Question: when did the speed limit change to 55 mph
[{'answer': '1974', 'provenance': [{'wikipedia_id': '6376043', 'title': 'National Maximum Speed Law', 'start_paragraph_id': 1, 'start_character': 101, 'end_paragraph_id': 1, 'end_character': 105, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '6376043', 'title': 'National Maximum Speed Law', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 287, 'bleu_score': 0.6871281838755551, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 10350195912763012050}, 'section': 'Section::::Abstract.'}]}]