Power dissipation in long interconnects and increasing wire temperatures due to (self) Joule heating are becoming important issues to address in nanometer-scale technologies. While many low-power bus encoding schemes have been proposed, no encoding techniques exist for explicitly reducing temperatures in high-speed on-chip signal buses. In this work, we propose: (1) an interconnect/wire signaling and layout optimization that considers self and inter-wire coupling activities and is tailored to data traffic characteristics; (2) an integer linear programming (ILP) technique to optimize bus energy and; (3) a novel methodology to add thermal constraints to this ILP optimization to reduce not only average but also peak wire temperatures. Our contributions enable a designer to efficiently explore the hottest wire temperature and total bus dynamic energy trade-off space. One such trade-off point yielded a thermally-constrained, energy-optimal encoding scheme that reduced wire temperatures by up to 12.26 degC (12.96 degC) for data (instruction) bus and significant average energy savings of 14.24% (16.17%) for data (instruction) bus. These results are still much better than energy reductions obtained by previous work.