Why do painted roads and flyovers become dangerously slick?
Decorative paint smooths out road tarmac and traps a film of water beneath tyres, causing sudden aquaplaning on wet surfaces.
Asphalt relies on micro-texture and open pores to drain water and create mechanical grip between tyres and the road surface. Standard decorative paints fill these porous gaps with a smooth film of resin and pigment, preventing rubber from locking into aggregate peaks. When rain hits this sealed surface, water cannot escape into the pavement texture and instead forms a microscopic boundary layer that causes tyres to aquaplane at normal driving speeds. Safe coloured road treatments require specialised thermosetting resins blended with hard calcined bauxite aggregate rather than ordinary exterior paints.
- Overnight removal
- Kolkata Metropolitan Development Authority engineers, October 2024
- Shaheed Bhagat Singh More
- Paschim Bardhaman district administration, October 2024
- Speed-calming studs and reflectors
- Kolkata Traffic Police, October 2024
- High-level technical inquiry
- West Bengal urban development authorities, October 2024
- Motorcycles and scooters
- Kolkata municipal incident reports, October 2024
What's happening now
Municipal authorities in Kolkata ordered the immediate mechanical scrubbing and roughening of the Chingrighata flyover after rain transformed freshly applied colourful surface coatings into an ice-like hazard for two-wheeler riders. Video recordings circulating across social media showed successive motorcyclists losing traction and sliding across the wet road deck, even while travelling at modest commuter speeds. The carriageway had received vivid decorative coats as part of a pre-festival civic beautification drive ahead of Durga Puja.
Within hours of the recorded falls, municipal and development authority teams mobilised heavy machinery overnight to abrade the painted surface and restore tyre grip. Alongside the physical removal of the coating, traffic police crews installed raised road studs and reflective markers to force vehicles into lower speeds across the elevated corridor. A parallel intervention took place in Asansol, where the local administration scraped away freshly painted road patterns at Shaheed Bhagat Singh More before rain could trigger identical accidents.
Urban development engineers from the Kolkata Metropolitan Development Authority and the municipal corporation were directed to run technical inquiries into the formulation applied to the tarmac. While civic agencies initially claimed anti-skid additives had been specified, engineering inspections focused on why the final film blocked surface drainage and produced severe glare under sunlight. Officials announced that decorative street enhancements would be halted until certified friction-tested surfacing materials could be procured.
How road paint destroys tyre traction in the rain
Sealing surface macrotexture
Asphalt concrete provides mechanical friction through macrotexture, the visible voids between crushed stone aggregates that let water drain away under tyre pressure. Standard liquid paint pools directly into these voids, curing into a continuous, level membrane that eliminates the drainage pathways required for wet-weather grip.
Masking aggregate microtexture
Tyre rubber achieves frictional adhesion by interlocking with microscopic angularities on stone surfaces. Paint resins form a smooth polymeric crust over individual aggregate chips, replacing rough mineral edges with a low-friction polymer surface that offers negligible mechanical grip.
Hydrodynamic water trapping
When water falls on untreated asphalt, hydrodynamic pressure forces the liquid into downward pores as a vehicle tyre rolls over it. Over a painted non-porous plane, the water cannot escape downwards or laterally, forming a thin, continuous fluid film trapped directly between the tyre tread and the roadway.
Loss of contact and dynamic hydroplaning
Because rubber cannot penetrate this trapped liquid film without aggregate peaks to pierce it, the contact patch lifts off the solid deck. Friction drops near zero, causing two-wheelers to slip sideways under modest braking, leaning, or throttle inputs.
Who it affects
Two-wheeler riders bear almost all the immediate physical risk when road friction collapses. Motorcyclists and scooter riders depend entirely on the delicate balance of traction across two small tyre contact patches, each roughly the surface area of a palm. In India, where two-wheelers constitute over 70 percent of registered motor vehicles according to Ministry of Road Transport and Highways data, any sudden loss of pavement friction causes immediate vehicle destabilisation and violent low-side falls.
Flyover ramps and elevated structures heighten the severity of skidding incidents. Elevated bridges feature cross-slopes, bridge expansion joints, and high wind exposures where riders frequently lean into turns or decelerate rapidly on downhill approaches. When sudden friction loss occurs on an elevated bridge, fallen riders face severe secondary impact risks from trailing motor vehicles, buses, and roadside crash barriers.
What's being done, and is it working
Institution
Kolkata Metropolitan Development Authority
Engineers dispatched road-scraping crews to mechanically abrade the painted carriageway surface and installed road studs to curb speed.
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Paschim Bardhaman District Administration
Officials removed newly applied decorative intersection coatings overnight at Shaheed Bhagat Singh More in Asansol.
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West Bengal Urban Development Department
Ordered an engineering probe to test whether road contractors complied with anti-skid specifications or used unapproved exterior paints.
What you can do
Treat painted, bright, or non-standard road surfaces as wet metal or ice when riding in rainy conditions.
Avoid aggressive front braking or sudden lean angles whenever passing over painted lanes, zebra stripes, or decorative art.
Ensure two-wheeler tyres maintain legal tread depths above two millimetres to maximise water evacuation over slick surfaces.
Report untextured painted carriageway sections on elevated roads to local traffic control rooms before monsoon rains.
What we still don't know
- Whether the contractor used ordinary exterior acrylic paint rather than certified high-friction surfacing resins.
- Whether civic procurement standards mandate British Pendulum Skid Resistance testing before coloured surfacing can be cleared on arterial routes.
Questions readers ask
Why does rain make painted road markings much slipperier than bare asphalt?
Bare asphalt contains sharp mineral grains and small drainage channels that allow water to escape under a tyre. Standard paint creates a non-porous flat film, preventing drainage and forcing tyres to glide on top of water.
How do highway engineers safely colour road surfaces?
Engineers apply high-friction surfacing systems, which bind calcined bauxite or hard quartz aggregates into polyurethane or epoxy resins. The hard aggregate chips stick up above the resin binder, maintaining rough texture and tyre grip.
Why are two-wheeler riders most vulnerable to road paint hazards?
Two-wheelers rely on two small contact patches to stay upright. Any sudden lateral loss of grip caused by a slick surface immediately causes the vehicle to tip over, whereas four-wheel vehicles retain mechanical stability.
