May a passenger with a disability be required by transit personnel to show proof that an animal is a service animal?

Under Department of Transportation (DOT) Americans with Disabilities Act (ADA) regulations at 49 C.F.R. Section 37.167(d), transit providers are required to permit service animals to accompany individuals with disabilities in vehicles and facilities. Service animals are animals that are individually trained to perform tasks for people with disabilities, such as guiding people who are blind, alerting people who are deaf, pulling wheelchairs, alerting and protecting a person who is having a seizure, or performing other special tasks. A transit provider may ask if an animal is a service animal or ask what tasks the animal has been trained to perform, but cannot require special ID cards for the animal or ask about the person's disability. A service animal may not be excluded unless the animal is out of control and the animal's owner does not take effective action to control it or the animal poses a direct threat to the health or safety of others.