A study of 13 road safety measures in New York City installed between 1998 and 2008 found that road diets (reducing travel lanes and adding bike lanes) reduced crashes by 67%. High-visibility crosswalks reduced pedestrian crashes by 48%. Speed humps and reduced speed limits were found to have a limited impact on crashes.
Chen, Li, Cynthia Chen, Reid Ewing, Claire E. McKnight, Raghavan Srinivasan, and Matthew Roe. (2013). Safety countermeasures and crash reduction in New York City—Experience and lessons learned. Accident Analysis & Prevention, 50, 312-322.