The 'horseback' group
These nouns refer to forms of transport or things that help you get about.
on crutches on foot on horseback on roller-blades on roller-skates on skis on stilts on the bus on the train on the tube
But it's cheaper for me to go on the bus.
Abraham padlocked the church gates and pedalled off on his bike.
The man on horseback looked down at her and frowned.
The following are used as normal count nouns:
bike boat bus coach moped motorbike plane scooter ship train tram