Today, Saint Christopher is best known as the patron saint of travellers, and drivers in particular. He is often depicted on medallions and necklaces, for example, as a large man carrying a small boy on his shoulders, wading across a river and holding a staff to support them both.
It makes sense that Christopher obtained this particular description and title. After all, he helped countless travellers during his lifetime, saving them from injury or even drowning when they needed to cross the river. If anyone is going to be prayed for to give safe passage, Saint Christopher seems to be a good choice.