Interchanges: the Good, the Bad, and the Ugly

Part 2 of 2: System Interchanges

Construction at the Springfield Interchange (c) Virginia Department of Transportation,
CC BY-NC-ND 2.0

In last week’s edition of Interchanges: the Good, the Bad, and the Ugly; we took a look at the best, the worst, and the meh-st of service interchanges – interchanges connect a highway to smaller or slower roads. System interchanges connect two different highways together. These interchanges are often more complex, traveled at a higher speed and more important. In this second part of this series, we will be exploring the good, the bad, and the ugly of system interchanges.

The Good: Stack Interchanges

Yan’an East Road Interchange, Shanghai (c) Denys Nevozhai, CC0 1.0

The stack interchange, sometimes known as a butterfly interchange, is arguably the most efficient interchange design in the world. Stack interchanges completely eliminate the problem of weaving, where traffic attempting to leave the roadway at the next junction and traffic attempting to enter from the previous junction intersect with each other. Weaving is dangerous and inefficient, and the stack interchange’s ramp design completely eliminates it by having all on-ramps after the off-ramps. As well, due to the relatively gentle curve of the interchanges ramps, it is efficient and most important safe at dealing with large traffic from all directions. While some say that stack interchanges are an eyesore (often being compared to bowls of spaghetti), they actually use significantly less land than our next interchange.

The Bad: Cloverleaf Interchanges

Cloverleaf interchange (c) Anders Sandberg, CC BY-NC 2.0

The cloverleaf interchange is a bad interchange. Full stop. A cloverleaf interchange is an older kind of interchange, built in a minor that resembles a cloverleaf. All left turns are handled by large ramps that make 270-degree turns, while right turns are handled by simple slip lanes. One of the many issues that plague cloverleaf interchanges is that large trucks can tip over on these sharp corners. There are a couple advantages: they are free flowing (meaning they have no traffic lights) and because they only have one bridge, they are cheap to build. However, in my opinion, this does not make up for their many shortfalls. These interchanges suffer from huge problems due to weaving, severely restricting traffic flow. As well, cloverleaf interchanges take up a large amount of land.

The Ugly: Spaghetti Junctions

File:Spaghetti-Junction-Crop.jpg
The Original Spaghetti Junction (c) Highways England, CC BY 2.0

I know what you are thinking. But, you say, we already went over spaghetti interchanges! You said that stack interchanges were like bowls of spaghetti! And you wouldn’t be wrong if you thought this. However, while stack interchanges do come what resemble a bowl of tangled pasta, there are many more worse and less orderly examples of the noodle road menace. A spaghetti junction is a network of complicated, often asymmetric ramps making up an interchange that really does resemble a bowl of spaghetti when seen from above. Since these interchanges vary so wildly in shape it is impossible to say anything about their general effectiveness. It is safe to say, however, they gain points for creativity but lose points for confusion. No matter how well traffic flows through these interchanges, they will still look like a big ugly pile of noodles.

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