulating flow rate but also the characteristics of approach flows contributing to the circulating flow.  The amount of queuing on the approach road, circulating lane use, priority sharing and priority emphasis are the factors that need to be taken into account.  Dominant circulating flows that originate mostly from a single approach with high levels of queuing and unequal lane use (with most vehicles in one lane), cause priority emphasis and reduce the entry capacity significantly.  This is evident from the use of part-time metering signals under peak demand conditions in order to alleviate the problem of excessive delay and queuing by creating gaps in the circulating stream.  The Australian roundabout and traffic signal guides acknowledge the problem and discuss the use of metering signals.

AKÇELIK, R. (2003).  A Roundabout Case Study Comparing Capacity Estimates from Alternative Analytical Models.  Paper presented at the 2nd Urban Street Symposium, Anaheim, California, USA, 28-30 July 2003.  (760KB). Revised 15 Jun 2004

A single-lane roundabout case study from the United States is presented to compare capacity estimates from various analytical models.  Some contradictory results that can be obtained from these models are highlighted and reasons for differences are discussed.  Such systematic differences have important design implications.  The paper discusses why the TRL Linear Regression model may underestimate capacity for low circulating flows and overestimate capacity for high circulating flows.  The case study displays an unbalanced flow pattern which contributes to significant differences between models.

Speed-Flow and Bunching Relationships for Uninterrupted Flows (330KB).  Paper presented at the 25th Conference of Australian Institutes of Transport Research (CAITR 2003), University of South Australia, Adelaide, Australia, 3-5 December 2003.  Made available: 22 Dec 2003.

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 interactions and resulting queuing in terms of traffic bunching characteristics.  For this purpose, the bunched exponential model of the distribution of vehicle headways is used.  A new model of the proportion of bunched vehicles is proposed.  The model uses the delay parameter of Akçelik's speed - flow model as a bunching parameter, thus linking the bunching and speed-flow models.  The paper also discusses the driver response time parameter at capacity flow.  A model for forced flow conditions is then developed, and unsaturated and forced flow conditions are contrasted for the purpose of determining headway distributions.  The paper also discusses application of the new bunching model and the associated speed-flow model to roundabout circulating streams.

Operating cost, fuel consumption, and emission models in aaSIDRA and aaMotion (270KB).  Paper presented at the 25th Conference of Australian Institutes of Transport Research (CAITR 2003), University of South Australia, Adelaide, Australia, 3-5 December 2003.  Updated: 4 Dec 2007.

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 analysis and aaMotion trip / drive-cycle simulator software packages developed by Akcelik & Associates.  aaMotion has not been released yet. 

Akcelik and Associates Review of Activities during 2003. (620KB).  Paper presented at the 25th Conference of Australian Institutes of Transport Research (CAITR 2003), University of South Australia, Adelaide, Australia, 3-5 December 2003.  Made available: 22 Dec 2003.

This paper presents a summary of some of the activities undertaken by Akcelik and Associates during 2003.  These include aaSIDRA and aaMotion software development, aaSIDRA training, AUSTROADS Guide to Traffic Engineering Part 7 - Traffic Signals publication and workshops, roundabout capacity model development and roundabout case studies for unbalanced flows, and further work on speed-flow and bunching models.

Speed-Flow Models for Uninterrupted Traffic Facilities.  (1015KB) Akcelik and Associates Technical Report.   Updated: 2 Dec 2003.

The 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. The HCM speed-flow models are given for undersaturated conditions on these uninterrupted-flow facilities.  Multilane highway analysis is qualified as relevant to "rural and suburban" highways.  Urban roads with signalized intersections spaced at 3 km or more fall into this category, otherwise they are classified as urban streets.  The aaSIDRA speed-flow relationships for uninterrupted movements were calibrated against the US Highway Capacity Manual speed-flow models.  This effort indicated various unexpected characteristics of the HCM 2000 models.  The report presents the results of an investigation of issues of concern with the HCM models.  A proposed solution based on the use of "Akcelik's" speed-flow function is presented. Akçelik's function, which applies to both undersaturated and oversaturated conditions is described in detail.

Calibration of the bunched exponential distribution of arrival headways. (900KB).  Reprint of 1994 paper.  Made available: 15 Jun 2003.

