A few tips to make your life easier:

• Never use dirt roads and try to always take urban roads as the first unlock. Urbans aren't that expensive but the speed is way higher, which is essential when it comes to intersections. Also, try to unlock urban roads speed upgrade in mid-game
  
• When you create highways (which are two parallel one-way roads, where the right one goes forward), leave a gap between the roads. One tile is enough, but you may leave two or even more. Just don't overdo it, because the PF PathFinder can mess up with pathing and don't use preferred way at all
  
• Always use mirrored warehouses if you don't have a solid reason to use a not-mirrored one. Mirrored warehouses have an entrance at its right side, and an exit at the left, so you will thank yourself in late-game when the traffic becomes crazy if you play with left-hand driving stowp being bri'ish lad use the default warehouse
  
• In one 2019 discussion the developer stated that for each warehouse you shouldn't have more related to this warehouse producers and consumers than half of its radius. If it is 30, don't place more than 15 gatherers, farms and factories in its radius. Or manually send their production to other buildings But I'm here to explain how to avoid that limitation
  
• If you concentrate at food production, a significant part of your traffic will be the water distribution, so unlock irrigation towers when you have enough money
  
• Always look for a way to optimize your production chains. If you want to make dough, place flour factories nearby and manually send their production to each dough factory. Combine it with interchanges, and your network will be fine

First things first, let's talk about WLM~ wait, hol' up... Let's talk about WL&M conception. What kind of roads do we have in the game? Default urban roads (2 lanes / 2 ways), one-way roads (2 lanes / 1 way) – and looks like that's it, right? Actually, there is one more tool that you can create – 1 lane / 1 way road

We place down a piece of urban road and plop a tile or two of one-way road in middle of it, preferably away from intersections, and voila! – the opposite lane is disabled. That would come in handy when you want one-way road, but you also don't want trucks to take left line for a turn

Speaking of left lines, there is the rule of thumb which was told by developer: trucks take left lane at one-way road if they will turn left at the next intersection
                    We can separate traffic by lanes making them turn left at the end of the way

But what can we do, if there is a right-forward intersection, and all the trucks use the right lane because there are no left turns, when we would like to have the right lane for turning right and the left lane for moving forward? We make the trucks turn left and then right again, which means they still go forward, but by the preffered lane
                     Basically, we make a left-forward intersection instead of forward-right one

Why do we need this? Because trucks won't slow down before intersection if they have dedicated lanes that don't cross. So if we have right lane for right turns and left lane for direct path, the flow never stops

Now take a look at the best way to merge one-lane road with urban

Remember, T-intersections are your best friends, because with this setup, each way on urban road has its own lane on one-way road to go. There is no conflict – traffic flows. The correct way to build this is to place urban road between one-way road pieces and connect those pieces with an one-way segment overlapping urban road


I have no idea why, but sometimes when I merge it any different way, something goes wrong and trucks stop before making turn, even though they shouldn't.


                        A fun fact about dirt roads – they have the same priority as urban road.
            So we can't manipulate the traffic using them. That's a shame. Forget about dirt roads

Before we proceed to interchanges let's talk about why do we need them at all.
The first thing you shall remember – avoid placing intersections in nearby tiles like shown in the picture

The game sees them as one intersection and this is bad because there can be no more but one truck at intersection in the same time

Look at the picture: we have two different routes where trucks are aimlessly carrying water from one warehouse to another, and a T-intersection near each warehouse
As I mentioned above, trucks won't stop on them because they have dedicated turn lanes which don't intersect. Now we plop a couple of intersections in the middle of the route
Trucks are stopping now, but it doesn't really matter – the network balanced itself in a moment. Now, what if we move the right intersection a tile to left?..
Yeah, now it really slows down. And if we had any more traffic from these additional ways, we'd have a nice traffic jam already. And if it is a highway intersection, which has 2x2 size, it's getting even worse.

But you can create intersections in nearby diagonal tiles, because there is a gap between them

When the game tries to find a route to from A to B, it doesn't care about how many intersections the way has, it just tries to pick the shortest one actually, I don't know exactly how the hell the PF is looking for the best way, but I will tell you about this all later

By the way, even if an intersection takes up only single tile, trucks still will slow down a bit. But if the trucks have higher speed, they will pass by the intersection faster, and other trucks will wait less time. So use urban roads and upgrade them if required. And if you get something like a blizzard event (which will cut trucks speed by 50%), you can get traffic problems in that spots, where you've never expected

But what is an intersection at its pure form? Intersection is a tile where multiple routs cross. Let's look at the picture: we want to turn right – no problem, trucks even won't stop before this intersection because of dedicated lanes


Okey, now let's go forward
                                                Does it sparkle with all the routs? Sunshine!

