That looks like a small lip, not a curb; which would explain why people are flailing.

I think we can judge how high the curb is by the light coming in from the right hand side, and the length of the shadow. I don't have the patience for the mathematics.

The US has a government entity that delegates a template to how curbs should be designed; specifically ramps. Which is exactly what is happening here. That curb is at a grade from the ramp; which is about level with the street or road. It doesn't take a scientist to realize that there is a problem at this section of road and ramp. The question is how to fix it? Is it cheaper to train the population to watch their fucking step? No it would be cheaper to put a sign in place that says, "What your fucking step," with a big fucking index finger pointing to the curb.

http://www.fhwa.dot.gov/environment/sidewalk2/sidewalks207.htm

Curb ramps provide access for people who use wheelchairs, who would otherwise be excluded from the sidewalk because of the barrier created by the curb. However, curb ramps can create major information barriers for people with vision impairments who rely on the curb to identify the transition point between the sidewalk and the street. The following section evaluates the impact of curb ramps on these two user groups and provides design strategies to enhance the benefits of curb ramps for people with mobility impairments while minimizing the drawbacks for people with vision impairments.

And in a quadruple blind experiment, the test subjects, testers, and statisticians are all vision impaired.