WASHINGTON, May 8 (Reuters) - The National Highway Traffic Safety Administration said Friday it is opening an investigation in a series of crashes of start-up Avride autonomous vehicles that raised questions about the competency of the vehicles.

NHTSA said the vehicles' performance may indicate inappropriate assertiveness and insufficient competence "and may also constitute traffic safety violations", and added some crashes resulted in property damage and one reported minor injury.

NHTSA noted that Avride is operating some of its AVs on the Uber UBER.N platform and has offered passenger service to the public since December in Dallas, where many of the crashes occurred.