There are several routes that connect the different cities in a region, which is the main highway for trainers. There are Pokemon Centers and PokeMarts in each city which provide supplies and a place to rest and heal Pokemon. There is usually a smattering of trainers on each route, so even if something did happen, a trainer could easily find help.

Not to mention trainers are not allowed to go out into the wild without at least one Pokemon. They serve as protection as well.

[Yeah, Lance's world is probably a utopia compared to Luke's.]