Question: when did railroads become popular in the us
[{'answer': '1826', 'provenance': [{'wikipedia_id': '587997', 'title': 'History of rail transportation in the United States', 'start_paragraph_id': 10, 'start_character': 25, 'end_paragraph_id': 10, 'end_character': 29, 'bleu_score': 1.0, 'section': 'Section::::Chronological history.:Early period (1720–1825).\n'}]}, {'provenance': [{'wikipedia_id': '587997', 'title': 'History of rail transportation in the United States', 'start_paragraph_id': 2, 'start_character': 0, 'end_paragraph_id': 2, 'end_character': 326, 'bleu_score': 0.5793286095468101, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 3131441601948549298}, 'section': 'Section::::Abstract.'}]}]