The TTC zone includes the entire section of roadway between the first advance warning sign through the last traffic control device, where traffic returns to its normal path and conditions. Most TTC zones can be divided into four areas: the advance warning area, the transition area, the activity area, and the termination area. Figure 2 illustrates these four areas.
A. ADVANCE WARNING AREA
In the advance warning area, drivers are informed of what to expect. The advance warning may vary from a single sign or flashing lights on a vehicle to a series of signs in advance of the TTC zone transition area.
The number and spacing of advance warning devices is dependent on the type of activity in the work zone, the speed and volume of traffic and the visibility of the work zone to approaching traffic. Where construction is in or near a hill or horizontal curve, the advance warning area shall be extended so that there is adequate sight distance of the TTC zone.
Advance warning is normally not needed when the activity is sufficiently removed from the driver's path such that it does not interfere with traffic flow.
B. TRANSITION AREA
When reduction of the driver's normal path is required, traffic must be channelized from the normal path to a new path. This redirection is intended to occur at the beginning of the transition area. In mobile operations, this transition area moves with the workspace. Transition areas usually involve strategic use of tapers, which are discussed in detail in Section 13. The length of the transition area is dependent on the speed of approaching traffic and the lateral distance which traffic is being diverted.
C. ACTIVITY AREA
The workspace is that portion of the roadway closed to traffic and set aside for workers, equipment, and materials. Long-term workspaces should be delineated by pavement markings and by channelizing devices or may be shielded by barriers to exclude vehicular, pedestrian, and bicycle traffic.
(See Figure 2 - Temporary Traffic Control Zones)
The buffer space separates the traffic area from the work activity and provides recovery space for an errant vehicle. Buffer spaces may also be used to separate opposing traffic flows (Figure 3) or to separate pedestrian traffic areas from vehicular traffic areas. Neither work activity nor storage of equipment, vehicles, or materials shall occur in this space.
Except where space limitations prohibit it, a longitudinal buffer shall be placed in the initial portion of a closed lane in advance of the workspace, as shown in figure 2. Where construction is in or near a hill or horizontal curve, the standard buffer space should be extended so that there is adequate sight distance of the advance warning area and the transition area.
A lateral buffer space shall be used to separate the traffic space from the work space, as shown in figure 2, or a potentially hazardous area, such as an excavation or pavement drop-off. The width of the lateral buffer space should be determined by engineering judgment; however, a minimum lateral buffer space of 2 feet is required between the workspace and the nearest travel lane. Appropriate channelizing devices, such as cones or drums, may be placed inside the lateral buffer space.
D. TERMINATION AREA
The termination area is used to return traffic to the normal traffic path. The termination area extends from the downstream end of the work area to the "END ROAD WORK" signs, if used.