Growing trunk lines9 like the Erie, the Pennsylvania, and the Baltimore and Ohio completed construction of projects that had been started in the 1840s, and combinations of short lines provided new through routes.

• 伊利、宾夕法尼亚、巴尔的摩、俄亥俄等不断壮大的干线铁路公司完成了19世纪40年代就开始的建设工程，而短铁路线的会合提供了新的直达铁路线。