Land Use and Congestion Management Strategies to Promote Urban Environmental Sustainability
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Reducing greenhouse gas emissions (GHG) is an important social goal to mitigate climate change. A common mitigation paradigm is to consider strategy ‘wedges’ that can be applied to different activities to achieve desired GHG reductions. In this dissertation, I consider a wide range of possible travel demand reduction and traffic congestion management strategies to reduce light-duty vehicle GHG emissions.
To estimate the cost savings associated with the implementation of various travel demand and traffic congestion management strategies, performance measures such as speed, delay, and travel time were assessed for each strategy. These performance measures were then combined with emission factors – amount of pollutants per speed interval – and monetary damage values of each pollutant in terms of mortality, morbidity and environmental damages – dollar per gram of pollutant – to estimate the external environmental cost savings resulting from the implemented strategy. Fuel and time cost savings were simply measured by incorporating the value of time and fuel.
Specifically, the external environmental cost of driving in the U.S. including congestion was estimated to be about $110 billion annually. Brownfield developments and LEED certified brownfield developments were assessed as land use and travel demand management strategies to reduce vehicular travel demand. Impacts of these residential developments on vehicle miles traveled (VMT) reduction and the resulting costs (cost of driving time, fuel, and external air pollution costs) were examined. Results show with minimal implementation cost incurred by transportation authorities (about 75-95% less than other VMT reduction measures), both brownfield residential developments and LEED certified brownfield residential developments can be beneficial travel demand strategies, assisting federal, state and local governments with their GHG emissions reduction goals. Compared with conventional developments, residential brownfield developments can reduce VMT and its consequential environmental costs by about 52 and 66 percent respectively. LEED certified residential brownfield developments can have an additional 1% to 12% VMT reduction and a 0.03% to 3.5% GHG reduction compared with conventional developments.
In addition to land use and travel demand management strategies, a number of supply congestion management measures were also assessed. Traffic signal timing and coordination is an effective congestion management strategy. However, not maintaining the timings regularly to assure they respond to vehicle volumes may result in 18 percent increase in the cost of fuel consumed, 13 percent in the cost of travel time and 11 percent in the external environmental costs annually.
Other supply management strategies assessed were cases of adaptive traffic control system and high occupancy toll (HOT) lanes. In comparison to one another, while adaptive traffic signal control system results in 7 to 12 percent external environmental cost saving, HOT lanes show zero external environmental cost savings. Driving patterns and speed profiles have significant impacts on the emission of the criteria air pollutants. In some cases, speed improvements resulting from the implementation of a congestion management measure may, in fact, result in the emission of additional criteria air pollutants, thus increasing the external environmental costs. Other interdependencies such as induced demand were also examined. Results show that induced demand from excess capacity resulting from an implementation of a supply congestion management strategy can be significant enough to reduce the benefits gained from the implemented measure in a short period of time.
In addition to analyzing travel demand management, land use changes and congestion management, strategies including fuel and vehicle options and low carbon and renewable power are briefly discussed in this work. I conclude that no one strategy will be sufficient to meet GHG emissions reduction goals to avoid climate change. However, many of these changes have positive combinatorial effects, so the best strategy is to pursue combinations of transportation GHG reduction strategies to meet reduction goals. Agencies need to broaden their agendas to incorporate such combinations in their planning.