An Approach to Improve the Availability of a Traffic Light System

: Traffic Light System (TLS) is a standalone safety-critical infrastructure that is used to avert traffic congestion and accidents at a road intersection. It is pertinent that its service must be dependable because any failure could result to loss of lives or resources. The existing fail-safe TLS often experience downtime as a result of inevitable fault developed frequently by its Traffic Light Controller Unit (TLCU) due to harsh weather and other environmental factors exposed to on the roads. Hence, the need for a fault-tolerant TLS that will optimize TLS service delivery even at the event of a faulty TLCU initiated this work. In developing the fault-tolerant TLS, three TLCUs were interfaced using the concept of triple modular redundancy architecture. A disagreement detector was configured to test the viability of the primary TLCU using stationarity process. Markovian process was used to switch a faulty primary TLCU to a good one using majority voter mechanism. The fault-tolerant TLS and existing TLS were simulated using MATLAB R2015a. The performance of the fault-tolerant TLS was evaluated by comparing with that of existing TLS using availability as performance metric. The simulation results revealed that the fault-tolerant TLS yielded 99.9474% availability while simulation results of the existing TLS yielded 97.6199% availability. This work has therefore developed a fault-tolerant TLS that performed better than the existing fail-safe TLS.