John Douglas Hunt

Microsimulating urban systems

Abstract This paper presents a status report concerning on-going research and development work by a team of Canadian researchers to develop a microsimulation, agent-based, integrated model of urban land use and transportation. It describes in some detail the overall design and current status of the ILUTE (Integrated Land Use, Transportation, Environment) modelling system under development. The overall purpose of ILUTE is to simulate the evolution of an entire urban region over an extended period of time. Such a model is intended to replace conventional, aggregate, static models for the analysis of a broad range of transportation, housing and other urban policies. Agents being simulated in the model include individuals, households and establishments. The model operates on a “100% sample” (i.e., the entire population) of agents which, in the base case, are synthesized from more aggregate data such as census tables and which are then evolved over time by the model. A range of modelling methods are employed within the modelling system to represent individual agents’ behaviours, including simple state transition models, random utility choice models, rule-based “computational process” models, and hybrids of these approaches. A major emphasis within ILUTE is the development of microsimulation models of market demand-supply interactions, particularly within the residential and commercial real estate markets. In addition, travel demand is modelled explicitly as the outcome of a combination of household and individual decisions concerning the participation in out-of-home activities over the course of a day. Spatial entities in the model include buildings, residential dwelling units and commercial floorspace, as well as aggregate “spatial containers” such as traffic zones, census tracts or grid cells.

Current operational urban land-use-transport modelling frameworks: A review

Various alternative frameworks are available for modelling urban land‐use–transport interaction. This paper provides a detailed review of six of these frameworks that have been or are currently being used to develop operational models. The intention is to indicate what is the general nature of the current state of practice and what is now available for practical modelling work in the area. The intention is also to compare the current state of practice with what might be the ideal in various respects. The six frameworks reviewed (ITLUP, MEPLAN, TRANUS, MUSSA, NYMTC‐LUM and UrbanSim) are considered in terms of their representations of physical systems, decision‐makers and processes, along with various more general modelling and implementation issues. None matches the ideal as envisaged here in all respects. However, a wide range of policy considerations can be handled explicitly with what is available, and more recent developments show an encouraging trend towards expansion in the scope of what can be considered. Further strengthening of the behavioural basis and relaxation of some of the more restrictive assumptions would appear to be both appropriate and likely in the future.

The MEPLAN models of Bilbao, Leeds and Dortmund

A trio of closely related land‐use/transport interaction models was developed using Marcial Echenique & Partners’ software package MEPLAN. The models were for the cities of Bilbao, (Spain), Dortmund (West Germany) and Leeds (England). All were calibrated using data drawn from earlier studies. The three models were used to predict the effects (relative to a base case) of a common programme of land‐use and transport policies or scenarios. This paper explains briefly the theoretical basis of the MEPLAN package as applied to urban models such as these three; describes the types of policies that have been assessed; and presents some of the key results.

Theory and Application of an Integrated Land-Use and Transport Modelling Framework

Over twenty years of effort have gone into the development of a general framework for modelling land-use and transport interaction. This effort has been directed at integrating economic theory with operational planning methods in order to establish models that are advanced in theory, practical in operation, and useful in policymaking. The cornerstone of the resulting framework is that the location of activities and the economic linkages between them (in terms of goods, services or labour) are predicted by a spatially disaggregated input—output model with either conventional or more innovative forms. These economic linkages are converted into demands for transport that are assigned to modes and routes, taking account of congestion. Calculated measures of disutility in transport influence the location of activities through time. The entire system is based on a set of markets with ‘prices’ in money, time, or disutility units, making it possible to assess the effects of input policies or scenarios in economic and social terms as well as in physical units. This framework has been used to develop a wide range of models for different applications. The experience thus gained has helped identify a number of specific strengths and specific problem areas associated with the framework. The problem areas are, for the most part, related to practical difficulties that arise during calibration because of the complexity of the system. The various strengths of the framework make it most applicable in situations where there is a need for consistent land-use and transport predictions and evaluations, particularly in cases where there are relatively few observed data.

Specification and Estimation of Nested Logit Model of Home, Workplaces, and Commuter Mode Choices by Multiple-Worker Households

Household behavior in the selection of home location and the selection of workplace locations and commuting modes for employed members involves trade-offs among the attributes of the available alternatives for the different household members. A modified form of nested logit model representing this behavior has been developed and estimated using disaggregate revealed preference observations collected in Calgary, Alberta, Canada. Three categories of choice—choice of home location for the household, choice of workplace location for each worker in the household, and choice of mode for the trip to work for each worker in the household—are treated as a joint choice made by the household, allowing for differing numbers of workers in different households. A nesting structure that takes into account the greater similarity among mode alternatives is combined with a system for weighting, by age and gender, the contributions of different individual workers’ utilities to the total household utility. This leads to a nested logit model in which each household has its own nesting structure that is based on the age and gender of the household members. The utility function coefficients and weighting function parameters were estimated with full-information maximum likelihood by using purpose-built software. The resulting model extends consideration of household spatial behavior at the disaggregate level beyond the one-worker and sequential-conditional choice paradigms and provides various insights into the nature of this behavior.

