Poly Bridge 2: Bridging the Gap Between Engineering and Gaming

Kathryn Minor
12 min readMar 24, 2023

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Poly Bridge 2 presents players with a seemingly straightforward task: construct a functional bridge. Created by Dry Cactus, Poly Bridge 2 is available on Windows, Linux, Mac, Android phones, and even iOS (Where I played it!). Although the game is not intended to teach players how to build a fully-functional bridge in real life, it does offer a solid introduction to the fundamental principles of bridge construction. As players work to construct their bridges, they are able to learn key construction strategies such as creating triangles, diamonds, and trusses. If you’ve ever looked at a bridge and wondered “Why does it look like that?” this game has answers for you!

The bridge I drove past every day in my home town , the Big Four Bridge in Louisville, Kentucky. It spans across Ohio River and connects Louisville to Indiana.

Like most games, though, this core task of constructing a functional bridge becomes increasingly intricate as the game progresses. In the initial level, all a player is required to do is assist a single car in crossing a gap. However, just a few levels later, players must build a drawbridge utilizing hydraulics which permits a boat to pass underneath.

One of the bridges I built using hydraulics to allow for a boat to pass underneath.

Despite the fact that levels become increasingly complex, Poly Bridge 2 levels follow a consistent structure. This familiarity instills a sense of confidence; They can approach the stage without the fear of the unexpected. A random boat won’t appear during a stage where it wasn’t previously mentioned. Whether players are challenged with transporting a single car or multiple trucks to various destinations, the game clearly establishes expectations. Each level follows this structure, or gameplay loop:

  1. First, players survey the level and assess the size of the gap they need to bridge alongside the obstacles they need to overcome (such as boats, multiple checkpoints, and even heavy vehicles).
  2. Next, players review the budget and the materials available to them (Players can have access to roads, reinforced roads, wood, steel, hydraulics, rope, cables, springs, and bungee ropes).
  3. Using their previously acquired bridge-building knowledge, players begin constructing their bridge.
  4. Once complete, players test their bridge in Poly Bridge 2’s bridge simulator.
  5. If they fail the level, players can refine their bridge until they succeed or until they are happy with it.
An example of a level start screen.

This last point about player happiness is quite significant as, during my time playing Poly Bridge, a successful bridge didn’t necessarily mean I hurried myself onto the next. Despite the vehicle’s successful journey, I wanted it to be the best I could do. I felt compelled to continue my bridge as I knew it could be enhanced further.

My first attempt at building a bridge in level 1–03 which is barely under budget and ugly (plus the triangles go higher than needed, making it more expensive)
My final iteration of level 1–03 which is cheaper and looks much better.

Typically, my goal in improving my bridge was to increase the cost efficiency or the aesthetic appeal. Particularly in earlier levels, my refinements were motivated by my goal to achieve symmetry or decrease the amount of used material. As I progressed, I learned to streamline my bridge-building approach to reduce the amount of iterations.

A symmetrical and beautiful bridge, my magnum opus.

The strategies I learned to reduce bulk, achieve greater symmetry, and better accommodate for differing weight requirements were applicable throughout all levels. The fact that I was able to learn these skills in just six levels is a testament to Poly Bridge 2’s educational value. My approach in the later levels was much more sophisticated than in the initial ones. In these later levels, the game had explained to me and, through trial and error, helped me to understand strategies like triangles, trusses, and diamonds. These add structural integrity to a bridge and have a much better success rate than a road with no support.

A wonderful bridge that just needs a little bit of work. Maybe a little bit more than a little bit of work.

The skills and principles learned in the game actually do transfer to real life applications; The game is even used in educational settings. Check out the education version here. Poly Bridge 2 offers a safe platform for beginner bridge architects to gain a foundational knowledge about constructing successful bridges without the risk of catastrophic failure. As the construction strategies in Poly Bridge 2 are used in actual bridge construction, the transfer is clear, this game is a valuable educational tool for this obvious use case.

This is not where firetrucks belong.

Moreover, the game’s educational properties extend beyond bridge building, as the principles of stabilization taught in the game are applicable in a variety of contexts. From building a card house, to carrying a load of dishes from the oven to the sink, and even playing Jenga, understanding the stabilization principles taught in Poly Bridge 2 can be applicable in even the most unexpected situations.

A house of cards using the same triangulation technique as Poly Bridge 2.

But how is Poly Bridge 2 able to successfully teach bridge-building skills? Especially for people like me, someone who has only ever looked at a bridge and asked “Why does it look like that?”

