Effects of urban form on automobile dependency and energy consumption in Tehran residential regions

Climate change is threatening our planet and human settlements by its short and long time consequences. Globally, transport-related emissions of carbon dioxide are growing rapidly. The use of petroleum as a fossil fuel for transportation is the main source of carbon dioxide emissions. Statistics show that 22 percent of global CO2 emission occurs in transportation section and it is estimated that urban transport accounts for 8 to 13 percent of total emission in different countries. It is clear that any reduction in fossil fuel consumption in urban transport can help reduce total emission and improve the air quality in urban areas. Therefore, urban planners have considered different ways of energy usage reduction in the transportation section and have studied the effects of a wide range of factors on fuel consumption in urban transport over the recent years. Previous researchers have shown that urban form is a very important and effective factor that can affect energy consumption by 10 to 25 percent in urban transport. Based on reports by international organizations, Iran has the 7th ranking in the list of countries with the highest amount of carbon dioxide emissions.   The damage of carbon dioxide and other particles is 2.7 percent of Iran’s GNI. Considering the rapid growth of urbanization and subsequently the rapid growth of energy consumption in urban transport, the present article studies the effects of urban form on energy consumption and the amount of emissions of CO2 and other pollutants in urban areas of Iran. The focus area for the research is Tehran. International experiences have shown that socioeconomic factors like, age, sex, job, and the academic degree can affect the traffic behavior of urban residents. These factors have been applied as control variables to help the research to establish a clear relation between urban form and energy consumption. Like many different international researches, vehicle distance travelled (VDT) is applied as the main measure reflecting energy consumption in urban transportation section.  Regression analysis has been applied in the current research for determining the correlations between urban form factors and the VDT. For the purposes of the research, the socioeconomic and urban form factors for 300 individuals have been used from surveys like a sampling done by Tehran Comprehensive Transportation and Traffic Company (TCTTS) in 2005.  The sample volume used in the present research is approximately 195,000 individuals and 300 individuals were selected by applying systematic sampling method. Then, the collected data were divided base on the purpose of travel.  It should be noted that in Tehran Transportation Master Plan, travel purposes are defined as job, educational, service, leisure and other.  In the second step, travel distances for each person has been measured separately based on the purpose of travel. Preliminary investigations show that the share of job travels stands at 53 percent of total per capita distance travelled. It should be considered that vehicle distance travelled depends on vehicle choice of residents. For example, VDT for transit travels is considered as 0 in different researches over urban form and energy relations.  Travelled distance should be divided by the average of number of passengers in the specific vehicle type that is used for the travel.   The share of job-related travels of total VDT per capita is 63 percent based on measurement methods used in the present research. The impact of socioeconomic factors on traffic behavior and energy consumption is important and should be considered and measured alongside measuring the impacts of urban form.  By this, the evaluation of the exact effect of urban form on energy consumption in transport section is ensured. Socioeconomic factors have been applied as control variables in the analysis process of the research. TCTTS’s sampling that has been used as the main database for this research contains various socioeconomic characteristics of each person. Among them, job, age, sex, academic degree have been picked up as control variables in the model. Finally, the effects of urban form factors on Vehicle Distance Travelled (VDT) are separately measured for four travel purposes (educational, job, service, leisure and other). Eventually, it was established that the total effect of urban form factors on VDT per capita of all kind of travel purposes is more than 10 percent in Tehran metropolis. Results also show that  VDT per capita of job travels, which account for 63 percent of VDT per capita, can be described as a model of urban form factors but VDT of other three aims cannot be seen as a model of urban form.  According to the model, street accessibility, job accessibility and the area of living region have most effects on vehicle dependency of Tehran different regions residents.