Complex sentence: The first tunnel (started on August 20,1897 and completed on December 20,1900) had a problem with the smoke from the locomotives, because it was built with a 1.7% (1:58.8) gradient eastbound and too close to the ruling gradient.
Split into simpler sentences: The first tunnel began construction on August 20,1897 and was completed on December 20,1900. It had a problem with the smoke from the locomotives, because it was built with a 1.7% (1:58.8) gradient eastbound and too close to the ruling gradient.