This piece from Grist looks at issues of safety and design in multi-use paths.
"[T]here's a disconnect between the speedy reality of bicycle transportation and the slow, recreational uses these trails are designed for. Multi-use paths are only required to be eight feet wide. That's fine for a stroll in the park, but when you factor in two lanes for bikes as well as joggers, skaters, and roving families, it's alarmingly narrow.
Most planning guidelines acknowledge that a 10-foot trail width is better, and recommend 12 for areas with heavy bicycle traffic. Even that -- as we learned on the Katy Trail, which is still being built to these state-of-the-art standards and even includes a narrower, supplemental trail for walking -- isn't enough when bikes are in the mix."