Currently I walk both dogs at the same time with two separate leashes and do okay but in some situations it is a frustrating setup. Keno crosses back and forth on walks and it ends up with the lines tangled sometimes. To relieve this I have him on a shorter line than Kenzi so that he at least can't cross in front of her (and I have easier correction control since he wants to chase every leaf that moves and always wants to go on the opposite side of the tree). That works great when we walk the highway, but on trails they just have different paces. Surprisingly Keno is the one that is balls to the walls the whole walk, while kenzi starts out that way then lags the longer we go, then she'll get her second wind. I looked into the splitters but the trails are only wide enough to pass one at a time in many places. It could be that the way that I'm already doing it is my only option in this situation and trying some different training with keno is the key, but I figured I would ask. Kenzi is a good lead dog, not often distracted on walks, and she knows directional commands. I've done some work trying to teach Keno though haven't got him quite there yet.

I walk with a dog on each side of me, using a traffic lead, which is basically just a leash handle and the clip:
 

 
It allows me to have complete control over the 2 dogs, and it keeps them right next to me. Also, we can feel each other's energy and movements better than having it travel down a 6' leash or whatever. As soon as I move, they feel me and move with me. It's like we're working as 1 unit. It's nice. Also, if off leash dogs run up on us, I have a lot more control over my 2, and there is no getting tangled, etc.
 
I connect the traffic lead to a Softouch Concepts Harness (we have both the Sensation and the Sensible), which deters the pulling without putting pressure on their throat. If they pull, the harness goes across their chest, and they back off. Here's a pic:
 

 
With this setup, I have been in situations where we had to walk single file to get through tight squeezes, and we had no problem. Hope this helps.
 
Eventually we switched from walks to bikejoring, because it allowed them to run instead of just walk, and it takes a lot less time to get even more exercise (which is what they really needed!). Good luck.

I walk Ami and Archer on a contraption of 3 leashes - 2 connected to the third in Y formation. The tail of the Y is in my hand the each branch of the "Y" is attached to a dog. Works quite well, unless they are in play mode. Then they and their leashes conspire to kill me   Both dogs are tether-experienced and know how to dip their heads under the other dogs leash when they want to change sides.

I've been thinking about the traffic lead for Kenzi at car shows since there are other dogs that tend to get a little close. I guess my concern for using one on the long walks is will I be kicking the front dog in the butt when we are single file? I'm not sure how long they are. Most of the trails we walk are a foot wide for a mile or more.

I can't wait to get back to bikejoring. Truck has been broken for months so haven't been able to get bike anywhere. That would take care of Kenzi then I could just walk keno.

My only hesitation with adding that third line for the Y is that we walk a really busy road if we don't go to park and if we do go to park I think keno would end up wrapped around every tree in the land. Certain trails at my parents park though I think that would work great on. I will keep that in mind when we go visiting.

So the parts of the trail that are narrow and you'd be single-file...how long are they narrow for? A long ways? I know they makes leashes now that have a handle near the clip, as well as a normal leash that's 4' or 6'. So for narrow spaces, you can drop the short handle, and let one dog out in front a bit, and once you pass that narrow part, you can grab the handle again and keep one on each side of you under complete control. I used to rig this with a traffic lead and a normal leash, per hand/arm/dog, 2 dogs at a time. I was able to control them, but if I wanted them to explore, I could just drop the traffic lead and still have them on a 6' leash to sniff the ground and pee/poo, whatever. Now they make leashes all in one. Wish I had them back then! Here's a pic (you can see the wrist or regular handle at the top, and the handle close to the clip at the bottom):
 

counter wrote:

So the parts of the trail that are narrow and you'd be single-file...how long are they narrow for? A long ways? I know they makes leashes now that have ha handle near the clip, as well as a normal leash that's 4' or 6'. So for narrow spaces, you can drop the short handle, and let one dog out in front a bit, and once you pass that narrow part, you can grab the handle again and keep one on each side of you under complete control.

Excellent suggestion - the rok bungee leash that I have does just that - when the leash was given to me (Ami was a pouncer and kept landing me in the ditch, face first, so a friend got this for me), I thought the traffic lead was just a gimmick but thought the stretchy part would save my shoulder (and face  )...but I've used the traffic lead part on multiple occasions:  dense traffic in tight locations, when we're hiking and trail gets narrow (particularly in the gorges - he could knock hubby into the deep the way he crosses over whoever is in front), when people, children especially, want to pet him.  It also, inadvertently, taught Ami to "heel" without much work.  (Not that I use "heel" except in risky situations - I want Ami to be a dog and have, at least the illusion, when we walk, that he can go wherever his nose leads him)