With railways, a break-of-gauge occurs where a line of one gauge meets a line of a different gauge. Trains and rolling stock cannot run through without some form of conversion between gauges, and freight and passengers must otherwise be transhipped. A break-of-gauge adds delays, cost, and inconvenience.
Read more about Break-of-gauge: Inconvenience, Advantages, Overcoming A Break of Gauge, Minor Breaks of Gauge, Nominal Breaks of Gauge, Gauge Orphan, Gauge Outreach, Ideal Location, Equipment, Other Issues