In this paper, a discrete time sliding mode observer design for a linear time invariant system is considered. Continuous time sliding mode observer design is also discussed and summarized as a theorem for a direct implementation in the original state space realization of the given plant. Simulation of a linearized truck-semitrailer during a lane change maneuveur illustrates the approach. Results show the effectiveness and finite time convergence characteristics of the proposed discrete and continuous time sliding mode observers.