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A Rational Approach To Racing Game Track Design

September 6, 2011 Article Start Page 1 of 5 Next
 

[In this extensive article, Gamasutra takes an in-depth look at racing game track design, comparing two arcade titles -- Initial D and Maximum Tune -- and contrasting them, at important points, against the approach used in the Gran Turismo series.]

Games are about empowerment -- being able to achieve and do things that you can't ordinarily (or legally) achieve in real life. Car racing games, especially arcade racing games, are the perfect example of this. Reaching the level of skill required to drive in F1 will be out of reach of 99.9999 percent of the population.

Financial overhead also plays a significant role in being able to drive your car on a race track in real life -- not only do you need a competent car, but you also need to pay all of the fees associated with "legal" racing. The most prohibitive factor though is age and licensing laws -- every teenage boy wants to drive a high-powered car, but that just isn't going to happen in reality.

This is where the humble arcade racer comes in. A well-designed arcade racer gives non-drivers an empowering, and most importantly, accessible experience.

But how do game designers make driving "on the limit" accessible, fun, and most importantly, empowering for non-drivers? The answer to this lies in analyzing the track design of two contemporary arcade hits: Initial D: Arcade Stage and Maximum Tune.

Anyone who has visited an arcade recently would have noticed that these two games dominate the arcade market, and are nearly always played by non-drivers piloting 820-plus horsepower monsters like pros.

There are two sides to this sudden and god-like ability for non-drivers to handle these uber-cars: vehicle dynamics and track design. This article focuses on establishing a set of rational metrics for track design and then applying these metrics to the analysis of the Mt. Akina track from Initial D: Arcade Stage 4 and the Hanshin Express Line from Maximum Tune 3.

Five Essential Metrics

In order to take a rational approach to track design, it is essential that we have a set of metrics. These metrics underpin all elements of track design and can be employed in a number of different scenarios. The five metrics of rational track design are;

  • Metric 1: Race Line
  • Metric 2: Clipping points (and related metrics)
  • Metric 3: Track Width
  • Metric 4: Camber
  • Metric 5: Height Variation

Before analyzing how the case studies provide an empowering experience for non-drivers, it is essential that that these metrics are explained both individually and in relation to each other.

Clipping Points & The Race Line

The most essential metrics for rational track design are clipping point and the race line. However, to understand how these two metrics work, it is important to talk about the vehicle and its system of dynamics. Using the existing Society of Automotive Engineers' standard model, a vehicle has a pre-defined set of axes which are used in all racing games. Figure 1 is an example of the standardized SAE coordinate system.


Figure 1

The longitudinal axis is most directly affected by acceleration and braking. The yaw and lateral axis is most directly impacted by steering and subsequent weight transition. In a racing game, we want the player to apply as much longitudinal force as possible, as this will always result in a high speed. Application of brakes and lateral force will not only slow the vehicle down but also make it less predictable. With this in mind, we can now move onto the concept of clipping points and race line.

The metrics presented in this article are all based on the effect on the vehicle, not the end user. The track will always directly impact the vehicle, but only indirectly impact the driver. The reason for this is due to the fact that driving different vehicles on the exact same road will yield different experiences for the end user.

The vehicle is a translator of sorts, and is the essential middle man between the player and the track design. As vehicle dynamics is such a broad topic in itself, it will be discussed a future article, however the SAE standard axis system is comprehensive enough to be able to understand and apply the five metrics of rational track design.

Metric 1 and 2: Clipping Points & The Race Line


Figure 2

Every corner in a race track will have an ideal entry point, an ideal clipping point, and then an ideal exit point. The clipping point is a target on the roads edge that the player must aim for in order to maximize the chances of taking the shortest possible route through a corner, whilst at the same time placing the least amount of lateral force onto the vehicle (Figure 1).

In some cases, a clipping point might represent the shortest possible route through a corner; however, it may require the use of too much lateral force on the vehicle. These ideal points enable the player to apply as much longitudinal force onto the vehicle as possible (acceleration) without compromising this force with the addition of any unnecessary lateral movement.


Figure 3

Entry, exit, and clipping points are derived partly from creating the shortest possible route through a corner and also from using the most surface area of the road. The reason surface area is important is, if a road is wider, it means that less lateral force needs to be applied to the vehicle (remembering that lateral forces compromise acceleration and also make the car less predictable).

Jumping ahead slightly, Figure 3 has a dotted green line used to denote the race line -- or most optimal route through the corner. The wider the road is, the straighter the race line becomes and less speed-compromising lateral force needs to be applied. In all cases, opportunities to increase longitudinal force are most sought after by players in any arcade racer.

It is difficult to talk about these two metrics in isolation, as they are a product of each other. For a driver, they will create a race line in their mind based on an understanding of their vehicle and the clipping points. From a designer's perspective, the race line may supersede the track layout depending on the approach taken.

No matter what approach of these approaches is used in the design of tracks, the ideal race line should result in the least amount of lateral force being applied on the vehicle. To demonstrate these two approaches, we can refer to figures Figure 4 and Figure 5 respectively.


