In Mumai, the 13-year-old Dindoshi flyover was supposed to have been sturdy for 50 years. But by 13 years itself, cracks and damage show the sorry state of one of the busiest bridges in western suburb. The Maharashtra State Road Development Corporation (MSRDC) said that as a thumb rule, a flyover is constructed with a minimum lifespan of 50 years while the maximum can even cross 100 years.    Other flyovers in Mumbai, including Parel and Kemps Corner flyovers, have crossed at least two to three decades of service without any major structural problems.    Mumbai Metro rail's viaduct has been engineered to serve for 125 years, whereas the Delhi metro rail’s life span is 120 years.    The Ultadanga flyover that collapsed in March this year in Kolkata had a lifespan of 50 years. Built in 2011, the bridge collapsed in two years. Later, the civic body there conducted an audit of all bridges in Kolkata.