Poly Bridge 2 builds upon 3 key assumptions about its players:

  1. Players understand what a bridge is.
  2. Players understand bridges are made of materials like steel and wood.
  3. Players understand that a bridge’s goal is to make it possible to cross untraversable terrain.
Kinds of bridges and their strategies to beat physics.

These assumptions serve as the bedrock for the game’s educational objectives, emphasizing the idea that anyone can construct a functional bridge. Beyond the primary goal, the game also has three additional educational goals.

  1. Teaching players how to build a bridge within a budget
  2. Familiarizing players with the impact of different provided materials on a bridge’s effectiveness
  3. Helping players account for obstacles (planes, boats, multiple checkpoints) in the building process.
What players are up to after they finish every level in Poly Bridge 2.

With these goals in mind, Poly Bridge 2 relies on its core gameplay loop, mentioned above, to reinforce these learnings. There are, of course, smaller loops, such as build bridge, test bridge, fix bridge, repeat, that support this larger loop and player learning. In effect, though, Poly Bridge 2 relies on trial by error. Players often fail their first attempt at making a bridge. In fact, players are not expecting to succeed on their first attempt. This teaching method is effective for several reasons, including the following:

1.) Feedback

Players in Poly Bridge 2 receive constant feedback about their work by continuously testing their bridge against the conditions. Even if they are aware their bridge is going to fail, players will often run the simulation just to see how it will perform. During my playtest, I found myself running simulations just to test the limits of the materials and decrease the cost of my bridge. The ability to frequently test the bridge was a key factor in determining what worked and what did not in bridge construction, and it was this aspect of the game that reinforced my learning the most. It helped me to understand where triangles can be effective and where they can be removed.

One of my first bridges with just a ridiculous amount of triangles for one little taxi.

This simulation-initiated feedback is a crucial aspect of the game’s effectiveness in teaching bridge construction. This feedback-centric approach aligns with the Instructional Complexity Principles put forth by Koedinger, Booth, and Klahr, which suggest that feedback during learning is superior to no feedback at all. In fact, the game’s ability to provide feedback when explicitly requested, aka when running the bridge simulation, is even more effective than constant feedback.

Iteration 1 of the first hydraulics level
Iteration 20 of the first hydraulics level

If the game were to provide feedback before the player had a chance to test their bridge, it would feel like the game is leading them to the answer, potentially leading to boredom or frustration. No one likes to be told how to improve their work when it is not yet done. Therefore, the ability to test and receive feedback through the simulation is a powerful tool for reinforcing learning in Poly Bridge 2.

2.) Generation Effect

What I love about Poly Bridge 2 is that there is not just one solution to a problem. Players have the freedom to construct their bridge in any way they would like, no matter how unconventional or nonsensical the solution may seem. Even if it is not an actual bridge, such as a ramp, or even if it is a complex system of hydraulics, players are still able to create a structure which is uniquely theirs.

Poly Bridge 2 self-destroying one-time loop-de-loop

It is important to note that in the process of building my own bridge solutions, I was mindful that there may be someone else who constructed a better, more efficient and structurally sound bridge using fewer materials and with faster vehicle crossings. This flexibility also reminded me that there are likely better solutions out there, and encouraged me to continuously iterate and improve my designs.

Work of a player who understands bridge-building much more than me (but I will get there)

Through constructing my bridges without consulting other player’s solutions, I gained a deeper understanding of why my designs were successful. If I had simply looked at someone else’s bridge, especially with my current level of understanding, I doubt I would comprehend the reasons behind its effectiveness. Observing my bridge throughout each stage of iteration, improving upon it, and increasing its efficiency helped me develop greater familiarity with the construction strategies taught by the game.

A bridge without rope
A bridge with rope (better)

By generating their own answers, learners are able to better connect with the material and gain a more nuanced understanding of the concepts presented. The principle known as the Generation Effect, proposed by Arthur C. Graesse in the Inaugural Editorial for Journal of Educational Psychology asserts this same concept; Learners benefit from being able to generate their own solutions instead of merely selecting from preexisting models. This idea highlights the importance of having a learner create their own artifact, as it promotes deeper understanding and retention.

A bridge that is incredibly over budget vs a bridge without all the bells and whistles that still gets the job done.

This idea resonates with me personally because if Poly Bridge 2 had been designed as a multiple-choice test, I might be able to guess which bridges would work just by looking at it, but I would not learn how to actually build a bridge. Even if I were shown the same bridges and asked whether they would work, I could probably guess the answer, but I still wouldn’t have learned how to construct a bridge myself. By allowing learners to construct their own bridges, Poly Bridge 2 reinforces their learning and helps to deepen their understanding of structural principles.