The estimation of arrival headways is fundamental to the modelling of gap acceptance processes for estimating capacities of sign-controlled traffic streams, roundabout entry streams and filter turns at signalised intersections.  It is also essential in modelling both vehicle-actuated signal timings and queuing at all types of intersections for performance prediction.  This paper considers a class of arrival headway distributions known as negative exponential, shifted negative exponential and bunched exponential.  A description of the bunched exponential arrival headway distribution is presented, and the results of its calibration using real-life data for single-lane traffic streams and simulation data for multi-lane streams are given.  Examples of gap-acceptance capacities and delays predicted by different exponential headway distributions are also presented. 

Estimating negotiation radius, distance and speed for vehicles using roundabouts. (270KB).  Paper presented at the 24th Conference of Australian Institutes of Transport Research (CAITR 2002), University of New South Wales, Sydney, Australia, 4-6 December 2002.  Updated: 14 Oct 2004.

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 gives figures showing simplified constructions of vehicle paths for through, left-turning and right-turning vehicles.  The method allows for path smoothing by drivers.  The safe negotiation speed formula uses a side friction factor that is a function of vehicle mass.  Graphs showing the side friction factor as a function of the vehicle mass, and negotiation speed as a function of the turn radius are presented.  The negotiation radius, distance and speed values as a function of the roundabouts size, and graphs showing the sensitivity of geometric delay to roundabout size and approach and exit cruise speeds are presented.

Akcelik and Associates Review of Activities during 2002. (1250KB).  Paper presented at the 24th Conference of Australian Institutes of Transport Research (CAITR 2002), , University of New South Wales, Sydney, Australia, 4-6 December 2002.  Made available: 2 Dec 2002.

This paper presents a summary of some of the activities undertaken by Akcelik and Associates during 2002.  These include aaSIDRA version 2 release, software training, queue discharge characteristics at signalised intersections, vehicle motion simulator (aaMotion), roundabout capacity and performance, speed-flow models for uninterrupted  traffic facilities, and other activities.

AKÇELIK, R. and BESLEY, M. (2002).  Queue discharge flow and speed models for signalised intersections.  In: Transportation and Traffic Theory in the 21st Century, Proceedings of the 15th International Symposium on Transportation and Traffic Theory, Adelaide, 2002 (Edited by M.A.P. Taylor).  Pergamon, Elsevier Science Ltd, Oxford, UK, pp 99-118.

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 characteristics are presented. Implications of the queue discharge flow and speed models for adaptive signal control practice, namely the SCATS control parameters, optimum detector loop (detection zone) length and the gap setting parameter are discussed.

 

On the Validity of Some Traffic Engineering Folklore. Paper presented at the 22nd Conference of Australian Institutes of Transport Research (CAITR 2000), Ursula College, ANU Campus, Canberra, Australia, December 2000.   (308KB)

This paper presents commentary on selected points from an earlier article titled "Traffic Engineering Folklore" which presented "a summary of quick and easy approximations to traffic related problems" based on an Australia-wide survey of traffic professionals in the 1980s. The comments given here are based on information from recent research and detailed analytical and computer-based traffic modelling.  The points covered relate to vehicle dimensions, capacities of uninterrupted and interrupted facilities, traffic flow characteristics, vehicle and pedestrian speeds, signalised intersections and roundabouts.  It is shown that most points considered are generally valid as approximations.  Suggestions are made for revising the statements analysed, and additional statements are presented for consideration.

Three-laning a two-lane roundabout - the outcomes. paper by O'BRIEN, A., AKÇELIK, R., WILLIAMSON, D. and PANTAS, T. Compendium of Technical Papers (CD). 
67th Annual Meeting of the Institution of Transportation Engineers, Boston, USA, (1997).  (500KB)

Using aaSIDRA, VicRoads engineers redesigned a highly congested two-lane roundabout in Melbourne, Australia as a three-lane roundabout eliminating persistent congestion.  Detailed field surveys were conducted before and after the reconstruction.  This article presents detailed information about this study.

Acceleration and deceleration models. (270KB) Paper presented at the 23rd Conference of Australian Institutes of Transport Research (CAITR 2001), Monash University, Melbourne. Revised version. Made available: 11 Jul 2002

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 deceleration characteristics of individual vehicles is a key issue in relation to the accuracy of microsimulation models. This paper describes the acceleration and deceleration models used in the aaSIDRA software for intersection analysis, and emphasises the research needs for better model calibration considering different vehicle types, specific traffic facilities, different traffic demand levels, different road types, and a wide range of initial and final speeds.

