Concerns have been raised that PPPs may not sufficiently safeguard the environment. Some say, for example, that PPPs may allow private entities to choose less costly and less environmentally friendly construction and maintenance methods; encourage higher traffic rates-yielding higher emissions-to maximize revenues; or use private financing to avoid the National Environmental Policy Act (NEPA) requirements for federally funded projects. To address this, PPP contracts may include enforceable environmental performance standards; environmental studies and mitigation also have been integrated into PPP processes.74