What's the longest straight path in Emerald that's also free of Pokemon? The path I ride along for hatching eggs passes through Route 118, Mauville City, Route 117 to Verdanturf Town. Is there a path in the game that's longer than that?

Nope, that's the longest path in the game. It's also conveniently right next to a) the pokemon breeder, on Route 117, and b) the Happiness checker person, in Verdanturf.

Technically, there are "infinite" paths which you can take, andnot encounter pokemon. These paths can be created by trying to do things where a particular skill/item/ability/etc are required, but you dont use/have the skill/item/ability/etc. Examples of this would be trying to go up a Waterfall without the pokemon actually using Waterfall, or trying to go up a dirt slope while walking or on an Acro Bike. I use this trick when I get lazy after EV training and throw pokemon into the daycare to level them up higher, or have Friendship-evolution pokemon I need to evolve. In fact, I use the following steps:

1. Put desired pokemon/egg into daycare/party.

2. Go to the Trainer Hill place north of Mauville.

3. Select "Variety Tag Match"

4. Go up the stairs and find the arrow pointing up ^. If you walk on it, it should send you backwards.

5. Heres where it gets slightly tricky. Find a couple of small, but heavy objects. 3 - 5 pounds works well. Place one of them so that it pushes down the Down arrow of the d-pad, and the other object so it presses down the B button. This should make your character run down onto the arrow, and be pushed back up.

6. Put game in a location where it wont get jostled or bumped into.

7. Do whatever you want for however long you feel. Personally, I do this at night and thus go to bed.

8. Return and check the game. If you character is still running, good. If not, I cant make any promises =/

9. Save if desired, and go to daycare to check on pokes.

10. Rejoice.

A note of caution though: I dont advise trying this trick on a regular GBA. This can drain a lot of battery life, which could make the GBA turn off and lose the levels gained. Only do this on a GBA SP or a DS, with the backlight on the lowest setting, and with th SP/DS plugged in to its recharger.

This trick mayseem complicated, but it helps a lot for happinessand raising weaker pokes. I think the highest level gain Ive gotten was when a lvl 2 Poocheyena grew to lvl 40-something.

I did the same thing with my shuckle, while I was out of town I set up the gameboy with a pair of visegrips to hold the up button down at the dirt slope north or mauville. I put him in at lv23 and got him out at lv100!!!

Aye, that's what I do too, but I don't really breed Pokemon often. blaziken234's method is useful and frees you to do other tasks, but it doesn't appeal to me. But do whatever floats your boat

i build a setup that pushed up and B out of legos i had lying around, it works extremely well and i can even shake it and it dosent move, right now im lvling my sceptile and blaziken from lvl 70 to lvl 100 for BT

That dirt slope trick doesn't work for me. Is there a problem?

You Have to have the Acro bike and when you go to dirt slopes it should make you slide down again then find some way to keep the Up button down(with something 2-4 pounds but small like blaziken234 said) then youre set

i tried to talk my mum into holding down the button for this, she refused. the vicegrips are most likley the best option. i'd think you'd only need the up button, 'B' on an acro bike could send you hopping...

On emerald It Don't seem to work for me, I made a test, I took two Pokemon that were EXACTLY the same (I cloned it).
At my Sapphire it went up from 5 to 86 in one night.
At my Emerald it went up from 5 to 18 in the same time.