Category talk:616 Temporary Traffic Control
The work zone figure entitled "a typical detour" shows signs numbered 17R, 18, 29 and 52 on sheet 1, but does not define what these signs are. --Martik2 15:57, 28 January 2009 (CST)
Keith L. Smith: Sorry for the delay in answering you. These signs are identified in Fig. 616, Signs and Devices Legend. "17R" is Detour (right), M04-1; "18" is Detour Ahead, WO20-2; "29" is Road Closed, R11-2 and "52" is End Detour, MO4-8a. Someday we will have the technology to improve on this method that relies on using a legend to decode the signs' numbers.
40 mph taper lengths
In the sign spacing and device spacing chart, the taper lengths for 40 and 45 mph are lumped together. The problem with lumping 40 with 45 is that the equation used to determine the taper length changes between 40 and 45 mph. This leads to a much greater difference in taper length than would normally be expected for a 5 mph difference. Although the equations are both shown in the chart, the people using the chart and not equations will be using a 540' taper when only a 320' is needed (12 ft lane). Adding another row to the table for 35-40 mph might be a solution to this issue.
Keith L. Smith: Traffic responds: Thanks the comments are accurate, however, when the table was built they purposely kept to 10 mph ranges vs. every 5 mph. As you noted the difference would be 120' in taper length but only requires two additional channelizes. It would not be a problem to use the calculated length especially if a field condition warranted that. Using a longer taper isn't an issue at all, though. Please remember these taper lengths and all TTC shall be designed to meet the posted speed limit needs vs. the reduced WZ speed.