In an effort to increase the detectability of a motorcycle's brake signal, this study evaluated the effects of a modified stop lamp for motorcycles. With this modified stop lamp, both turn signals would flash simultaneously to supplement the regular stop lamp. The major concern with this design is the confusion between regular turn signals and the modified stop lamp with both turn signals flashing. Two experiments were conducted to evaluate this design using a PC based driving simulator equipped with three motorcycle taillight assemblies. The results suggest that the reaction time to a brake signal can be significantly reduced by 200 ms on average ( p<0.001) with a modified stop lamp, especially during the night when a taillight is on ( p<0.05). Although the normal use of a turn signal was affected by the use of a modified stop lamp by approximately 122 ms ( p<0.001), this adverse influence does not exist for a motorcycle that is straight ahead ( p<0.01). When regular turn signals are present, they do interfere with the use of a modified stop lamp by an average of 134 ms ( p<0.05). However, even with such interference, this design still requires a shorter reaction time than a conventional stop lamp by about 120 ms ( p<0.05). Overall, it can be concluded that even with the interference, the reaction time to modified stop lamps is still shorter than the reaction time to the conventional stop lamps in laboratory settings. Relevance to industry The results of this study benefit the tail lamp assembly design for motorcycles. The findings suggest that the modified brake lamps may be a promising device to improve the visibility of the motorcycle, and to provide easier identification for following motorists. However, the effect of this modified tail lamp on the original function of turn signals, as discussed in this article, should be considered in the design process.