I'm the city designer for a new city we're calling Morrowville. Having some of the worlds top minds, flying cars have been invented, but can only fly a few feet (2-4) from the ground and not everyone has made the switch, so roadways are still required. I've proposed a number of traditional roadways to the city and tried to reduce traffic where possible, but was told the designs weren't "innovative enough".

I've been tasked with making all roadways (streets AND highways), with 3 levels, to give the city a futuristic feel, and to provide the city with extra zoning space for businesses and houses. I have had no problems with the base design yet, but I'm having a significant amount of trouble when it comes to intersections and layer traversal.

The levels need to be able to merge vertically and horizontally at designed intersections, similar to freeway heights. For instance, on a normal road, one might need to turn right off the freeway, and would simply get in the correct lane and turn right. On this new design, I could have a possibility of needing to turn right onto the upper road from the middle or bottom road perpendicularly. I also need to be able to get from the bottom road to the top road in the same fashion, and there are only three requirements for the road.

  1. It must be 3 levels, all traversable from any roadway.
  2. It must not slow down traffic unreasonably (No stopping for some high speed elevator).
  3. It must be compact, the normal cloverleaf intersections for 2 directional roads apparently "just doesn't work" for them.
  4. No budget, this city is the future!

Material requirements are met, and businesses/houses need to be able to be placed along this, although for highways and freeways the railings will prevent that except for at designated toll booths. We're just waiting on the design, so please help me keep my job!

How can I make a 3 level roadway that has easily traversable intersections and traffic alleviating properties?


  • Time period is 59 years from now.
  • Technical requirements can be stretched, but I'd like to keep it relatively plausible. No blatant hand waving like portals.
  • There's no magic in this world.
  • The businesses on each level are class based. Middle class in the middle, you get the picture.

Edit: Please excuse my atrocious artistic abilities.

Every single area needs to connect.

I need every single area to connect, and find that the roads will cross no matter what traditional pattern I use.

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    $\begingroup$ This is no different from highways nowadays, and we do have hovercraft that can life more than that from the ground. $\endgroup$ Commented Oct 30, 2018 at 14:47
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    $\begingroup$ Alright y'all, either put those into answers, or please use upvotes on the initial comment talking about "it already exists". It doesn't exist where I live, and "3 level roadways" didn't turn up much useful info. $\endgroup$
    – Anoplexian
    Commented Oct 30, 2018 at 15:17
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    $\begingroup$ en.wikipedia.org/wiki/Multilevel_streets_in_Chicago $\endgroup$
    – Separatrix
    Commented Oct 30, 2018 at 15:29
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    $\begingroup$ "can only fly a few feet (2-4) from the ground" - this makes it pretty much indistinguishable from regular highways, because, without a ramp, a car needs to go 15+ feet in the air to move to the next level. $\endgroup$
    – Alexander
    Commented Oct 30, 2018 at 16:15
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    $\begingroup$ We still need roads and ramps. And if flying and non-flying cars have to share the road, it would be much better to build just one type of roadways that suits both types of vehicles. $\endgroup$
    – Alexander
    Commented Oct 30, 2018 at 16:36

2 Answers 2


I'd propose standard intersections for all horizontal crossings (minimal traffic disruption with efficient AI controlled signalling). All vertical crossings are handled with spiral distributors.

enter image description here

White lines indicate medians.

Horizontal Junctions. Traffic following any of the blue paths (left turns) will be guided by yield / caution signals. Traffic following red paths (right turns) and all through traffic will be guided by stop / caution signals that are integrated with traffic flow monitoring systems.

Vertical Junctions. Traffic flowing from level to level (spiral turns) will be guided by yield / caution signals. While a "level 1 to level 3" spiral could of course be built, its practicality is of dubious nature. Dividing the bi-level spiral into two single-level spirals saves costs and maximises utility.

NB: in the picture, only the left-moving "down-spirals" are shown. I.e., those spirals bringing left-moving traffic from level 3 to level 2 & from level 2 to level 1. The "up-spirals" for left-moving traffic would be off to the right of intersection. Likewise, only the right-moving "up-spirals" are shown. Right-moving "down-spirals" would similarly be off to the right of the intersection. Similar "spiral towers" would also be constructed for the orange / green / yellow roads.

An actual traffic spiral, as used in a car park:

enter image description here

  • $\begingroup$ +1 for the hand drawn lines, but accepted because it's more elegant than what I had so far. $\endgroup$
    – Anoplexian
    Commented Oct 31, 2018 at 14:11

Each stack of roads is one-way. Neighborhoods feed to/from the correct road directions of their block and level via quarter-loop side-streets. Unfortunately, this means that half of the blocks need to be served to/from fast lanes of their adjacent roads.

On some blocks, there are a pair of stacked ramps adjacent to the slow lane. On some blocks, the pair of ramps goes up to the next level; on other blocks, the pair of ramps goes down. On each level, there is a speed-up/slow-down lane that continues from one ramp either to the next ramp, or to the next turn.

Turns occur at the crossings of roads on the same level. Turns connect a speed-up/slow-down lane to another speed-up/slow-down lane. If the fast lane is on the left, all of the turns are right-turns.

There are no clover-leafs. To make a U-turn, you go half-way around a block. To make a left-turn, you go three-quarters of the way around a block.

You can have different speeds on different levels. You might have one level buried, one level at the surface, and one level elevated.


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