Okay, it doesn't help you much as a DM, because you still need to know why the short route is dangerous and probably have different encounter tables prepared for both routes. But if the travel comes up at the end of a session, you might quickly improv a travel triangle choice that a) your players can decide for next time and b) you can flesh out in preparation for whatever decision they might make.
Let me explore the idea a little. The easy route may involve taxes, social interaction with guards, or other less dangerous costs of its own, but usually its just longer, takes more time to traverse. The short route is generally the shortest distance between the two points, but the difficulties it entails may actually make it take longer to travel. But what are the various reasons the short route might be treacherous:
- A named monster: giant spider, giant, dragon.
- Terrain: quicksand, swamps, lava, caverns, reefs, whirlpools, canyons, mountains.
- Climate/Weather: tornado alley, desert, frozen pass, glacier, ice cave, lava.
- Humanoids: cannibals, headhunters, orcs, berserkers, raiders, slavers.
- Architecture: ruins, gates, crumbling mines, crumbling bridges.
- Magic: fairy woods, bermuda triangle, blighted lands, demon halls.
It seems like the short route should be at least a third shorter to be tempting at all and maybe half the distance/time to travel as the other. As far as knowledge, the party might know nothing, thus stumbling into the dangers of the enticingly shorter route. But the real drama seems to be when they have at least ominous rumors for the iffy route. Too much knowledge and the choice might become a sort of dry accounting, but knowing something called the Blood Saint lives along that path: "Hmm, we might want to take the longer way."
Which makes me think of issue 3) what is at stake behind the decision. In literature/movies time is almost always a scarce commodity that forces the protagonists to take the route they know is more risky. I think I'd rather set up the geography of these triangles in my sandbox somewhere and then wait for players to get themselves embroiled in plots that put that time pressure on themselves.
I wonder if there are other dramatic travel choice patterns I'm not thinking of.
note: it would probably make more sense to draw this choice as a semi-circle, but Travel Triangle is just catchier :)