Although trucks now will stop before passing forward (one truck at intersection rule), there are still no conflicts yet. Now we have to go left – and now we are conflicting with the opposite lane


That's why we need interchanges, which main goal is to dispose all the left-hand turn conflicts or minimize their count.

The simplest interchange you can create is a lane merge
If the traffic isn't heavy and the trucks go only to and from one direction, removing left-hand turn conflict with a ramp should be enough. But remember, this is the simplest case...


There are two types of interchanges: Service and System.

Service interchanges connect a highway to local streets or arterial roads. When you connect sand collectors to a warehouse, for example. The idea of service interchanges is that we don't really care about the traffic on local road because there is only a couple of trucks every 15 or 30 days and we just don't want to bother our main road very much. If we had them connecting two highways, it most likely jams. I warned you

There are some examples of service interchanges. You can google some more or even build your own

The first one is a diamond interchange. Pretty cheap, pretty compact (especially the tiny version), handles quite a little traffic, which is enough to connect a couple of farms to an arterial road that connects to highway


The second one is a dumbbell interchange. This is basically an upgraded diamond so the idea is same, but now we have two roundabouts at both ends of bridge so now more trucks can pass


The third one is a partial cloverleaf (parclo). Can be made in very variations (google it, they are mostly the same), takes quite a space and has two lovely loops away from other slip lanes. Pretty useful to connect arterial roads to highways


And, of course, roundabouts

The simplest one looks like a one-way road looped clock- or counterclockwise and its size can be adjusted if needed. But remember one thing – never trust roundabouts. Never. If the traffic is consistent on them, it will cause a gridlock sooner or later. What is the reason? In the case of real-world roundabouts, traffic on the circle has the right-of-way. In the game, there is no such thing. This is what makes roundabouts unreliable. They are worse than loops.They will stab you in the back

But if there is a very little traffic, maybe you can have a small roundabout right here. Just be ready to replace it.

A fun fact: Americans didn't know about that right-of-way rule as well, the holders of this right were incoming cars. This led to collisions and removal of roundabouts all over America. The right-of-way rule in its current form was developed in UK in 20th century, but the Americans have had enough

System interchanges connect a highway to another highway with ramps and connectors. No left-turn conflicts are allowed. They are a bit more complicated and not only I think that – sometimesvery often, especially when there is a loop somewhere PF can't find the best way through an interchange and takes a different route, which is not only longer but conflicts with other routes that have its right to be on that way. When I built my first interchange and started running tests, I saw with my own eyes how the trucks drove correct 75 tiles long way through a loop and then changed their path to the wrong one! And it wasn't even shorter – it was 78 tiles! Mistery...

Before we start talking about real interchanges, let's give the system roundabout a chance. This is a 3-level throughabout with dedicated right and forward lanes
                  This construction makes trucks get on the circle only if they want to turn left

Now we release the trucks...
                                                                     What a surprise

And eventhough all the routes are correct, it has failed

Technically, if we had a roundabout that can let in all the trucks at the same time, it should work, but how big it has to be...
     Look at these “ghost” trucks – they didn't even make it to their warehouses after removal of
                                    previous roundabout, and there is already a gridlock

Nevermind. Just forget about roundabouts.

        I have no idea what I have done, but I called this thing a 2-level spiral roundabout. It barely
              handles all the traffic, takes up just a 11x11 squarethe best result so far and looks
                                                       very similar to star interchange

                              But this dumb PathFintard can't take it. Don't build roundabouts


The most known type of 4-way system interchange since the thirties is a cloverleaf. A little brother can't be build with urban roads, otherwise trucks will never take the loops
                                           A small boi cloverleaf and his bigger brother

Both of them are decent interchanges and do their job, but there is a couple of downsides that make these brothers kinda unreliable

The first problem is the loops, and a cloverleaf has 4 of them. It looks like PF hates loops, so it will even choose a longer way just to avoid taking a loop (yeah, a 78 tiles long way that I mentioned above – it was a cloverleaf). May be it hates loops because a truck will actually go a few tiles back instead of moving forward... Who knows

The second one isn't some wierd in-game bug but a real world cloverleafs problem. It is weaving. I could try to explain this, but look at the picture instead
     Blue and yellow lanes are merging and diverging in the center of direct traffic. In the real world this is dangerous and makes cars to crash, in the game this just makes traffic flow slower

We can try to fix these problems by relocating loops somewhere else...
And we got an another parclo variation. That looks better, but makes it even harder for PF to find a correct path and costs one and a half times more. So just use the cloverleaf. It's not perfect, but simple and does its job

Or build something like this monstrosity
That one is huge and ugly but works like a charm. The name is double-trumpet. It has all its intersections away from each other, so the PF shouldn't mess it up

Or just go for a little swastika if it is not forbidden in your country. This one's called star interchange yes, this is the thing that was similar to 2-level roundabout, pretty stable, but has a lot of intersections, which means slowdowns
                                                     Autobahnkreuz macht Straßen frei

In the previous chapter, the available space for the text has run out

But what if we need to connect 3 roads together?

