A fleet modernization program is an ambitious policy requiring major investment for it to be implemented at the national level. To maximize the benefits of the program, policies ranging from periodic vehicle registration to low emission zones would be needed. The program could begin with a subset of the proposed policies implemented in major urban areas, where similar vehicle emission reduction programs already are being considered and later could be scaled up to the national level. The objectives of a heavy-duty fleet modernization program are threefold: (1) to rapidly reduce in-use emissions, (2) to accelerate the transition to newer emission standards and (2) to closely track and monitor the in-use fleet. Such a fleet modernization program would not only achieve short-term emission reductions from retiring vehicles, but also would ensure long-term emission reductions by promoting the use of the cleanest new vehicles available.