Over the last two decades, cities in the Middle East have witnessed significant growth in economic development, resulting in population growth and higher levels of employment which, in turn, resulted in increased daily trips on limited transport infrastructure.
To cope with the fast pace of development, the concerned authorities accelerated transport infrastructure expansion, but its pace has not matched the pace of development growth, mainly due to the time required to plan and implement transport infrastructure. As a result, unacceptable level of traffic congestion is present in these fast-developing cities, resulting in decreased levels of urban mobility.
To aid the development of appropriate transport infrastructure, the authorities began the development of comprehensive multi-modal transportation models to assist planners and engineers in making informed decisions.
In the United Arab Emirates (UAE), Abu Dhabi and Dubai have already developed comprehensive multi-modal models using advanced techniques and modelling software. The Emirate of Sharjah has just completed the development of a similar model, and the Emirates of Ras Al Khaimah and Ajman are currently in the process of developing such models.
Although these models are useful in predicting future travel demand, they are strategic in nature and not appropriate for addressing existing traffic and urban mobility issues. Clearly, there is a need to focus on current and short term traffic related issues with a view of maintaining acceptable level of urban mobility.
Furthermore, Dubai is the main hub in the UAE and there is significant amount of daily traffic between Dubai and other Emirates, particularly Sharjah, Ajman and Ras Al Khaimah. Clearly, a UAE-wide strategic transport model would be most useful for evaluating traffic conditions on major routes within each Emirate, and planning cross-Emirates travel corridors. The Emirate-wide strategic transport model would then be complemented by an Emirate-wide traffic operational model to address existing and short-term traffic issues with a view to improve accessibility and urban mobility.
The development of comprehensive multi-modal transport models has become a trend in the Middle East. These strategic models are not suitable for addressing existing traffic congestion which has led to reduced urban mobility
Typically, demand forecasting models include the traditional four stages of trip generation, trip distribution, modal split and trip assignment. However, details within each stage are structured with a view of representing local conditions and reproducing the travel behaviour of various population groups for different journey purposes. Furthermore, a key feature of the model is the relationship between the base conditions and future projections. Internationally, it is accepted that the validated base model parameters would be applicable to future travel conditions. This assumption is probably reasonable in developed countries where there is little change in land use patterns, population mix and travel conditions between the base and future years.
As such, models in developed countries are incremental, pivoting around the base conditions. However, in developing countries and in particular in the Middle East, the patterns of land use and daily trips are continuously changing and, in most cases, completely different between the base and future years. This is the main reason for existing models in the Middle East being absolute models with no direct relationship between base and future year models, other than model parameters.
However, this may cast doubt on the reliability and validity of forecast year projections. Given the extensive efforts in validation of the base year model, it would be useful to develop an approach that establishes a relationship between the base and future year values with a view of increasing the reliability of future year model output. This would, in effect, be combining the incremental and absolute modelling approach.
Model validation is an important aspect of the model development process, checking the accuracy of model estimation. Extensive data and rigorous criteria are used for validating different areas of the model. Generally, guidelines and standards from the British DMRB Manual are used for validation of these demand forecasting models.
However, these rigorous validation criteria would be applicable and achievable in stable conditions such as those in developed conditions, but more difficult to achieve under continuously changing conditions such as those in the Middle East.
Furthermore, it is not clear that, even if model validation based on rigorous criteria could be achieved, how valuable this would be as regards the reliability and accuracy of model forecasts in an absolute model structure where there is little relationship between base and future year models. Clearly, the international guidelines and criteria are important for checking the validity of model estimation, but consideration should be given to local conditions and, where possible, the criteria should be revised to reflect local conditions.
Typically, demand forecasting models are strategic in nature and applied to forecast changes in travel pattern between travel modes, along key transport corridors and across the study area, under a given scenario. The validation of these models is also at strategic level, and model output at local area level is therefore not necessarily accurate.
However, strategic models in the Middle East are being used for local area studies, including traffic impact studies. Also, these models are occasionally being applied for assessing traffic management schemes that should be done using an appropriate operational modelling tool. There is therefore a need to develop supporting city-wide operational modelling tools to complement the existing strategic models.
Generally, demand forecasting models are updated every ten years and usually coincide with general census. However, in the Middle East, where there is a rapid and continuous change in land use development and trip patterns, there may be a need to update the model more regularly and not later than every five years. Ideally, every five years, the model should be re-based and calibrated and validated to reflect the changes in demand and supply. As this would require an extensive and expensive data collection programme, there is a need to develop an approach for continuous and targeted data collection programme using smart technology.
The development of comprehensive multi-modal transport models has become a trend in the Middle East, even in cities where there is no public transport, or at best a few bus routes serving a relatively small population. These strategic models are not suitable for addressing existing traffic congestion, which has led to reduced urban mobility, or for improving general accessibility levels.
There is a need to develop operational traffic models to study and develop appropriate mitigation measures with a view of addressing existing traffic issues and improving urban mobility.
The level of complexity, details, development and application of a transport model should be aligned to local travel conditions. There should also be a balance between efforts and expenditure on base year model development and forecasting in an absolute model, unless elements of the base year model other than parameters are used.
Reza Mohammadi is Director of RMC, Dubai
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