Akcelik and Associates Review of Activities during 2001. (299KB) Paper presented at the 23rd Conference of Australian Institutes of Transport Research (CAITR 2001), Monash University, Melbourne. Made available: 21 Dec 2001.

This paper presents a summary of some of the activities undertaken by Akcelik and Associates during 2001.  These include revision of AUSTROADS Guide to Traffic Engineering Part 7 - Traffic Signals, pedestrian research, microsimulation and analytical models, Highway Capacity Manual 2000, and aaSIDRA software development and training.

An Investigation of Pedestrian Movement Characteristics at Mid-Block Signalised Crossings  (400KB) Akcelik and Associates Technical Report.  Made available: 21 Dec 2001.

This report presents findings of an investigation pedestrian movement characteristics at three pedestrian actuated mid-block signalised crossings in Melbourne, Australia.  Two surveys were carried out at each site, one on a weekday and one on the weekend.  A survey method was developed and used as part of this project.  The main objective of the study was to obtain information on crossing speeds of pedestrians for signal timing purposes, and pedestrian movement start loss and clearance time gain parameters for pedestrian delay and queue calculations.  Other information obtained from surveys included the proportions of pedestrians using different signal intervals (Walk, Flashing Don't Walk).  The study also investigated characteristics of pedestrians with walking difficulties.  The 15th percentile speed for all sites combined is very close to the general design speed of 1.2 m/s recommended by the Australian and US design guides, and the 15th percentile speed for pedestrians with walking difficulty is very close to the design speed of 1.0 m/s recommended by the Australian and US design guides for sites with higher populations of slower pedestrians. 

Pedestrian Movement Characteristics at Signalised Intersections. (244KB) Paper presented at the 23rd Conference of Australian Institutes of Transport Research (CAITR 2001), Monash University, Melbourne. Made available: 19 Dec 2001.

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 calculations.  Surveys were conducted at four signalised intersections of four-lane roads in busy suburban shopping strips. Two surveys were conducted at each site, one on the weekend and one on a weekday.  Pedestrian crossing speeds for different sites, weekdays and weekends, queued and unqueued pedestrians, and pedestrians with and without walking difficulty are presented.  The results of this study are compared with the findings from the study of pedestrians at mid-block signalised crossings.

HCM 2000 Back of Queue Model for Signalised Intersections (220KB) Akcelik and Associates technical report that provides background information on the HCM 2000 queue model for signalised intersections. Made available: 23 Nov 2001.

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 simulation data, real-life data and aaSIDRA estimates.  The theoretical background to the development of the model is discussed, and a method for determining model parameters in the case of unequal lane utilisation is given. The model uses progression factors for platooned arrivals consistent with the HCM 2000 delay model.  The model can estimate the average back of queue, as well as 70th, 85th, 90th, 95th and 98th percentile queue values.  A model to predict the queue clearance time is also given for use in the opposed (permitted) turn model and the actuated signal timing method. The back of queue measure is useful for identifying spillback conditions (i.e. the blockage of available queue storage distance).  The queue storage ratio measure is presented for this purpose.  The queue model allows for an initial queued demand at the start of the flow period.

Progression Factors in the HCM 2000 Queue and Delay Models for Traffic Signals.  (270KB) Akcelik and Associates Technical Report to enhance the application of the Highway Capacity Manual 2000 method for platooned arrivals. 
Made available: 6 Sep 2001.

This Technical Note specifies various conditions for use in implementing the HCM 2000 progression factors for delay and back of queue.  The progression factor equations are given, the implementation conditions (constraints) are explained, and the issue of large values of progression factors that may result under certain circumstances is discussed.  The method has been approved by the TRB Highway Capacity and Quality and Service Committee.  Also see HCM 2000 Queue Model.

Akçelik, R., and Besley M. (2001).  Microsimulation and analytical methods for modelling urban traffic.  Paper presented at the Conference on Advance Modeling Techniques and Quality of Service in Highway Capacity Analysis, Truckee, California, USA. (231KB).   Reprint with revisions.   Made available: 12 Oct 2001.

