Traffic assignment based on activity travel data: a case study

Abstract

Modelling traffic patterns has always been a ma- jor area of concern in transportation research. The four-step model has been the primary tool for fore- casting future demand of regional transportation services. The framework uses trips as an indepen- dent entity of analysis. This, however, leads to a number of serious limitations. Therefore, the orig- inal four-step models were replaced by tour-based systems. In a tour-based model, trips are explic- itly connected in tours, i.e. chains that start and end at the same home or work base. Neverthe- less, these models did not escape criticism either. It was claimed by several researchers that very lim- ited insight was o®ered into the relationship be- tween travel and non-travel aspects. This is where activity-based models come into play. The major idea behind activity-based models is that travel de- mand is derived from the activities that individu- als and households need or wish to perform. Travel should therefore be modelled within the context of the entire agenda, as a component of an activity scheduling decision. Because of the use of an activity-based model, a better traffic assignment module can be developed and as a result of this, the impact of transport on environment, traffic safety and health can be pre- dicted more accurately. A custom tool, PARROTS (PDA system for Activity Registration and Recording of Travel Scheduling) was developed to collect both activity data and GPS data. This tool is currently deployed in a survey that is carried out on 2500 households in Flanders. Two types of data are collected us- ing PARROTS: activity-travel diaries inputted by the respondents and location data logged by a GPS receiver. Activity-travel diaries and route information that are collected via GPS are linked and inves- tigated. By jointly investigating activity-travel di- aries and route choice information, a richer route- choice dataset is obtained. This enables investiga- tion of the route-choice process in the context of the activities and their attributes. Much research is going on both in the ¯elds of traffic demand modelling and traffic assignment. In the past, both research ¯elds have been developing independently. It is clear that by coupling traffic demand modelling and traffic assignment a power- ful tool can be obtained. The traditional approach towards the integration of traffic demand models and traffic assignment consists of aggregating travel demand in origin-destination matrices and subse- quently assigning these OD matrices to the trans- portation network. Activity-based models can pre- dict traffic demand by predicting activity-travel di- aries for the individuals within the studied popula- tion. The traffic demand can be derived from the requirement to travel from one activity location to the next. It is clear that aggregating the traffic de- mands resulting for all individuals in OD matrices yields an enormous loss of information. Indeed, it does seem reasonable to assume that on an indi- vidual level, the context of a trip plays a role in how an individual chooses a certain route. E.g. if the purpose of a trip is to go to work, the fastest route might be preferred. However, a route with a beautiful scenery might be preferred for leisure time trips.