Convenient, yes. Free of consequences, no. Here's what's actually happening to your clear coat every time it goes through the tunnel.
Automatic car washes exist because they're fast and cheap, not because they're gentle. Understanding what's actually touching your paint helps explain why cars washed exclusively at automatic locations tend to show more swirl marks and dulling over time than cars washed by hand or with a touchless system.
Soft-touch brush washes use fabric strips or foam that brush across your car — and across every other car that went through before yours. Those brushes pick up grit, sand, and road debris from previous vehicles and drag it across your paint on the next pass. That's the direct cause of the fine spiderweb scratches known as swirl marks, which become especially visible in direct sunlight or under a streetlight at night.
Touchless washes rely on high-pressure water and stronger detergents instead of physical contact, which avoids the scratching problem. The trade-off is that the detergents used are often more aggressive to compensate for the lack of physical agitation, which can strip wax or sealant faster than a gentler hand wash would. It's the safer of the two automatic options, but it's still not neutral for a coated or waxed finish.
It's rarely one wash that causes visible damage — it's the accumulation. Each pass through a brush wash adds a small number of fine scratches; over months of weekly washing, those scratches compound into the hazy, dull look many daily-driven cars develop, even ones that are washed regularly. Owners are often confused why a car that's 'always washed' still looks tired — the washing itself is often the cause.
The condition of the paint underneath matters as much as the wash method. A properly maintained ceramic coating creates a slicker, harder surface that's more resistant to the fine scratching that causes swirl marks — dirt and grit have less to grip onto, and the coating itself is significantly harder than bare clear coat. It won't make an automatic wash risk-free, but it meaningfully reduces the damage each pass causes.
If minimizing paint damage matters to you, here's the order of preference.
Arête