A general framework for classification of road traffic models is presented below.  This two-dimensional framework considers the nature and level of detail offered by a traffic model in handling road geometry and traffic elements.  The focus is on the movement of vehicle traffic (see the note below about different traffic modes). 

Software developers and users are invited to submit comments on this framework, and request inclusion of their models in appropriate categories.

Contrasting models as macroscopic vs microsimulation, deterministic vs microsimulation, empirical vs theoretical, empirical vs analytical, etc are not valid ways of qualifying models.  Models never fall into clear-cut categories, but there is a spectrum (continuum) of models.  The framework presented here may be helpful to understand that analytical models or simulation models can be microscopic or macroscopic (and in between). 

US Highway Capacity Manual Edition 6, Chapter 6 presents a useful discussion on models. 

For the purpose of the framework presented below, the analytical models are defined as those that use direct mathematical computations to determine system states, and simulation models as those that use various rules (mostly in the form of mathematical equations) for movement of vehicles in a system (individually or in platoons).  The HCM models are analytical.  HCM Chapter 31 states that "The HCM methods represent traffic flows with variables that reflect flow dynamics.  These methods stop short of representing the movements of individual vehicles.  The intent is to employ calculations that can be done by hand, using a set of worksheets, or by computer ...". 

In the framework presented here,

(i) a simulation model can be microscopic, macroscopic or mesoscopic;

(ii) an analytical model can be microscopic, macroscopic or mesoscopic;

(iii) a simulation model can be deterministic or stochastic.

Notes

Analytical traffic models usually incorporate stochastic elements (e.g. overflow queue models for traffic at intersections) although each application of the model may produce the same outcome (deterministic).  The distinction "Stochastic vs Deterministic" does not necessarily imply model quality since parameters of traffic elements at every level of detail (individual vehicle. platoon, traffic flow, etc) can be randomised.

Contrasting models as "Empirical vs Theoretical" represents a simplistic view since most models have basis in traffic behaviour theory and are empirical at the same time. However, the term "empirical model" is usually used to mean "based on statistical analysis of field data without any direct basis in traffic theory".  

The framework presented here is limited to vehicle traffic.  The issues of different vehicle types (movement classes) and driver types, and the size of the area modelled (single intersection, arterial, network, etc) are further considerations in this context. 

Different modes of traffic (pedestrians, cyclists, public transport) could be added as a third dimension to this framework, each with its own special considerations.  For example, for pedestrians, drive cycles are not applicable, and pathways rather than lanes would be relevant. 

A general framework for road traffic models

Traffic
Elements
ROAD GEOMETRY ELEMENTS
 Approaches
(all Lanes Aggregated)
Lane group
(or 'links)
Lanes
(or lane segments)
Individual vehicles NA Micro-simulation
Platoons Macro-simulation Meso-simulation
Drive cycles NA Micro-simulation
Traffic flows Macro-analytical Meso-analytical Micro-analytical
Speed - flow models Macro-analytical NA

 

(1) Drive cycle may be defined as the vehicle speed-time trace consisting of acceleration, deceleration, cruise and idling elements.

(2) Lane Group is a set of lanes with one or two shared lanes (e.g. Lane 1: Left-Turn and Through, Lane 2: Through) or a set of exclusive turn lanes (e.g. a single Right-Turn lane).  

Traffic modeling software packages according to the above framework

  Level of traffic and road geometry detail
Typemacroscopicmesoscopicmicroscopic
  *e.g. CUBE, EMME, VISUM
Simulation

LINSIG
SATURN
SIDRA INTERSECTION
SYNCHRO(?)
TRANSYT (UK)
TRANSYT7F (USA)

CONTRAM

AIMSUN
CORSIM
CUBE DYNASIM
DYNAMEQ
PARAMICS
SIDRA TRIP
SIMTRAFFIC
TRANSMODELER
VISSIM

Analytical ARCADY
*Transport
Planning
Packages
HCS
*Transport
Planning
Packages
SIDRA INTERSECTION

Traffic modeling software packages in each group are listed in alphabetical order.  Although it is simplistic to place software packages into separate boxes (since different aspects of a package may employ different levels of analysis), the above table is intended to indicate the dominant model characteristic in each package.  Links are provided to SIDRA SOLUTIONS software supported.  SIDRA INTERSECTION is placed in the "Macroscopic - Simulation" category due to the use of lane-based second-by-second platoon patterns for signalised networks, and placed in the "Microscopic -Analytical " category for detailed lane-by lane model used for intersections and networks. SIDRA TRIP is a single vehicle simulation model.

Rahmi Akçelik
First published: 30 August 2004
Last Revised: 24 August 2017


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