Development of Microsimulation Activity-Based Model for San Francisco: Destination and Mode Choice Models

A tour-based microsimulation approach to modeling destination choice and mode choice of San Francisco residents is presented. These models were developed as part of an overall tour-based travel demand forecasting model (SF model) for the San Francisco County Transportation Authority to provide detailed forecasts of travel demand for various planning applications. The models described represent two of the nine primary components of the SF model. Both model components consist of multiple logit choice models and include both tour-level models (which refer to the primary activity of the tour) and trip-level models (other activities on the tour). A separate model was estimated for each tour purpose, including work, school, other, and work-based. The destination choice models combine the trip attraction and trip distribution components of the traditional four-step process and use a multinomial logit specification. The mode choice models utilize a nested logit formulation to capture the similarities among sets of similar modes. The two models are linked by incorporating the mode choice utility logsum in the destination choice models; the result is equivalent to a nested structure with a mode choice nest under destination choice. It is demonstrated that the microsimulation approach easily allows the inclusion of a number of key variables in destination and mode choice models that have a significant explanatory power compared with those in traditional models. It is also shown that this approach allows estimation of the effects of tour characteristics on the choice of destination and mode using widely available data and estimation procedures.

A nested logit model of parking location choice

This paper describes the estimation of a nested logit model of parking location choice using revealed preference data. These data concerned the behavior of drivers going to work in a central business district. The models nested structure acknowledges the relatively greater similarity among off-street and among on-street alternatives on their own. Each individual parking facility and surface lot is represented as a distinct off-street alternative. Areas of on-street parking constitute on-street alternatives. Special parking provided by employers is also represented separately. A variety of attributes other than money cost and separation from final destination were considered for the models utility functions. Both the proposed nested structure and the inclusion of measures representing various attributes other than money cost and separation from final destination were found to be appropriate.

FIRM LOCATION IN THE MEPLAN MODEL OF SACRAMENTO

MEPLAN land use and transportation-interaction models traditionally include models of business-location choice. The mechanisms in the model that allow for realistic aggregate assignment of firms to zones, and the resulting impact that firm location has on the entire modeling system, are described. The models use a form of logit function to allocate production activities to zones. Interdependencies in the Social Accounting Matrix, together with trip- and land-cost data and usage rates, generate a utility function for the attractiveness of purchasing a given sector’s output from a given zone. The alternative specific constants and the dispersion parameter are estimated in calibration, based primarily on cost data, trip-length distributions, and arrangement of activity in a calibration year. Results from a model of Sacramento show the various features and strengths of the model, while pointing out some weaknesses and potential pitfalls. The strengths include the realistic representation of current and continuing patterns, the close linkages between different industry and household types, and the market-based nature of the model. The weaknesses include the aggregate nature of the model and the possibility of difficulties in establishing realistic, alternative, specific constants.

Calibrating the Naples land-use and transport model

The calibration of a land-use and transport model of the Naples metropolitan area in Italy is described. The model is based on the MEPLAN general spatial interaction modelling framework that has arisen from initial efforts at The Martin Centre for Architectural and Urban Studies, University of Cambridge. A variety of parameter estimation methods were employed in the calibration effort. This included use of a process for identifying efficient parameter estimates in nested logit models, automated search routines for identifying values for the coefficients in multidimensional allocation formulae, cluster analysis procedures for developing zoning systems and category definitions, and various forms of log–linear multiple regression techniques. A complex manual procedure was developed whereby this set of methods was applied in a series of successive iterations. These iterations were designed to close in systematically on a model form and set of parameter values that would reproduce observed data that concerned the spatial distribution of different categories of employment and household, various economic interactions between these categories, and trips by person and vehicle on the transport network. The results demonstrate that the process can be used to slowly but surely establish an accurate model fit. This drawing together and practical application of the results of several areas of research has provided valuable experience and insight applicable to future such efforts.

Comparisons from Sacramento Model Test Bed

Three land use and transport interaction models were applied to the Sacramento, California, region by various teams of researchers. The results of these efforts were compared with each other and with the traditional transport demand model used by the regional government. The results of the modeling efforts are compared, with the focus being on how the design of the modeling frameworks and their application influenced the modeling results. A trend scenario was compared with three different policy scenarios: one that involved high-occupancy vehicle (HOV) lane construction, one that added beltway construction as well as HOV construction, and a third that involved light rail construction and limited pricing of automobile use. The results differ among the different models for the trend scenario, as well as for each model with respect to scenario-to-trend comparisons. The results show some of the limitations of aggregate models calibrated to cross-sectional data. The differences between the models provide important insight into how models should be calibrated and how their results should be used. Uncertainty in land use transport interaction models seems inevitable, and further research should investigate how such modeling frameworks should best be used to understand the influence of policy in the face of uncertain futures.