Have you ever noticed that in heavy rain, the wipers of city buses often stand still, but the glass remains clean? This riddle has been exciting the minds of passengers for many years and has become the subject of debate on driver forums. At first glance, it seems that the driver is simply lazy or forgot to turn on the wipers. But in fact, everything is much more interesting - and is connected with the design features of public transport.
In this article we will not only reveal the secret of “non-working” wipers, but also explain why this technique is used in buses, trolleybuses and some trucks. You will learn how the glass cleaning system in commercial vehicles works, what technologies help drivers maintain visibility in bad weather, and why this method not suitable for passenger cars. We’ll also look at myths and real cases where failure to use windshield wipers led to an accident.
Where did the riddle about the bus in the rain come from?
The first mentions of this riddle appeared in Soviet driver's magazines back in the 1970s. Then it was formulated like this: “Why doesn’t the bus driver turn on the wipers during a rainstorm, but the glass remains clean?”. Over time, the question was transformed, details were added about “foggy windows” or “drops that roll down on their own,” but the essence remained the same.
Interestingly, the riddle became so popular that it was included in tests for candidates for public transport drivers. For example, in Moscow educational plant State Unitary Enterprise "Mosgortrans" This question is still asked in bus design exams. And in 2019 he even got into the program “What? Where? When?" as a “question from a viewer.”
- 📜 1970s: first publication in the magazine "Behind the Wheel" as a “challenge for drivers.”
- 🚍 1990s: the riddle becomes part of the oral folklore of car enthusiasts.
- 💻 2000s: The first analyzes appear on the Internet, but with errors in the explanations.
- 📱 2010s–present: viral discussions on social networks, memes and parodies.
Today the riddle has acquired dozens of “folk” versions of the answer - from the absurd ("the driver hypnotizes the rain") to almost correct (“glass treated with a special compound”). But the real reason lies in design features of buses and physics of movement of large vehicles.
Technical explanation: Why does glass stay clean?
The main secret lies in aerodynamics of the bus and the structure of its windshield. Unlike passenger cars, where wipers are the main cleaning tool, buses use a combined system:
- Glass shape. The bus windshield has large angle of inclination (usually 30–45° versus 15–25° for passenger cars). Thanks to this, raindrops do not linger on the surface, but immediately roll down under the influence of gravity and the oncoming air flow.
- High speed movement. At speeds above 40 km/h, the air flow creates laminar layer, which blows drops off the glass before they even have time to linger. This effect is called
aerodynamic self-cleaning. - Hydrophobic coating.Rain-X or AquaPel), which reduce the adhesion of water to the surface. The water collects in large drops and rolls off without forming a film.
But why then do the drivers the wipers still turn on at low speed or during stops? The fact is that aerodynamic cleaning only works when moving. When the bus is at a traffic light or moving in a traffic jam, the wipers turn on pulse mode (1-2 strokes every 10-15 seconds) to remove accumulated drops.
How to check the hydrophobic coating on your car?
Apply a few drops of water to the glass. If they form balls and roll off, the coating is working. If they spread like a film, it’s time to update it.
| Characteristics | Passenger car | Bus/truck |
|---|---|---|
| Windshield angle | 15–25° | 30–45° |
| Self-cleaning speed (without wipers) | From 60 km/h | From 30–40 km/h |
| Frequency of wiper use | Constantly in the rain | Low speed only |
| Type of hydrophobic coating | Optional (applied by owner) | Standard (applied at the factory) |
Myths and Misconceptions: What's Really False?
There are so many myths around this mystery that even experienced drivers sometimes repeat them. Let's look at the most common ones:
- 🚫 “The wipers only come on at high speed.” Not true! The wipers always work, but in different modes. At speed they can do
1 swing every 20–30 seconds, which is invisible to passengers. - 🚫 “The glass heats up and the droplets evaporate.” There is heated glass, but it is designed to remove condensation, not raindrops. The temperature is too low to evaporate water during a rainstorm.
