This report presents three case studies that illustrate how geographic information systems (GIS) have been used to implement the Federal Highway Administration's (FHWA) Planning and Environment Linkages (PEL) approach. The PEL approach provides information and tools to help agencies integrate consideration of environmental factors into transportation planning. PEL represents an approach to transportation decision-making that considers environmental, community, and economic goals early in the planning stage and carries them through project development, design, and construction. This can lead to a seamless decision-making process that minimizes duplication of effort, promotes environmental stewardship, and reduces delays in project implementation. This report identifies some effective uses of GIS to support the goals of PEL and will be helpful to transportation and resource agencies considering applying GIS to implement PEL.