The failure to provide seatbelts in a taxicab is a violation of Vehicle and Traffic Law § 383, and constitutes negligence as a matter of law. Where the injured plaintiff failed to wear an available seatbelt, that failure goes to damages, not liability. However, that is not the case where the vehicle owner did not provide seatbelts in the first place.
Grant v. AAIJ African Mkt. Corp., NY Slip Op 01823 (1st Dep't March 14, 2019)
Here is the decision.
