Demand Side - Trip End Extraction Tool
Generated trips are the demand side entity for transportation planning. Land Use and Population are the dominant variable in the demand model. Travel demand is estimated for each TAZ. The source of data for land use, TAZ and population are maintained by different agencies. There are four look up tables derived for trip generation land uses, travel pattern, trip rates for each land use and populations.
Three basic modules are developed for:
- Extract trips ends for each TAZ
- Extract area for each TAZ
- Editing Tool
The trip ends for each TAZ is derived based on multiple linear regression model. The interface delivers two files for trip production and trip attraction in origin matrix (moxx1 ) and destination matrix (mdxx1 ) formats. (xx refer to matr ix numbers) These files are used as direct input to the emme/2 module 3.11. The land use areas are extracted with reference to each TAZ for secondary analysis.
In both the cases (trip ends and areas) the extraction of data can be even restricted to only one TAZ. This option improves the performance of the system. The editing tool is basically used to change land use code to test the preset scenarios e.g. evaluating impact of change in land use.
Desire Line Diagram
Using Enterprise GIS model, a tool is developed to analyse travel characteristics and generate desire line diagram. The desire lines diagram is schematic representation of travel desire between origin and destination. The diagram is represented with straight line connecting the trip origin and destination zones. Relative widths of the lines indicate the relative amount of travel desire between the zones. This tool generates thematic map of desire line with population information. Relative sizes of the circles indicate relative trip generating or attracting power of the zone represented in terms of total population.
In order to generate the desire line analysis maps, three data sets are used from the enterprise GIS database viz., population, travel demand and administrative boundaries. Population and administrative boundaries are maintained by Planning Council (formerly Census Statistical Organisation) and Planning Department respectively. Travel demand is derived from the emme/2 transportation-planning model.
Generally the travel demand is calibrated at TAZ level and maintained in emme/2 demand matrix format. Using emme2 matrix editor the travel demand is aggregated into desire spatial level (say municipality level in this case). The aggregated demand matrix is punched from the emme/2 databank. This aggregated demand file is used as an input to generate OD_Table in the INFO. In the OD_Table demand points are coded with municipality ids. SPIDER command is used with administrative boundary coverage and O-D Table in Arcplot module to generate OD line.
Similarly the population information is aggregated at municipal level and available as INFO Table. The INFO table used as lookup table with administrative boundary. The size of the circle is calculated relative the population data and defined by SPOTSIZE command.
TAZ Validation
TAZ is a basic geographic unit used for transportation planning and modeling. Temporal changes in the geographic extent of the TAZ with respect to trip generating variables have sequential impact in the travel demand forecasting. During 1994 initial TAZs for were derived from census blocks, which was delineated during 1987 census. Due to rapid change in the development and implementation of various sub-division projects, the census blocks are changed and re-delineated during 1997. TAZ validation task was undertaken to identify the consistency of the TAZs against the new census blocks. The data (land use, cadastral and census) used for the validation process are sourced from three different agencies. This task is carried out using multiple map overlay technique in Arc Info environment.
There are two basic criteria has been framed for identifying the errors in TAZs and as follows:
- TAZ should not bi-sect or cross the existing and/or proposed sub-division
- Homogeneity in terms of land use distribution
This process clearly identified that the TAZs exists around the sub urban of Doha area are greatly affected.
Benefits
Traditionally in transportation planning and modeling the tasks are carried out with a defined set of assumption on the currency of data used for analysis. The transportation planning and modeling team enjoyed the strength of enterprise GIS in Qatar during the development of national level transportation planning model. Some of the major benefits are:
- Received timely spatial and non-spatial data during development cycle of the model
- Minimised (in fact eliminated) lose of information during the data collection
- Conflicts of source and redundancy of data is minimised
- Frequency of data capturing and updating for the respective database is maximised.
- Minimised misestimating of trip generation, as the land use and population data are readily available via WAN during continuous case by case transportation impact studies due to land use change.
- Presented the transportation analysis reports in a more meaningful way with the help of supportive information available with another agencies.
Enterprise GIS Approach for India
Enterprise GIS approach has been proved most successful in State of Qatar. Implementation of the same concept in developing countries like India seems to be a myth. It is because of the size of the country. However, if we consider individual components of the approach and scale of implementation it would become a reality. The National Spatial Data Infrastructure (NSDI) Bill is the right example and it is the initial milestone in the Indian GIS industry’s approach towards enterprise GIS.
It could be more rational to consider the scale for initial deployment at metropolitan level. Some of the advantages for this consideration are;
- Urban planning problems are more in metropolitan areas
- Well defined area for implementation
- Short term development plans become more important than the long term master plans and thus planning authorities require timely flow of most reliable information
- IT infrastructure is readly available
- Agencies like Planning & Development Authority, Highway, Utilities & Infrastructure, Universities and Research institute etc., are centrally located
Conclusion
Qatar’s experience provides a model for governments and organisations in developing countries for implementing enterprise GIS, e.g. Jamaica, Vietnam. Organisational framework, standardisation, cooperation and data sharing are the more critical component of enterprise GIS. This paper also concludes that the fundamental aim of transportation planning and management i.e., providing safe, efficient and affordable transportation system to the society, can be effectively achieved with the implementation of enterprise GIS.
Disclaimer
The view expressed in this paper are only the author’s experience and with reference to other published sources and do not echo the governments, organisations or firms by whom the author has been retained.
Reference
- Balamohan N, Dr.Rashid-Al-Matwi, 1999, Travel Desire between Municipalities and Doha, ESRI Map Book Vol. 14, pp 109, ESRI, USA.
- Balamohan N, 1998, Data Exchange Protocol for Land Use Transportation Planning, Al-Khabar Vol.3, No.1, The Center for GIS, State of Qatar.
- Jerry C. Coiner, 1997, Transferability of the Qatar Enterprise GIS Model: Experience in Vietnam and Jamaica, GIS/GPS Conference’97, March 2-4, 1997, Doha, State of Qatar.