If we talk about small service interchanges then just use the same ones – diamond, dumbbell, parclo – should be pretty much enough

But if we need to connect 3 highways , we have to think a bit... What if we take a cloverleaf and cut it in half? Let's see...
This is a half-cloverleaf, cute and compact 8x9 size, but there are loops the game hates loops and weaving... What else do we have? A double-trumpet? Huh, what do we get if we cut a double-trumpet in half...

A trumpet interchange! And his bigger highway brother
Actually, this is the only one 3-way interchange you have to remember. Really. It is simple, has no weaving, can handle quite a traffic and PF does not complain

The direct 3-lane merge has a bit more intersections than trumpet interchange, takes a bit more space, but does pretty much the same job and looks a bit less ugly
                                          Just go ahead and merge all the lanes with ramps

Yes, I know, this is the wrong game and LM shouldn't really work there... Or should? The answer is yes, it works, but not really

Let's take a look at the intersections we've build it previous chapter
This is a huge cloverleaf. It is a bit more stable than the smaller version, but look at the direct paths – we have 8 one-way roads and their left lanes are empty!
                                          Also, we have 2 conflict points at each loop

To make trucks use left lanes we have to create an intersection with a left-hand turn somewhere... May be there?


Great! Now all trucks pick their lane at the beginning of their way through the cloverleaf. They take left lane if they want to go forward and the right one if they want to go through a loop. And all trucks that are incoming from a loop will pick the left lane. Eventually, we have one less conflict at each loop – the most tricky part of the intersection

With LM, you can upgrade basically everything that has loops. A half-cloverleaf, a trumpet, a parclo – just think about where to place the left-forward intersections. Some interchanges (star, double-trumpet or 3-lane merge) allow left-lane usage from the box, so no tweaks required. But not by bread alone...

Here is a bit more practical problem. Let's say the cloverleaf is very busy and we want to make a direct route from C to B and also bring something to Z
                                                       Connecting all the routes together

Now we see that all outcoming traffic from C uses right lane and all incoming traffic to B and Z uses its right lane as well. Let's create an artificial left turn

And now who goes forward takes left lane, who goes right takes right lane

The last problem is that C-to-B trucks take a busy left entrance lane while the right one is empty. So we have to remove the left lane on the route after diverge. How?
With a single lane one-way road
                                              Now it flows perfectly. Biffa would be proud

The first thing we must remember is that we always can manually create a direct path from one place to another without going through warehouse. There are some exceptions, of course. For example, if we have a master-warehouse close by to a city with shops within its radius, then these shops will send their own trucks to warehouse so we won't pay for any vehicles to deliver goods. Or if we must send some produced far away goods to the master-warehouse – when we talk about long distances, it is a good idea to use a route between two warehouses because their trucks have capacity of 2 (3 with upgrade) but not 1 like any other, which means less traffic

However, if our production chains are complicated or we just hate math or clicking too much, we can let warehouse automatically send required amount of things to all the places, which means more traffic but less losses of braincells

How many routes lead to a typical warehouse? A gatherers route (water siphons, sand collectors, lumberyards, mines and other things that require some special tiles like coast, forest ora-ora or ore to produce, which means they should be placed in a certain place), farms that require a lot of empty space to function, factories that should be placed in a decent distance from everything else because of pollution, and a trade route – after we created our goods at factories we should deliver them to shops or better to another warehouse (due to higher capacity of warehouse trucks) and then distribute

So we have to deal with 4 routes. A warehouse has one entrance tile and one exit tile, each of them has two lanes. With proper usage of Lane Mathematics™ we can make a single warehouse serve two in- and output routes without making trucks to stop at intersections. Use both entrance and exit lanes of a warehouse if possible. Since we have 4 incoming routes, there still will be at least 2 merges, and the only thing we can do is to not make any other intersections whatsoever. How? With ramps

Now we have only 2 conflict points. But some intersections aren't close to the entrance and exit. We can do better

Let's cook a warehouse spaghetti with my illustrated step-by-step recipe
                                                                            Yammy

