The duration of the work zone is a major factor in determining the number and types of devices used in TTC zones. The five categories of work duration are as follows:
Long-term stationary - Work that occupies a location continuously, day and overnight, for more than 3 days.
Intermediate-term stationary - Work that occupies a location continuously more than one day and overnight, up to 3 days; or night work.
Short-term stationary - Active work zone that occupies a location from 1 hour to 1 day.
Short-duration - Active work zone that occupies a location for up to 1 hour.
Mobile - Work that moves intermittently or continuously.
At LONG- TERM STATIONARY
work zones, there is ample time to install and realize benefits from the full range of traffic control procedures and devices that are available for use. Since these types of work zones extend overnight, all traffic control devices used shall be made with retro- reflective material. Drums shall be used to channelize vehicular traffic. Drums or approved barrier shall be used to separate the activity space from the traffic space. Portable channelizing devices (drums, cones, etc.) shall not be sufficient to separate opposing flows of traffic. Appropriate temporary pavement markings shall be installed and all conflicting pavement markings shall be removed. High-Level warning devices such as changeable message signs or flashing arrow panels should be used whenever possible.
During INTERMEDIATE- TERM STATIONARY work, it may not be feasible or practical to use procedures or devices that are desirable for long-term stationary work zones, such as altered pavement markings, barriers, or changeable message signs. The increased time to place and remove these devices in some cases could significantly lengthen the project, thus increasing exposure time. Since these projects extend overnight, all traffic control devices used shall be made with retro-reflective material. Cones may be used in lieu of drums but must be 28 inches high with white retro-reflective bands when workers are present. Drums or tubular markers affixed to the pavement shall be used if the site is left unattended and traffic is being diverted across conflicting pavement markings or if channelization devices are to be used in lieu of double yellow centerline to separate opposing traffic flows.
Most maintenance and utility operations are SHORT-TERM STATIONARY. The work crew is present to maintain and monitor the TTC zone. A TTC zone in compliance with the figures of this handbook is required; however, for daylight only operations, the traffic control devices used do not need to be made of retro-reflective material. For nighttime operations, the traffic control devices shall either be made of retro-reflective materials or shall be externally illuminated.
Work zones that continue longer than one day, but are abandoned and cleared such that all travel lanes and shoulders are open during periods of inactivity, can be considered as short-term stationary work zones. In such cases, all TTC devices shall be removed or covered during periods of inactivity.
For SHORT-DURATION activities, it generally takes longer to set up and remove the TTC zone than to perform the work. Typically, such operations can be accomplished in 60 minutes or less. There are hazards involved for the crew in setting up and taking down a traffic control zone. Also, as the work time is short, the time during which motorists are affected is significantly increased when additional devices are installed and removed. Considering these factors, it is generally held that simplified control procedures are warranted for short-duration projects. Such shortcomings may be offset by the use of other, more dominant devices, such as high intensity rotating, flashing, oscillating, or strobe vehicles or larger, more visible signs.
The trade-off is economical because work duration is short. Mobility is essential; the crew is always on site. Safety is not compromised, as numerous small devices are merely replaced by fewer, more dominant and effective devices.
MOBILE operations include activities that stop intermittently and then move on (e.g., pothole patching) and those that move continuously (e.g., pavement striping). With operations that move slowly (less than 3 mph), it may be feasible to use stationary signing that is periodically retrieved and repositioned in the advance warning area. At higher speeds, trucks are typically used as components of the traffic control zones. Appropriately colored and marked vehicles with signs, high intensity rotating, flashing, oscillating, or strobes, truck mounted attenuators, and special lighting panels move as part of a train behind the work vehicles.
Mobile operations that move at speeds greater than 20 mph, such as snowplowing operations, shall have appropriate devices on the equipment, (i.e., rotating lights, signs, or special lighting), or shall use a protection vehicle with appropriate warning devices.
Safety should not be compromised by using fewer devices simply because the operation will frequently change its location. Portable devices should be used. Flaggers may be used, but caution must be exercised so they are not exposed to unnecessary hazards. The control devices should be moved periodically to keep them near the work area. If mobile operations are in effect in a travel lane of a high-speed (45 mph or greater), multi-lane roadway, flashing arrow panels mounted on the back of each vehicle should be used.