Microsimulation models can help with 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.  This paper focuses on compatibility between microsimulation methods and established analytical techniques that are used in traffic engineering.  Several key components of traffic models are discussed, and various recommendations are made, with a view to improving the practical usefulness of microsimulation models.  These include (i) the use of simulation for capacity analysis, (ii) modelling of queue discharge (saturation) flow rate, queue discharge speed and other queue discharge parameters at signalised intersections, and relating them to the general queuing, acceleration and car-following models used in microsimulation; (iii) modelling of gap-acceptance situations at all types of traffic facilities, and (iv) estimation of lane flows at intersection approaches, and relating this to lane changing models used in microsimulation. The consistency of definitions and measurement methods for traffic performance variables such as delay (stopped, geometric, etc) and queue length (cycle average and back of queue) is also discussed.  It is suggested that comparison of specific microsimulation and analytical model components is useful towards model benchmarking for evaluation of new and existing models.  Towards this end, a simple signalised intersection case is specified in sufficient detail to enable assessment of two basic traffic model components, namely queue discharge flow rate and lane flow distribution.  

An evaluation of SCATS Master Isolated control. (138KB) 
Reprint of 1998 paper.   Made available: 6 Sep 2001.

The well-known SCATS wide-area traffic control system has a unique feature for the control of a single non-coordinated signalised intersection known as SCATS Master Isolated control.  The effectiveness of this control was evaluated using microsimulation and field surveys.  Various SCATS-like adaptive control algorithms were developed and tested through extensive simulation tests with a wide range of demand flow patterns and a large number of control parameter combinations.  Traditional vehicle-actuated and fixed-time control were also evaluated.  The results for an algorithm that emulated the SCATS Master Isolated control, and the traditional vehicle-actuated control method are presented in this paper.  A new survey method was developed, trialed and used for field surveys.  The survey method produced a large number of timing, capacity and performance statistics.  The surveys produced results that were in line with the results of simulation studies. The overall conclusion was that SCATS Master Isolated control gives better intersection performance than traditional actuated signal control as indicated by lower delays and shorter queue lengths achieved with shorter cycle times.  Evaluation of the effects of detector failure indicated substantial benefits from the SCATS Master Isolated control in terms of all performance measures considered. 

Recent research on actuated signal timing and performance evaluation and its application in SIDRA 5. (263KB)   Reprint of 1997 paper.  Made available: 6 Sep 2001.

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 timings, equal degrees of saturation do not necessarily result, and the minor movements may get lower degrees of saturation than the major movements, indicating inefficient operation with long cycle times. Comparisons of SIDRA estimates of delay, back of queue and queue clearance time for actuated signals with those predicted by microsimulation as well as those observed at a real-life intersection are presented. 

On the estimation of lane flows for intersection analysis.  (180KB).  Reprint of Akcelik's 1989 paper.  Made available: 6 Sep 2001.

This article responds to the question "Which principle should be used as a basis for estimating lane flows at the approaches to an intersection, and how does this principle relate to the lane choice decisions of individual drivers? " .  Equal degree of saturation, equal average delay, minimum travel time, equal queue length principles are discussed.  Relationship between lane choice and route choice principles, interaction with signal timings, and relation to the Level of Service criteria are also considered. 

Lane-by-lane modelling of unequal lane use and flares at roundabouts and signalised intersections: the SIDRA solution (160KB).  Reprint of 1997 paper.

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 traffic in individual lanes of an intersection approach together. Chard demonstrates by means of case studies that "(the ARCADY model) can take no account of either unused or unequally used lanes or flared sections on roundabout entry approaches. Simmonite and Moore state that "the art of modelling (flared approaches) is difficult and, as such, often overlooked by practitioners".  This paper discusses important aspects of the two articles from the perspective of the lane-by-lane method and short lane model used in aaSIDRA for all types of intersection (signalised, roundabout, sign control).  SIDRA computations are heavily based on estimating lane flows, modelling traffic in shared lanes including any lane blockages, establishing any de facto (effective) exclusive lanes, determining reduced short lane capacities and any excess flows from short lanes into adjacent lanes.  

 

ARCADY Health Warning: Account for unequal lane usage or risk damaging the Public Purse! CHARD, B. (1997). Traffic Engineering and Control, 38(3), pp 122-132. 

Travel time functions for transport planning purposes: Davidson's function, its time-dependent form and an alternative travel time function (130KB). Reprint of Akcelik's 1991 paper.  Excel application is given below.

A travel time function proposed by Davidson for transport planning purposes has been subject to much discussion and efforts of calibration including some controversy over the meaning of its parameters.  This paper presents a time-dependent form of the original Davidson function, derived using the coordinate transformation technique.  The derivation of the original Davidson function is discussed.  A new travel time function is proposed as an alternative to Davidson's function.  In the proposed function, the delay parameter takes a meaning consistent with the formulae used for estimating intersection delays.  Both the steady-state and time-dependent forms of the new function are given.