- Americans with Disabilities Act (ADA) paratransit systems are dial-a-ride services that provide public transportation to disabled customers. In large metropolitan areas, these services might use zoning strategies to simplify their management. The objective of this paper is toprovide a more in-depth evaluation and comparison between centralized and decentralized zoning strategies. This is achieved by developing a simulation model to evaluate the effects of zoning strategies on the productivity and quality of service for the particular ADA paratransit service, using actual demand data from the city of Houston. Four decentralized zoning strategies are compared with a centralized no-zoning strategy. Higher degrees of decentralization degrade the operational efficiency in terms of larger fleet size because the causative empty trip kilometers are greater. The intrazonal trip percentages of demand and productivity are positively correlated. 2013 American Society of Civil Engineers.