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Why do cars have top speeds that are insane? – Roadshow

The top speed in the U.S. is 85 MPH on a few roads, and a lot lower on most. Yet many cars are built to hit 155 MPH or more. Why?

Volvo will limit its new cars to 112 MPH starting in 2020 as part of its Vision 2020 initiative. Why 112? That's the conversion from the round number of 180 km/h, still a very stout top speed but a lot lower than the nominal 155 MPH that is the common electronic limit on many new cars today. But wait, there's more.

An increasing number of mainstream carmakers, like Honda, are offering speed limit sign recognition via cameras on their cars that also handle lane marking recognition for lane departure control. 

Aside from a pocket of Texas, you can't even approach three digit speeds legally, let alone the 150+ that many cars are able to achieve.


Citroen goes a step further, letting you press one button on the wheel to automatically set whatever the speed limit the car detected. A few cars in the EU have what is known as Active ISA - Active Intelligent Speed Assist - that automatically sets your car's top speed to match the speed limit unless you override it. By 2022 all new cars sold in the EU will be required to have it. The data that determines local speed limit can be gleaned from a camera, GPS database, or radio beacon.

Not many cars have a speedometer that goes up to 1001 - even if it is km/h. The Bugatti Veyron is an extreme example of the many cars that have too much on tap.


When Level 4 autonomous cars arrive, speed limit tech will graduate to a new era: The end of driver involvement. Self-driving cars should unfailingly - and sometimes infuriatingly - follow speed limits and traffic laws to the letter. 

If you're about to point out how the autobahn "has no speed limits", know that about a third of its 8,000 miles does have a speed limit of 75 or 80 miles per hour and there is a constant drumbeat of proposals to put limits on the rest, though that idea is on ice for now.

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