- 🚫 “Drivers save wiper life.” The service life of brushes on buses is designed for 50–80 thousand km, and replacement is carried out according to regulations. Saving has nothing to do with it.
- 🚫 “This only works on new buses.” The self-cleaning effect depends on aerodynamics and not on the age of the vehicle. Even old ones LiAZ-677 or Ikarus-280 had a steep enough glass slope for this.
One of the most dangerous misconceptions is that this method can be applied to passenger cars. In practice, increasing the angle of the glass reduces visibility, and hydrophobic coatings for buses are not designed for speeds below 40 km/h. As a result, the driver risks losing visibility in a traffic jam or in a parking lot.
If you want to reduce the use of windshield wipers in your car, apply a hydrophobic coating (such as Rain-X) and maintain speed above 60 km/h on the highway. But don't give up on wipers completely!
When does failure to use windshield wipers lead to an accident?
Despite the effectiveness of aerodynamic cleaning, there are situations when bus drivers are required to turn on the wipers manually:
⚠️ Attention! According to Traffic rules of the Russian Federation (clause 19.1), the driver is obliged to ensure that the windows and mirrors are clean enough for visibility. If the wipers do not cope with self-cleaning, they must be turned on forcibly - otherwise it may be regarded as a violation.
- 🌧️ Heavy rain with hail. Large drops or hail can damage the glass if not wiped away with windshield wipers.
- 🚗 Driving in heavy traffic. Splashes from cars in front form a film that aerodynamics does not blow away.
- 🛑 Stops and slow movement. At speeds below 30 km/h, self-cleaning does not work.
- 🧴 Worn hydrophobic coating. Over time, it loses its properties, and the water stops rolling off.
There are known cases when the refusal of wipers led to accidents. For example, in 2017 in St. Petersburg the bus PAZ-3205 lost visibility during a downpour and crashed into a pole. The examination showed that the driver did not turn on the wipers, relying on self-cleaning, although the speed was below 20 km/h. The court found him guilty of violating clause 10.1 of traffic rules (“inconsistency between speed and visibility conditions”).
☑️ When does a bus driver need to turn on the wipers manually?
Can this principle be applied to passenger cars?
Many car owners, having heard about “self-cleaning” bus windows, try to repeat the effect on their cars. But there are several here critical limitations:
- Glass tilt angle. In passenger cars it is smaller, so the drops linger longer.
- Movement speed. Aerodynamic cleaning begins to work only at speeds of 60–70 km/h, which is not always possible in the city.
- Wiper design. Used on buses heated flat brushes, and in passenger cars - ordinary frame ones, which fit worse to the glass.
However, you can partially repeat the effect:
- 🔧Apply hydrophobic coating (for example, Ceramic Pro Rain or Nano-Protect).
- 🚗 Install aerodynamic deflector on the hood (increases air flow over the glass).
- 🔄 Use wipers in pulse mode instead of permanent.
Important! It is impossible to completely abandon windshield wipers in a passenger car - this is a violation clause 4.3 List of faults (“the windshield wipers provided by the design do not work”). If you are stopped by a traffic police inspector, you will be fined 500 rubles (Part 1 of Article 12.5 of the Code of Administrative Offenses of the Russian Federation).
How wipers work on buses: technical details
The glass cleaning system in buses differs from passenger cars not only in operating modes, but also in design:
| Component | Passenger car | Bus/trolleybus |
|---|---|---|
| Wiper type | Frame or frameless | Flat with heating and anti-icing system |
| Drive | Electric motor 12V | Electric motor 24V with gearbox |
| Operating modes | Continuous, Intermittent, High Speed | Adaptive (depends on speed and precipitation) |
| Additional features | Washer, rest zone heating | Heated washer fluid, rain sensor, anti-icing |
Interesting fact: in modern buses (for example, Mercedes-Benz Citaro or Volvo 7900) system is used Rain Sensor Pro, which automatically adjusts the frequency of wiper sweeps depending on:
- 📏 Travel speeds (the higher the speed, the less frequent the swings).
