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6G. TYPES OF TEMPORARY TRAFFIC CONTROL ZONE ACTIVITIES

Each traffic control zone is different. Many variables, such as location of work, road type, speed, volume, geometrics, vertical and horizontal alignment, pedestrians, and intersections affect t needs of each zone. The goal of traffic control in work areas is safety with minimum disruption to traffic, and the key factor in making the temporary traffic control zone safe and efficient is proper judgment.

Bicyclists also need protection and access to the roadway. a bicycle path is closed because of work in progress, a signed alternate route should be provided. Bicyclists should not be directed onto the same path used by pedestrians. For more detail on controlling bicycle traffic, see part IX of the MUTCD.

Utility work takes place both within the roadway and outside the shoulder, to construct and maintain the hardware and equipment used to provide power, light, water, gas, and telephone service. Utility operations are generally short daytime operations, except under emergency conditions. Often they are performed on low-volume, low-speed streets. Operations often involve intersection as that is where many of the network junctions occur. The crew size is usually small, only a few vehicles are involved, and the number and types of traffic control devices placed in the temporary traffic control zone may be minimal. As discussed in section 6G- 20a.(4), however, the reduced number of devices in this situation should be offset by the use of high-visibility devices, such as special lighting units on work vehicles. Figures TA-6, TA-10, TA-15, TA-18, TA-21, TA-22, TA-23, TA-26 and TA-33 are examples of typical applications for utility operations. Other typicals may apply as well.

In this section, typical temporary traffic control zone situations are organized according to duration and location of work and highway type. Section 6H, which follows the same organization, presents layouts of these typical temporary traffic control zone situations. Table VI-4 in section 6H indexes by figure number the typical temporary traffic control zone applications described in this section.

6G-1. TYPICAL APPLICATIONS

Typical applications include a variety of traffic control methods, but do not include a layout for every conceivable work situation. Typical applications should be altered, when necessary, to fit the conditions of a particular temporary traffic control zone. Standards presented in sections 6A-6F should be given priority over the examples given in the typical applications.

The typical applications illustrated in section 6H generally represent highway agency norms. Other devices may be added to supplement the devices shown in the typical applications, and sign spacings and taper lengths may be increased to provide additional time or space for driver response. In some situations, however, such as an urban setting, too many devices can spread signing over too long a distance to be meaningful. When conditions are not as difficult as those depicted in the typical application, fewer devices may suffice.

Although portable barriers are frequently indicated in the typical applications of section 6H, they are not traffic control devices in themselves. However, when placed in a position identical to a line of channelizing devices and marked and/or equipped with appropriate channelizing features to give guidance and warning both day and night, they serve as traffic control devices and, therefore, must conform to all requirements for such devices set forth throughout part VI.

6G-2. SELECTING THE TYPICAL APPLICATION

Selecting the most appropriate typical application and modifications for a temporary traffic control zone requires knowledge and understanding of that zone. Although there are many ways of categorizing temporary traffic control zone applications, the three factors mentioned earlier (work duration, work location, and highway type) have been used to characterize the typicals illustrated in section 6H.

  1. Duration of Work

    Work duration is a major factor in determining the number and types of devices used in temporary traffic control zones. The five categories of work duration and their time at a location are as follows:
  • Long-term stationary-Work that occupies a location more than 3 days.
  • Intermediate-term stationary-Work that occupies a location from overnight to 3 days.
  • Short-term stationary-daytime work that occupies a location from 1 to 12 hours.
  • Short, Duration-Work that occupies a location up to 1 hour.
  • Mobile-Work that moves intermittently or continuously.

