Complex sentence: In 1901, gauntlet track was installed through Oxford Tunnel, providing more overhead and sideways clearance as rail cars and locomotives grew in size, but the newly overlapping tracks decreased operating capacity through the tunnel, and the bottleneck worsened.
Split into simpler sentences: In 1901, gauntlet track was installed through Oxford Tunnel, providing more overhead and sideways clearance as rail cars and locomotives grew in size. But the newly overlapping tracks decreased operating capacity through the tunnel, and the bottleneck worsened.