Figure 4


Figure 5

Figure 4 is the end result of drawing a simple spline to represent your track. Based on this approach, the designer would need to plan their clipping points then create the track around this. Figure 5, on the other hand, is just as valid, and uses the opposite approach. The designer would need to draw on the clipping points, then create the ideal race line. No matter what approach is used, the end result is represented in Figure 6 as a very basic, kart-style layout.


Figure 6

Although this is indicative of an end result, by no means does it represent the body of knowledge that is required to make an empowering track. The next issue that needs to be addressed is corner difficulty, which is a combination of race line and clipping points.


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Comments


Soeren Lund
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Excellent article Luke. Thanks for sharing.

Richard Terrell
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I'm enjoying the clear and thorough approach so far. My main experience with racing games comes from Mario Kart, crazy Taxi., and Excite Truck. The article should help me understand the track design of these games.

David Finlay
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Maximum Tune 3 and 4 are DIRECT rips of the Midnight Club Racing Series created by Rockstar Games. lol, how blatant can it be?! Even the font used in the logo of "Maximum Tune 4: MIDNIGHT". Wow....

Malcolm Tredinnick
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You pitch the clipping point as being the shortest distance + least lateral force through a corner, but that seems to be slightly obfuscating what is really wanted: from a racing perspective, the goal is to get through each corner in the fastest possible time, not to take the shortest route. Least lateral force drives towards that goal, shortest distance is probably less of a controlling factor (a consequence, not a cause). The rest of the analysis still holds up and I do like your presentation, but it seems physically counter-intuitive to talk about shortest distance, rather than least time.

Alison Fernandes
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Malcolm got a point.



There are also 2 other things i found not to be right, what you refered as a Scandinavian Flick is in fact a simple slide/drift which can be easily achieved through some well known drift techniques, this is a Scandinavian Flick: http://www.youtube.com/watch?v=Sbr1K3uuOPk



2nd, "A smaller car like the Toyota AE86 will have more of an advantage in down-hill circuits due to its lower mass and ability to over-steer on corner exits." Shouldn't it be "ability to over-steer on corner entry? When you exit a corner you want to go pedal to the metal, if the car is prone to over-steer on corner exit you will lose grip therefore lose exit speed.



Other than that i liked to read your article, as a regular player of racing simulators ( Live for Speed btw) this lighten me up on what i would have to focus if i am to develop an arcade racing game, abstracting from the realism i'm used to (and like) in offspring of a more forgiving gameplay is harder than i thought lol

Ian Millington
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This is a game effort, Luke, and its nice to see the variables laid out. I loved the concrete examples in pages 4 and 5.



Unfortunately your theory is a wee bit off. The fastest line will almost never be the shortest. For the ideal corners in your initial example you will be clipping at *maximum* lateral force. Corner complexes rarely have a definite entry and exit point. Height variation is used in real tracks to change vertical acceleration. Camber isn't directly related to under or oversteer but to geometric downforce. Understeer and oversteer are caused by differential load front and back. Taruffi's classic "The Technique of Motor Racing" is a good place to start.



But again, the conclusions you come to for game design seem cool.

Soeren Lund
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Also worth noting is that the article only outlines the geometric racing line which is not necessarily the optimal racing line (see for instance: http://www.drivingfast.net/techniques/racing-line.htm).

Luke McMillan
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Thanks everyone for taking a look at my article - I really appreciate the feedback. The race line is rather contentious and I found that it depends on the type of vehicle dynamics system being used as well as the target demographic. For instance, when you are trained to drive a car around a circuit, you are taught to shed speed prior to the corner entry and focus on a higher exit speed. When you don't do this, the combination of weight transfer and frontal grip can often lead to extreme under steer or over steer depending on the characteristics of your vehicle.



I have driven my car on a circuit a few times, and I took this mantra into experiments with Maximum Tune - only to find out that their system of vehicle dynamics actually punishes the player for taking this approach. Through observation, I found that most of the better players did what your not meant to do - shed significant speed AFTER corner entry. What I found was that the designers of Maximum Tune had done was use a clever system which alternates between over-steer on corner entry and under steer on corner exit. Keep in mind though that this was through observation, rather than having an inside knowledge of how they had approached the problem of empowerment.



I have also been doing some experiments using Racer's Pacejka formula to see if it is actually possible to get these simulation focused engines to do something with a distinctive arcade feel. One thing is for certain, there is definitely a significant divide between arcade and simulation titles (and rightly so).



@Ian - Thanks heaps for the info, I will definitely be grabbing a copy of that.



@Alison - Thanks for the comments - that is a mistake in relation to the AE86 example I will make sure that I fix that up in a v2.0 :)



@Soren - I will definitely take that link into account when writing the follow up about vehicle dynamics for arcade titles.

jin choung
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wooooooooow. nice. thanks!

Harry Fields
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Good read, Luke. The force is strong with you.

nicholas ralabate
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Just stumbled across this working on an arcade chase-em-up... so helpful, I wish you would write more articles on gamasutra.


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