Urban Cycling Safety Innovations Portland, Oregon is one of several U.S. cities with a progressive bicycling culture. A couple of innovations the city has implemented are "bike boxes" and "sharrows". 

Bike boxes are road markings that designate exactly where cyclists and motorists should place their vehicles when stopped at an intersection with a red light. The main idea is to prevent the notorious "right hook" as a cause of collisions. The jury is still out in terms of effectiveness, but bike boxes are receiving mostly positive reviews so far. (On wikipedia these are called Advanced Stop Lines and around here they're called "green boxes".)

Sharrows are shared lane road markings on roads/lanes shared by cyclists and motor vehicles. In Portland, they are found on city designated bike routes without bike lanes. The idea being that it's a visual cue to cyclists and motorists that the lane is to be shared. 

Question: What are other infrastructure modifications a community can make to enhance bicycling safety?
Bike Loops (sensors for traffic lights)

One thing we have in the SF bay area are markings on the road where a bike can stand to trigger a green light.  In intersections where the lights are governed by sensors, bikes can't usually trigger those, and end up having to either run the light, push the pedestrian crossing button, or wait for a car to show up.  With these markings, cyclists can know where a more sensitive sensor is places that is more likely to trigger the light.