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Parallel Flow Intersection v1

THIS REQUIRES USING TRAFFIC MANAGER. To make this intersection work as in the video, you'll need to set up a timed light system. I'll try my best to explain how that works here. I've also uploaded another version, which has 2 lanes for turning left for even greater capacity.

The Parallel Flow Intersection, or PFI, is a way to considerably increase capacity over a standard intersection without using multiple grades and flyovers. Where a standard intersection has four phases, beacuse of left turns, the PFI has only two phases. It does this by allowing left turns to take place during the other two cycles. While through traffic is stopped at a red, cars can turn left across the other lane of the road, to a side road parallel to their destination. Then, when that road is stopped, cars are free to cross to the proper lane without interference. It requires very little space or cost, and works perfectly for building a realistic looking city, all it requires is properly setting up a system of traffic lights.

First of make sure you've downloaded Traffic Manager and a version of NEP, if you don't have them already. (I used the small version of the four lane road). Here's a guide to using Traffic Manager

Also I'd suggest watching that video by GF Parsons explaing how the PFI works, the graphic for its phases is at about 4:20.

1. Plop the intersection down where you want it.

2. Alright but now to make it work, first we're going to use "Lane Connector" to assign where traffic is turning and which lane it's using. It's a good place to start since it will help you understand how you want traffic to proceed through the intersection before we figure out how it can navigate opposing traffic.

So an introduction for drivers on proceeding through the PFI...

First off, to turn right you'll want to start in the far right lane, then take your first right onto the side street, then right again to your destination.

To head through the intersection in the same direction, start off in the central lane of the 6-lane road, then enter the outside lane of the four lane road after the first light, continue through the intersections in the center, then into the far left lane of the next four lane road (traffic turning right onto the road will be using the lane on your right), then finally into the middle lane of the 6 lane road on the other side of the PFI.

To turn left, take your first left, just before the central intersection onto a side street, then onto the far left lane of a 6 lane road as it leaves.

All of the three lanes of any direction entering the PFI will be going through on their own dedicated lane to their destination (this is the easiest way to set up the PFI, there's a more complicated way to allow traffic to freely switch lanes as it leaves, I'll talk about that at the end)

3. Use "Add Priority Signs" to make sure that traffic proceed directly through the intersection in the center (the orange and white diamond).

4. Use "Juction Restrictions" to allow traffic entering the central 5 intersections to enter a blocked junction. It's the icon of a car rear ending another. We want that to be green :). Before entering a road segment, cims check to see if there's enough room before the next intersection to make sure they won't be stranded in the Keep Clear Zone. We need to turn this off, because the road segments are so short here otherwise they will stop at each one of these intersections, even when their light is green. This took me forever to figure out.

5. Okay, now' the tricky part. We have to set up the traffic lights. A PFI in real life uses 5 lights, however because of the way cities skylines works, we're going to have to set 8 (all four intersections right around the central intersection the game considers seperate even though IRL they would be controlled by a single light). But there are only two phases, alternating which road is allowed to proceed forward. So not so difficult.

First off use "Timed Traffic Lights", and select all the nodes except for the one in the exact center. Eight in total. We're going to click "Add Step", set up how we want the lights in phase 1, then the same for phase two. Where we need a seperate left turn or right turn arrow , click "change mode" next to the light. Several of these lights will be set to always be green.

I posted a picture of traffic lights in their two phases, so you can copy that, although I know it's a little hard to see. Here's a description of what's supposed to be going on as well.

Phase 1- NORTH/SOUTH
Traffic proceeding directly north to south or vice versa, is allowed to proceed forward. While that is happening left-turning traffic is allowed to leave the east/west road, or enter the east/west road, from the side streets.

Pase 2- EAST/WEST
Traffic proceeding directly east to west, etc, is allowed to proceed forward. While that is happening left-turning traffic is allowed to leave the north/south road, or enter the north/south road, from the side streets.

Traffic making a right will always be able to proceed freely.

As you may be able to figure out, the total number of cars that can turn left on any cycle is equal to the size of the 4ln segments (about 14 cars). So I would make the cycles relatively frequent.

6. Okay, lets give it a try. Click "Start", and hopefully it should start working. Functioning properly, it can handle a lot of cars. It's really easy to mess up one of the little details. Make sure two opposing lanes weren't accidentally given a green light, etc.

7. Got it working? Well, take a moment and watch it. Personally I think there's something beautiful about an efficient piece of machinery in motion. Either that, or post a comment here saying what's going wrong, possibly with a picture of the lane connections and traffic phases, and I'll try to answer it as best I can.

You may notice that the final light a car sees as it proceeds straight through the interchange will always be green. We can do this, because we set it up so that traffic from all 3 directions has its own lane. Otherwise we'd have to worry about traffic entering the 6 lane roads from the left merging with through traffic from the tail end of the last cycle. You can allow traffic to ent whichever lane it wants, but to do that, you have to either set some short one or two second transition phases to make sure the road is clear (like I did in the video), or you can catch that tail through traffic with a red, to let left turning traffic merge freely. However, we don't want right turns ever to have to wait at a light. You can also build a seperate lane for right-turning cars, that enters at the same place, but with its own seperate always green light (which is how the PFI is supposed to be built IRL). Also, you can use the NEP roads to double the number of left turn lanes, letting 28 cars proceed through per cycle (if you can get them to use both lanes).

Here's an example of a PFI with those changes
http://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=853222491

8. Now the most important thing. Write a letter to your local representative. Tell them how important better transport infrasture is, and what they are doing to reduce congestion. Ask them if they have considered several new types of intersections and interchanges that are being built by innovate transportation agencies across America and Canada, like the Parallel Flow Intersection, the Continuous Flow Intersection, or the Diverging Diamond Interchange. All of these work not by building our roads wider, or taller, but simply more intelligently.

Remind them how much time is lost by average people , how much economic growth is constrained, how much more pollution is emmitted, and how many are motorists are t-boned every year because of one thing, the left turn. Lets kill it. Lets waste our time playing Cities Skylines, not in traffic.