- 🌧️ Precipitation intensity (the sensor analyzes the droplet size).
- 🌡️ Ambient air temperature (at sub-zero values, heating is turned on).
In older models (for example, LAZ-4202 or Ikarus-250) the wipers were controlled mechanically - the driver manually adjusted the frequency of swings with a lever on the dashboard. Today, such systems are considered outdated and do not meet security standards. UNECE No. 43 (about driver visibility).
The wiper system on buses is a complex of solutions: glass aerodynamics, hydrophobic coating, adaptive electronics and heating. In passenger cars, this approach does not work due to other operating conditions.
Legal aspects: what does the law say?
From a legislative point of view, the issue of glass cleanliness is regulated by several regulations:
- Traffic rules of the Russian Federation, clause 19.1: “In the dark and in conditions of insufficient visibility, regardless of the road lighting, as well as in tunnels, headlights must be turned on on a moving vehicle. Rear fog lights can only be used in conditions of poor visibility." Although we are talking about lighting devices here, courts often interpret this rule broadly - as an obligation to ensure visibility by any means availableincluding wipers.
- List of faults (clause 4.3): Operation is prohibited if “The designed windshield wipers do not work”. This means that the wipers must be operational and ready to turn on, even if they are not used constantly.
- GOST R 51709-2001: Regulates the requirements for driver visibility. According to him, The windshield cleaning area must be at least 80% of its total area.
In practice this means that:
- ✅ Bus driver does not violate traffic rules, if the wipers are turned off at high speed while self-cleaning is running.
- ❌ But if visibility deteriorates (for example, due to dirty splashes) and the wipers do not turn on, this may be considered violation of clause 10.1 of traffic rules (“inconsistency between speed and visibility conditions”).
In 2020, the Supreme Court of the Russian Federation considered the case of a bus accident MAZ-103 in the Lipetsk region, where the driver did not turn on the wipers during rain and snow. The court ruled that refusal to use glass cleaners in conditions of poor visibility is a gross violation of the rules for operating a vehicle and may result in criminal liability Art. 264 of the Criminal Code of the Russian Federation (violation of traffic rules resulting in harm to health).
FAQ: answers to frequently asked questions
❓ Why do wipers work on some buses even at high speed?
This depends on the model and condition of the hydrophobic coating. In old buses (for example, PAZ-3205) or when the coating is worn, aerodynamic cleaning works less well and the wipers turn on more often. The driver can also forcefully activate them if he considers visibility insufficient.
❓ Is it possible to apply a hydrophobic coating to the glass of your car?
Yes, but the effect will be less noticeable than on buses. For passenger cars it is better to use specialized compounds (for example, Willson Glass Coat or Soft99 Rain Drop) and combine them with high-quality wipers. It is not possible to completely abandon cleaners.
❓ Why don’t wipers always work on trolleybuses either?
Trolleybuses use the same self-cleaning system as buses, but with one peculiarity: due to the contact network, they often move at reduced speeds (40–50 km/h), so the wipers turn on more often. In addition, trolleybuses stop more often, and at these moments the purifiers operate in pulse mode.
❓ Are there buses where the wipers work constantly?
Yes, in some models (for example, Scania OmniLink or Solaris Urbino) is used combined system: the main wipers rarely work, and small “spoiler” blades along the edges of the glass clean areas where the aerodynamic flow does not reach.
❓ Could the lack of wipers be the reason for the refusal of a technical inspection?
Yes, if the wipers faulty or missing. According to clause 4.3 List of faults, a vehicle will not pass inspection if the windshield wipers do not work. However, if the wipers are working properly, but are turned off while driving (for example, due to self-cleaning), this is not a violation.