Maintenance deferment has huge implication in vehicle operation and on national economy. Delayed maintenance ultimately results in reconstruction which will be very expensive for a country like Ethiopia which is promisingly developing at the moment. In this regard, the adverse impact of maintenance deferment is the focus of this research. This paper characterizes poor maintenance in terms of delayed application of the required maintenance activities and in accurate forecasting of traffic flow. For studying these effects, a principal arterial road along the east-west corridor of Addis Ababa was chosen. The road network starts from Megenagna passes through Meskel Square and terminates at Torhayloch (8.2Km length). The research uses HDM-4 to measure the impact quantitatively. The model integrates road network conditions, vehicle characteristics and maintenance programs and finally generates a summary of the economic indicators. When maintenance neglect continues, it will not only reduce service levels and accessibility but also hugely increase the whole lifetime cost of the transport infrastructure. This eventually incurs negative impact in overall economic growth of the country.