NASA has been involved in developing advanced automation systems for improving the efficiency of air-traffic operations, reducing controller workload and enhancing the safety in the national airspace system. In the past decade there has been emphasis on designing environmentally friendly operations that reduce fuel consumption, emission and noise as well. The objective of the proposed research is to develop a framework suitable for the design and analysis of 4D trajectories for terminal and transitional airspaces targeted for far-term implementation. The novel aspect of the proposed research addresses efficiency, throughput, and safety all in a combined and integrated manner. Advanced optimization algorithms will be used in the design of these trajectories. Research will also establish the feasibility of tracking these trajectories using 4D guidance algorithms. Analysis will be done to study the tradeoff between fuel consumption and the time of arrival. Phase I research will demonstrate the 4D trajectory synthesis and 4D guidance algorithm using realistic commercial aviation aircraft models. Phase II research will develop the tools to a level that can be used by NASA researchers in the development of NextGen concepts.