Ford is launching a car that can read speed limit signs and automatically slow down if needed. It will go on sale in Europe but it might be trickier to make it work in the US.

The S-Max features ‘Intelligent Speed Limiter’, which will let drivers decide whether they want to automatically restrict their speed to the actual limit, or up to 5 mph faster. (It’s also possible to switch it off altogether.)

The feature combines two existing technologies used in Fords (and other cars): a camera with automatic sign recognition, and a variation on cruise control. If the S-Max detects it’s going too fast for the speed limit, it doesn’t apply the brakes, but rather limits the amount of fuel going to the engine, making for a more gradual reduction to the target speed.

There’ll be an audible alert when the slowdown starts, meaning the driver can also ease off on the accelerator. If the driver does push down on the accelerator again, it will override the slowdown, allowing them to overtake or avoid a collision.

Drivers can also choose to have the system use information about speed limits from navigation databases, for example in rural areas where signs may be sparser, less visible, or partially obscured by overgrown plants and trees.

While Ford is considering launches in Asia and the US later on, USA Today notes a key difference that could make it trickier to use the technology in the US. It says that European road signs tend to appear some distance before the point at which the speed limit actually changes, allowing drivers to slow down, while US signs take immediate effect.

Meanwhile ExtremeTech notes a cultural difference: while European traffic officials are more likely to be stringent about enforcing limits and issuing penalties, American drivers may be more likely to believe they have a bigger ‘cushion’ over the limit before they face a serious risk of being penalized.

It also notes that even those drivers who are happy in theory to stick to the limit this way may find themselves frustrated at consistently driving much slower than the surrounding traffic.