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askST: Why do vertical streaks appear on car windscreens?

Reader Danny Yeo wrote in to ask why vertical streaks appear on the windscreens of newer car models. The phenomenon, which hampers visibility during rainy nights, was not an issue with older cars, Mr Yeo said.

Transport correspondent Adrian Lim found the answer.

Streaks can be caused by dirty or worn out windscreen wipers, as well as contaminants on the windscreen surface, said the Automobile Association (AA).

The association said it was not aware if streaks could be caused by the type of glass used in the manufacture of newer cars, and advised car owners to check with their auto dealers on this.

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In general, however, the AA said that rubber wiper blades which are warped - due to exposure to the sun or the environment - could leave streaks on a car windscreen.

Dirt on the blades and the windscreen surface could also be spread across the windscreen when the wipers are used during rainy weather.

Additionally, a lack of maintenance could result in contaminants - such as dust and dirt, road soil, tree sap, and plant litter - accumulating on the windscreen surface.

To remove the streaks, the AA recommends using an appropriate glass cleaner, and a soft microfiber cloth. Apply firm, up-and-down motions along the entire length of the windshield during the cleaning.

To prevent streaks from occurring, motorists are advised to clean their windscreens every one to two weeks, and to keep the wiper blades clean. Wiper blades should be changed at least once a year.

Finally, the AA also suggests using a rain repellent on the windscreen to help water run off without leaving streaks, thus improving visibility.