The performance of multiple-input-multiple-output (MIMO) systems is strongly affected by the properties of the channel matrices. In tunnels, despite the small angular spreads of the rays, it has already been shown that the average mutual information can be strongly enhanced using MIMO rather than single-input-single-output (SISO). However, limited information is available on the improvement of the bit error rate (BER), assuming a fixed throughput and transmitted power. In this letter, starting from measured transfer matrices in a straight arched tunnel, MIMO performances based on VBLAST or QSTBC algorithms are compared to those of a SISO link. Furthermore, the use of polarization diversity is also studied.