[Automotive Tips] Dangers of Slippery Manhole Covers for Motorcycles and Cars
💦 Editor's note: Slippery manhole covers are the most invisible trap for street cars
Hong Kong's roads aren't just made of concrete and asphalt; they're also covered in a variety of metal surfaces—the most common of which are manhole covers (commonly known as "water traps"). These manhole covers are harmless during normal times, but when it rains and gets damp, they become a slab of "street ice" for drivers, especially those on two-wheelers .
1️⃣ Why are wet manhole covers so slippery?
Let me break it down for you:
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Material problem <br>Mill covers are usually made of cast iron or steel, and the metal surface itself is much smoother than asphalt.
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Limited surface texture <br>Some lids have patterns to prevent slipping, but these have been worn out over the years and mixed with dust and mud, making them less effective.
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Lubricating effect after being wetted with water <br>Once water is applied, it is like adding a layer of "oil film" to the metal, and the friction drops sharply.
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Oil accumulation <br>Many manhole covers in Hong Kong are covered with oil stains from vehicles. When it rains, the mixture of oil and water makes the area more slippery.
2️⃣ Motorcycles vs. Manhole Covers: Why Are They More Dangerous?
For motorcycles (motorcycles) , the danger level can be doubled:
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Small contact area <br>The area of contact between the two wheels of a motorcycle and the ground is very small. Once they touch the slippery manhole cover, the friction drops sharply and it is easy to slip.
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Single point reliance <br>If one of the reels hits a manhole cover when turning, it may instantly lose grip, causing a "side slide" or even a "crash".
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Tilt effect <br>When a motorcycle enters a curve, it will tilt. The wet manhole cover is as slippery as ice, and the center of gravity will be immediately out of control.
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No room for error <br>If a four-wheeled vehicle skids, it still has three wheels for support, but if a motorcycle skids, both the driver and the vehicle usually fall.
3️⃣ Car vs. Manhole Cover: Stable, but Not Innocent
Although cars have four wheels and are much more stable than motorcycles, they still have risks:
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High-speed cornering <br>If both wheels on one side hit the slippery pothole cover at the same time, one of the tires may lose grip instantly, causing oversteer or understeer.
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Increased braking distance for heavy vehicles <br>When a bus or truck brakes over a wet manhole cover, the braking distance is longer than on asphalt pavement, increasing the risk of collision.
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High ABS intervention frequency <br>When braking over wet metal surfaces, ABS will intervene frequently, making the brakes feel "loose" and the driver may not be able to react quickly enough.
4️⃣ Special circumstances in Hong Kong
There are many manhole covers on Hong Kong roads, and their distribution characteristics are:
- Curves (sloping residential roads, village entrances, narrow streets in old districts)
- Bus station entrance/exit (the weight of the bus damaged the asphalt, and the Hong Kong government covered the manhole cover with metal)
- Before the traffic light (for underground drainage)
- Tunnel entrance drainage level (more slippery when it rains)
In addition, Hong Kong has frequent rains, and the roads are sometimes not dry after the rain, so manhole covers become "hidden traps".
5️⃣ Real Risk Case (Hong Kong)
The editor checked the traffic accident news:
- A motorcyclist skidded near Tsuen Wan West MTR Station due to a slippery large manhole cover on the inside of a bend. He was sent to the hospital with minor injuries.
- A taxi on Canton Road in Yau Ma Tei was turning right in the rain when its front wheel hit a manhole cover, causing it to slip and crash into a lamppost. Fortunately, the driver was not seriously injured.
6️⃣ Editor's anti-slip advice💡
Motorcycle driver:
- Find the line before turning and avoid manhole covers : Observe the road surface before entering a turn and try not to lean on the manhole cover.
- Going through the cover in a straight line : If you can’t avoid it, remember to go through it in a straight line to reduce the risk of slipping.
- Keep the throttle smooth : avoid sudden acceleration or reduction of the throttle.
- Be extra careful when it rains : especially during the first 15 minutes of rain, when oil pollution is heaviest.
Car Driver:
- Slow down when going over the cover : especially when going downhill or entering a curve.
- Avoid sudden braking : Metal surfaces have poor braking effect, so it is safer to slow down in advance.
- Keep the steering wheel steady : Do not steer suddenly in slippery conditions.
Other driving tips:
- Be familiar with the distribution of manhole covers along common routes
- Using car headlight reflections to identify manhole covers at night
- Be gentle when turning the line over the cover
7️⃣ Editor’s Summary
Whether it's a motorcycle or a car, a wet manhole cover = a potential loss of control .
While slippery roads in Hong Kong are commonplace, many drivers may not fully appreciate the dangers of slippery manhole covers. Motorcyclists, in particular, should make avoiding manhole covers a reflexive driving habit, like stopping at a red light.
Metal surfaces + water + oil stains = Hong Kong's "invisible killer"
There is no life at stake. It is better to be a second slower and safer than a second faster and risky.
