Abstract: A portable railroad attachment for a motor bicycle comprises a trolley unit for supporting the bicycle and having a pair of track wheels engageable with a first rail of the track and a third wheel engageable with the other rail. The trolley unit is detachably secured to the bicycle frame by a swivel coupling which provides a pivotal support about which the bicycle is pivoted under the weight of a rider to bring the driven wheel of the bicycle into tractional engagement with the first track rail.