Sure, but they're a reaction to "designed for cars to go fast". As a general statement, we do in fact engineer our roadways with maximum travel speed as one of

Sure, but they're a reaction to "designed for cars to go fast". As a general statement, we do in fact engineer our roadways with maximum travel speed as one of, if not the, top factors. And then we design closed-off culdesac neighborhoods to limit our exposure to those fast roads. Where instead we could simply prioritize other transit options and other neighborhood designs (put shopping and schools within walking distance, with appropriate infrastructure).