Emerging Modelling Practices

David Nash, Traffinity - Use of SCATS MF to Calibrate SIDRA Saturation Flow

David Nash

Principal | Traffinity

David is Principal of Traffinity - a traffic engineering consultancy.  David has over 40 years of experience in traffic engineering, and spent most of his career working at VicRoads.  He has been a member of the Australian Standards and several Austroads committees.

Co-Author(s)

Rahmi Akcelik | SIDRA SOLUTIONS

Dr Rahmi Akcelik is Director of Akcelik and Associates Pty Ltd (trading as SIDRA SOLUTIONS) in Victoria. 

Mark Besley | SIDRA SOLUTIONS

Mark Besley is a Director of SIDRA SOLUTIONS in Victoria.
Mark is a scientist and software specialist who has worked in the traffic management area since 1980s. He has been making a significant contribution to the development of the SIDRA INTERSECTION software in collaboration with Dr Rahmi Akçelik during the last 30+ years.

He has trained several thousand professionals in over 300 workshops, courses, and seminars.

Mark has been involved in many aspects of research on traffic operations including traffic network models, incident detection, fuel consumption estimation, traffic data collection, and analysis.

Use of SCATS MF to Calibrate SIDRA Saturation Flow

Saturation Flow is fundamental to the analysis of signalised intersections.  There is an emerging trend for SIDRA users to modify the Basic Saturation Flow in modelling existing signalised intersections to match the value of Maximum Flow (MF) measured and recorded in SCATS.  

Saturation Flow and Maximum Flow are quite similar in concept, but one cannot be substituted for the other due to significant differences in how these parameters are measured and applied.

Misunderstandings of how Saturation Flow and Maximum Flow are related can have significant effect on delay and queue length estimates given by the model.  

This presentation explains how SCATS measures and records MF, and how Saturation Flow is used in modelling signalised intersections. The study has examined the MF values across intersections in Melbourne's inner, middle and outer suburbs, highlighting the types of lanes where the correlation between MF and Saturation Flow is weak due to highly variable queue discharge conditions from cycle to cycle.

The study has led to the development of a set of guidelines for using SCATS MF to calibrate the SIDRA Basic Saturation Flow for lanes where the correlation is likely to be strong.  

The model should still be allowed to apply automatic adjustments to take account of lane width, gradient, vehicle mix, pedestrian interference, shared lanes, short lanes and downstream queue blockages as they vary in alternative analysis scenarios modelled.  A caution is included about using SCATS MF in cases where the lane operates under different conditions during the day.

Ahmed Elsergany, Transport Canberra & City Services - Using Strategic Planning Methods for Evacuation Trip Distribution in Riverine Flood Disasters:  A Case Study in the Australian Capital Territory

Ahmed Elsergany

Assistant Director | Transport Canberra & City Services

Ahmed is an Assistant Director of Transport Assessment and Modelling in Development Planning-TCCS-ACT Government. Ahmed as custodianship of the Strategic Canberra Transport Model (CSTM), he currently is leading and project managing one of the most enhancements applied to the CSTM.

Using Strategic Planning Methods for Evacuation Trip Distribution in Riverine Flood Disasters:  A Case Study in the Australian Capital Territory

The planning of evacuation operations for a riverine flood disaster is vital for minimising negative impacts on human lives.

This paper aims to develop a systematic method to model and plan evacuation trip generation and distribution for riverine floods. To achieve this aim, it adapts the transportation or Hitchcock problem, an operations research technique employed in conventional four-stage Canberra Strategic Transport Model (CSTM), and which is used to plan and model transport in non-emergency situations.

We focus on CSTM's first two stages, flood trip generation and flood trip distribution. We compare the adapted Hitchcock problem and the gravity model for flood trip distribution and proves that the adapted Hitchcock problem achieving better total and average evacuation times than the gravity model-based flood trip distribution.

Concentrating on pre-flood hazard planning, our evacuation trip distribution model considers two types of flood disaster data environments: certain environs, in which all decision variables are known, and uncertain environs, when approximate and uncertain decision variables are considered in the evacuation plans.

Bala Arumugham, Tauranga City Council - Find the best Toll Model!

Principal Transport Modeller | Tauranga City Council

Bala is currently a Principal Transport Modeller, leading and managing regional transport model updates for Tauranga City and Western Bay District on behalf of the Western Bay Modelling Partnership between local, regional, and national authority.

Find the best Toll Model!

Tolls and road pricing schemes are primarily used to recover capital and operating costs but also seen as a catalyst to reduce vehicle kilometre trips (VKT), to reduce emissions, to optimise network flow, to promote carpooling and to increase PT mode shift.

Tauranga currently has two of the three toll roads in New Zealand and increasingly over the past few years, we have undertaken several tolling and road pricing studies in Western Bay Sub-region for a wide range of regional and local assessment.

With these toll roads in operation for more than a decade, our transport models have also gone through several updates and improvements. 

Toll studies often are confidential to start with; classified as medium to high risk category type of modelling and financial/ economic appraisal project; and must be delivered in a very limited timeframe.

With new hybrid models and more data available, this paper discusses from a client perspective, the various model responses in applying static strategic model's vs dynamic hybrid models, and various demand responses at trip generation, distribution, mode choice and travel time of day choice. 

Some of the common questions while undertaking a toll modelling study are:  Is a more sophisticated model a better tool? How much to invest on a model update before option testing? i.e., defining fit for purpose; Need to avoid optimism bias, scrupulous honesty and objective analysis; Identifying project objectives and KPI;  Should we use a standard modelling methodology or a combination of models and other tools to support decision making?; How do we approach modelling for cordon/ congestion charging, tolling and dynamic road pricing?; and How good is the model forecast? 

This paper aims to discuss few common methodologies and steps applied on toll modelling from some of our recent regional and local projects, key results, differences and application areas.