Trail Design and Resources
AASHTO Guide for the Development of Bicycle Facilities 4th Edition, Chapter 5 (2012)
AASHTO provides the gold-standard for traffic engineer design guidelines. Chapter 5 considers shared use paths specifically. AASHTO's recommendations are often conservative and infrequently updated. Because of this, particularly regarding bicycle and pedestrian best practices that are rapidly emerging (see references below), FHWA strongly recommends design flexibility. Because of copyright protections, we cannot post this reference online.
America's Rails-with-Trails 2013
This is the Rails to Trails Conservancy 20 year study of rails-with-trails projects (shared use paths adjacent to active railroad tracks). The exemplary safety record of these facilities, and their community benefits, are pertinent Little Rock's section of the proposed Southwest Trail.
Rails-with-Trails: Lessons Learned 2002
This is US DOT's report of rails-with-trails. It concludes that "it is clear that well-designed RWTs can bring numerous benefits to communities and railroads alike."