Tehran is the capital of Iran and is one of the largest cities in the world. With its history of earthquakes, high population density, and a population of over 8.5 million, it must be prepared to cope with disaster. This article introduces a new method for estimating the reliability of a roadway network that considers the physical characteristics of the road and link capacity degradation. The proposed method was applied to a real road network and the connectivity reliability of the city was calculated. The proposed technique for computing connectivity reliability is sensitive to the characteristics of the road and adjacent buildings. The results indicate that northern Tehran, with a low population density and newer buildings and highway network, shows higher reliability for origin and destination trips than other regions. This region has a higher probability of connectedness to other regions after a disaster. The weakest area of the network lies in the southern and central regions with older buildings and no highway network. These regions show low connectivity reliability and high population density. These results provide useful insights into the vulnerability of the Tehran network in response to a major earthquake.