It's entirely impractical to expect NY to build collision barriers at every spot where pedestrians get near cars within the city. Unless you want to have raised / underground pedestrian crossings everywhere (which have generally not been found to work very well, and are ugly as hell too), the reality is you're going to have traffic and pedestrians intermixed within the city.

"The goal of improving roads is to increase the throughput of traffic" - that is considered an outdated goal by most planners these days. For one thing, if you increase the capacity of roads, you simply encourage more driving, and things end up congested anyway. In many cases urban planners now actively seek to decrease the throughput of traffic on mixed-use streets in urban areas.