A proposal model for residential density and distribution of activity compatible with TOD (Case study: District 12 of Tehran)

Land-use and development density decisions have always been amongst the most controversial issues in urban planning. Various approaches have been proposed to deal with these decisions. However, these approaches have been mainly theoretical rather than practical. Transit Oriented Development (TOD) is amongst the most recent approaches to urban planning and, consequently, land-use and development density decision-making. TOD has been defined as “a compact, mixed-use, community, centered around a transit station that, by design, invites residents, workers and shoppers to drive their cars less and ride mass transit more.” This paper aims at proposing a mathematical model for land-use and development density decisions based on the principles of TOD. TOD is generally considered to have three dimensions: design, density and diversity. Design needs to be prepared according to specific conditions and circumstances of each particular station area. On the other hand, planning for development density and diversity needs to be developed from a holistic viewpoint, regarding different macro-scale objectives and constraints. In this paper, the problem of development density and diversity optimization based on the principles of TOD is modeled as a mathematical programming problem with multiple objectives. The first objective is to maximize development density in station areas, and the second objective is to minimize the difference between each station’s ratio of job-housing balance and its ideal value (ratio of employed people to the number of residential units) in each TOD area. Several constraints related to the objectives of Tehran master plan have also been incorporated into the model. The resultant nonlinear model was transformed into a Multiple Objective Linear Programming (MOLP) problem using simple mathematical transformations. Then, using AUGMented Epsilon CONstraint (AUGMECON) technique, it was transformed into a single objective Mixed Integer Linear Programming (MILP) problem. Finally, the model was applied to a real case study in the 12th District of Tehran metropolitan area and the results were thoroughly analyzed.
Statistical analysis of the results shows that the elasticity of diversity to development density is -1.017. In other words, 1% improvement in diversity leads to a 1.017% decrease in the development density index. Optimal trade-off between these objectives depends on (1) their relative impact on car ownership ratio, vehicle-miles travelled and similar criteria, (2) particular micro-scale issues of each station area as well as the goals and strategies of the municipality for each station area. Previous studies show that land-use diversity has a higher impact on the aforementioned criteria than development density. However, these results depend highly on urban development, urban transportation patterns and the behaviour of citizens. Hence, proper decision-making needs a separate study on the aforementioned impacts on travel behaviour of the citizens in the context of Tehran.
Furthermore, the Pareto solutions of the proposed model provide a set of alternative development policies and enable the policy-makers to select among them based on their specific conditions and limitations. The proposed model results can be applied to future urban development plans.