UPD. While I was writing the guide, I had no idea I could upload all my creations to workshop. But a good soul has made this complicated warehouse setup and shared it with us. You can go and get it there. Thank you, CharChar. ^^

Pretty much the same, but we merge the lanes later and diverge them earlier, and the design is a bit more compact. You can connect whatever you want in any order. If you have just a few gatherers and farms, you can merge them in a single lane and have two different lanes for factory routes or transportation

                                                                      11x11 and 11x9

Now let's build 4 warehouses around, fill their trucks with water, dispatch them to our test subject and see how it flows through the spaghetti and by its own
                                                                  You see the difference

Actually, this design can be expanded to unlimited number of routes, the problem is that your warehouse still has just two lanes, so... uh... I can not suggest you to build this disgusting abomination. It does not exist. It does not exist. It does not exist. It does not exi

                                                                          God help us

Now let's put this all into practice. Meet my little industrial district. There are 33 buildings in its radius and no manual orders at all, nor irrigation towers. Everything goes to and from the “production” warehouse

I know that I could send flour straight to dough fabric, and send dough and cider to donuts bakery and have less traffic but I don't want to. I don't want manual optimizations, I have automatics. I put down a nice spaghetti nearby the “production” warehouse, a trumpet interchange on the way to the factories to prevent it from jamming and a couple of diamond interchanges and roundabouts where the traffic has begun clogging Yes, I remember what I said about roundabouts, but there is such a little traffic so we can go with it. And that's it, no jams, and I can add some more buildings, it still flows

And if I use all the optimizations, such as irrigation towers and direct production sending, I can place as many buildings as I want until there is no more space around

Now let's remove all the traffic tweaks of mine. No “spaghetti”, roundabouts, interchanges – it's all gone
                                                                 Dead. Not big surprise

In case of long distance transportation, trains can be a wise choice. However, this guide isn't about the trains and I don't think you'll ever need that one. But there is good news – all those intersections we've built can be applied to trains. And we can make them even better using diagonal tracks and do not care about lane mathematics and all that stuff. Magnificent, isn't it? Just remember that the trains run on the left side of the way, it's a bit confusing. And if you want to build a railway network and jam it to hell really hard, go play OpenTTD. You can download it from Steam, it is open-source and free.

Q. My interchange doesn't work. Trucks are going by wrong ways
A. Double-check all directions of the roads, there may be a dead-end somewhere. The game just loves to change the directions when you connect something to current lane or just looking the other way for a moment. If it's all right or all left – depends on lane, check how long the wrong and the correct ways are. If the wrong one is shorter – well, we can't blame PF for picking that one. Try to shorten the correct way, or make the wrong one longer. And if the length is also fine, it might be that PF just haven't found the correct way for this route. Just wait a minute or two, looks like it won't stop searching for a shortcut forever. If it finds, the jam will disappear by itself very soon

Q. My interchange is absolutely correct and at first the trucks were running on the proper way, but now they pick a wrong one which is even longer!
A. Yeah, PathFintard may do that and you can't help it. At first, get rid of that cloverleaf and build something better instead. If it didn't help or if it was not a cloverleaf, try to make short ways shorter and long ways longer. If it didn't work as well – prayeth. If the wrong route passes through a urban&one-way lanes merging, try to replace the urban road with a longer piece of highway. It may help

Q. How do I even know which way my trucks are going? How to display this?
A. If you use manual orders, open a destinations panel and hover you cursor on the corresponding tab - a blue dotted line will appear. If the building works in the auto mode, open its panel and find a “toggle route lines” button on top of it. The button looks like 2 parallel arrows

Q. I'm tired of repeatedly building the same interchange over and over again. How do I save a blueprint or something?
A. There is a “Layout mode” (the button at the bottom and right on the panel) where you can create a new layout by pressing a "create new layout" button and selecting your interchange or whatever you want. Don't forget to rename it (click on the name label after creating)

Q. I've got a bridge bug – whatever bridge I put down, the game replaces it with an urban/one-way bridge instead
A. Try to build the bridge one tile away

Q. How to enable the top-down view?
A. Press F8 That one goes for F8ctorio

Well, this is almost over, you can stop reading now. This is my first guide I've ever created (and the last one I guess) and it took quite a work. Now, even if you can't fix your traffic, you can crush him with your intelligence

By the way, all my playgrounds were stably working all the time I was writing this guide and drawing schemes lol. It definitely works. In total, I had more than 30 warehouses and a few hundreds of trucks deployed at the same time

It wasn't easy to create this guide at all, but I have to thank all that soft I was using for this
                                                                      I hate you guys

Anyway, thank you for reading this pamphlet. Wash your hands, yell at me in comments and never, never trust roundabou-a-argh...