This paper proposes a new joint rate allocation scheme for statistical multiplexing of multiprogram video coding in broadcast systems. The scheme is based on a scalable video coding (SVC) platform that does not require computationally expensive re-encoding or transcoding to adjust the bit-rate of each video signal. A new complexity measure that incorporates the characteristics of Human Visual System (HVS) is first introduced in the look-ahead approach. The bit-rate for base layer coding is thus more efficiently distributed among videos according to their relative complexities. A piecewise linear model is used to estimate the rate-distortion relationship in SVC enhancement layers. Based on the model, we develop a joint rate allocation scheme to dynamically allocate the available bandwidth by taking into consideration both inter-program fairness and intra-program smoothness constraints. Experiments have been carried out to compare the performance of existing methods with our proposed scheme. Results demonstrate that the proposed scheme achieves a fine balance in picture quality across all statistical multiplexed videos as well as within each video.