The National Transportation Safety Board (NTSB) recently identified implementation of positive train control (PTC) among its 2013 "Most Wanted List" of desired safety improvements in the transportation industry.The safety technology aims to prevent deadly train crashes that are caused by human error. So far, railroads have spent more than $1.5 billion in private capital on PTC implementation, which federal law requires railroads to complete by Dec. 31, 2015.Although railroads remain committed to meeting that deadline, unresolved issues and technical challenges are making the timeframe look unrealistic, many industry representatives believe. Whether the industry's concerns will be addressed or resolved in the new Congress remains to be seen.Do you have experience working with PTC at your company or railroad? If so, what are some of the challenges you face in its implementation? Do you think December 2015 is a realistic deadline? Please consider sharing your opinions by answering this week's poll question on ProgressiveRailroading.com, and/or by leaving a comment in response to my post.