[Retric]

20+MPH accidents are dangerous on bicycles and they are also more likely to hit pedestrians due to reduced reaction times.

[nerdshoe]

Now we're getting somewhere. Given that these factors are multiplied with automobiles, shouldn't all vehicle speeds be limited so? I am a firm believer that everything should be limited to 30km/h in urban and residential environments where pedestrian and vehicle traffic coexist.

[tetromino_]

> Given that these factors are multiplied with automobiles

Not a given. At speed, cars handle more securely than bicycles; cars have power brakes, ABS, traction control; modern cars often have automatic collision avoidance systems.

[bryanlarsen]

Even automatic collision avoidance systems don't help if a kid chasing a ball jumps out from between two parked cars right in front of your car.

30KPH car-pedestrian collisions are >> 95% survivable. The fatality rate drops dramatically above that speed. Dropping speed limits to 30Kph in areas with shared infrastructure and strictly enforcing them can drop pedestrian fatality rates all the way to zero:

http://www.visionzeroinitiative.com/

[Retric]

Skyways seem like a better alternative as you increases throughput for both pedestrians and cars.

https://en.wikipedia.org/wiki/Skyway EX: https://en.wikipedia.org/wiki/%2B15

Alternatively, you one or both can go underground. (https://en.wikipedia.org/wiki/Underground_city#United_States) Crystal City VA for example has a huge underground mall that almost completely removes pedestrian tragic outside and connects to the subway system. Sadly, it's not a strait path, but there are ~50 buildings connected and it becomes really useful if you live and or work in the area. (http://www.thecrystalcityshops.com/_files/docs/cc-shops-2014...)

[bryanlarsen]

If we had to lower the speed limit to 30kph wherever cars & pedestrians interacted (aka all streets), then magically there would appear money to build separated pedestrian infrastructure like skyways so that politicians could drive faster than 30kph on their routes.