3.) Weeding

While Poly Bridge 2 is an excellent tool for learning about bridge construction, it’s important to note that the bridges you create in the game may not translate perfectly to real-world situations. Even if your virtual bridge looks the same as a real-world bridge, it might not be structurally sound in reality. This is because the game doesn’t take into account all of the complex physical forces that real-world bridge engineers have to consider. So, while Poly Bridge 2 is a valuable tool for learning about bridge construction, it’s important to keep in mind that it’s not a substitute for a real-world engineering degree.

All available materials in Poly Bridge 2. From left to right: Road, Reinforced Road, Wood, Steel, Hydraulics (evil), rope, cable, coil, and bungee cable.

In a video by Real Civil Engineer entitled “How REALISTIC is Poly Bridge 2? Explained by a REAL CIVIL ENGINEER” he exposes the game’s physics engine does not take into account the weight of materials. Despite the game explicitly stating that steel is heavier than wood, this video shows that in the game, steel and wood are considered equivalent in weight. In fact, all materials have equivalent weight. This contradicts real-life physics. Therefore, while Poly Bridge 2 provides a fun and engaging way to learn about bridge construction, it should not be relied upon for accurate real-world engineering.

Despite this lack of consideration for reality when it comes to weight of materials, it’s possible that the creators of Poly Bridge 2 intentionally overlooked this aspect to simplify the learning experience. In fact, it wouldn’t surprise me if the developers of Poly Bridge 2 KNOW that wood is lighter than steel. For novice bridge builders, mastering new construction techniques, understanding materials, and the intricacies of hydraulics (which are still very mysterious to me) can already be challenging enough without adding the complexity of different material weights.

How the game teaches you about hydraulics.
What the first time doing hydraulics is actually like

Removing the weight aspect from the game can be viewed as an example of “weeding”. This term was proposed by Richard E. Mayer and Roxana Moreno in their paper “Nine Ways to Reduce Cognitive Load in Multimedia Learning”. By excluding this aspect, the game developers have effectively reduced the cognitive load of the players. In reality, it can be difficult to understand how the weight of one material affects another material and so on. However, by ensuring that all materials weigh the same in the game, the learning process is simplified, allowing players to better understand the materials and build more bridges than they wouldn’t have been able to if the game were needlessly complicated by weights.

Player-made weighing system in Poly Bridge 2.

Overall, these three learning principles support the game’s educational goals. To me, the core mechanism that allows for players to learn is the fact that they can continually iterate on a bridge of their own making, receiving feedback in a psychologically safe environment that is free from any over-complications. At its core, this is what allows players to learn all about the basics of bridge construction, even hydraulics, which are weird.

I’m scared

Not only did these principles help me to understand the game’s learning goals, they also allowed me to learn about the key nouns and verbs of the game. To me, the key nouns of the game are bridge, the materials (wood, steel, hydraulics, roads, etc), budget, and vehicles. These are all the components that players must consider while building a bridge. Similarly, these nouns are acted upon by the game’s main verbs, building, testing, and iterating. I would actually say that these verbs actually function in a loop.

Home Page Art for Poly Bridge 2

All of these nouns, verbs, and learning principles work together to ultimately create the game that is Poly Bridge 2. In my opinion, Poly Bridge 2 is highly effective in teaching the strategies for balancing that are not only applicable to bridge construction but also in other areas of life where strategic balancing is crucial. Although the game simplifies certain complicated aspects of physics, it actually does more good than harm in terms of teaching and learning. Removing unnecessary cognitive load helps learners focus on the essential principles of construction, leading to a more efficient and enjoyable learning experience. Ultimately, Poly Bridge 2 taught me more about construction than building a house when I was a Girl Scout. AND I enjoyed it (unlike Girl Scouts).

Introduction to “Wacky Physics” Art

Through its innovative approach to teaching bridge construction and design, the game instills a basic understanding of the principles of structural engineering. After playing the game, I gained the ability to identify the essential components of a bridge, such as trusses, triangles, and diamonds, which are crucial to stability. While I may not be able to improve an actual bridge, I believe this knowledge will prove invaluable as I navigate the challenges of a future job, particularly when I need to create real-life prototypes that require balancing and stability. All in all, I am thrilled to have experienced Poly Bridge 2. I highly recommend it to anyone interested in learning more about the art of bridge construction.

Thank you for reading!

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