[carapace]

If it helps, it's the result of a deliberate domestic propaganda campaign. I usually point to "The Real Reason Jaywalking Is A Crime" (Adam Ruins Everything) https://www.youtube.com/watch?v=vxopfjXkArM for the story.

We can see what traffic was like just as motorized carriages began to mix with pedestrians and horses. Here is "San Francisco, a Trip down Market Street, April 14, 1906" upscaled and colorized: https://www.youtube.com/watch?v=VO_1AdYRGW8

You can see that, at low speeds and modest density, carriages and pedestrians flow together just fine. Although I'm sure there were still lots of accidents, everyone is more-or-less sharing the space. You can already see the problem brewing: horseless carriages can accelerate much faster than horse-drawn carriages.