    (1) Long-Term Stationary
    At long-term stationary temporary traffic control 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. Generally, larger channelizing devices are used, as the have more retroreflective material and offer better nighttime visibility. The larger devices are also less likely to be displaced or tipped over-an important consideration during those periods when the work crew is not present. Furthermore, as long- term operations extend into nighttime, retroreflective and/or illuminated devices are required. Temporary roadways and barrier can be provided, and inappropriate markings should be removed and replaced with temporary markings.
    (2) Intermediate-Term Stationary
    During intermediate-term stationary work, it may not be feasible or practical to use procedures or devices that would be desirable for long-term stationary temporary traffic control zone such as altered pavement markings, barriers, and temporary roadways. The increased time to place and remove these devices i some cases could significantly lengthen the project, thus increasing exposure time. In other instances, there might be insufficient payback time to make more elaborate traffic control economically attractive.
    (3) Short-Term Stationary
    Most maintenance and utility operations are short-term stationary work. The work crew is present to maintain and monitor the temporary traffic control zone. The use of flagger is an option. Lighting and/or retroreflective devices should be chosen to accommodate varying seasonal, climatic, and visibility situations.
    (4) Short Duration
    During short-duration work, there are hazards involved for the crew in setting up and taking down the traffic controls. Also, since the work time is short, the time during which motorists are affected is significantly increased as the traffic control is expanded. Considering these factors, it is generally held that simplified control procedures may be warranted for short-duration work. Such shortcomings may be offset by the use of other, more dominant devices such as special lighting units on work vehicles.
    (5) Mobile
    Mobile operations are work activities that move along the road either intermittently or continuously. Mobile operations often involve frequent short stops, each as much as 15 minutes long, for activities such as litter cleanup, pothole patching, or utility operations and are similar to stationary operations. Warning signs, flashing vehicle lights, flags, and/or channelizing devices should be used.

    Mobile operations also include work activities in which workers and equipment move along the road without stopping, usually at slow speeds. The advance warning area moves with the work area. Traffic should be directed to pass safely. Parking may be prohibited, and work should be scheduled during off-peak hours. For some continuously moving operations-such as street sweeping - where volumes are light and visibility is good, a well-marked and well-signed vehicle may suffice. If volumes and/or speeds are higher, a shadow or backup vehicle equipped as a sign truck, preferably supplied with a flashing arrow display, should follow the work vehicle. Where feasible, warning signs should be placed along the roadway and moved periodically as the work progresses. In addition, vehicles may be equipped with such devices as flags, flashing vehicle lights, truck-mounted attenuators, and appropriate signs. These devices may be required individually or in various combinations, including all of them, including all of them, as determined necessary.

    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 on a high-speed travel lane of a multilane divided highway, flashing arrow displays should be used.
  1. Location of Work

    The choice of traffic control needed for a temporary traffic control zone depends upon where the work is located. As a general rule, the closer the work is to traffic, the more control devices are needed.

    Work can take place in the following locations:
    (1) Outside of the shoulder edge. Devices may not be needed if work is confined to an area 15 or more feet from the edge of the shoulder. Consideration should be given to roadway characteristics, roadway geometrics, and vehicle speed. A general warning sign like ROAD MACHINERY AHEAD should be used if workers and equipment must occasionally move closer to the highway.

    (2) On or near the shoulder edge. The shoulder should be signed as if work were on the road itself, since it is part of the drivers' "recovery area." Advance warning signs are needed. Channelizing devices are used to close the shoulder, direct traffic, and keep the work space visible to the motorist. Portable barriers may be needed to prevent encroachment of errant vehicles into the work space and to protect workers.

    (3) On the median of a divided highway. Work in the median may require traffic control for both directions of traffic, through the use of advance warning signs and channelization devices. If the median is narrow, with a significant chance for vehicle intrusion into long-term work sites and/or crossover accidents, portable barriers should be used.

    (4) On the traveled way. Work on the traveled way demands optimum protection for workers and maximum advance warning for drivers. Advance warning must provide a general message that what is taking place, information about specific hazards, and actions the driver must take to drive through the temporary traffic control zone.
  2. Roadway Type

    Roadway type is also a primary factor in the use of temporary traffic control zone traffic control devices. Typical application diagrams of the following categories of roadway type are included in section 6H:

    (1) Rural Two-lane Roadways

    (2) Urban Arterial Roads

    (3) Other Urban Streets

    (4) Rural or Urban Multilane Divided and Undivided Highways

    (5) Intersections

    (6) Freeways

    Rural two-lane roadways are characterized by relatively low volumes and high speeds. Urban arterial roads often have lower speeds, but they may require significant controls because of higher traffic volumes and closer spacing of such design features as intersections. Other urban streets with light traffic volumes will generally require fewer but more closely spaced devices. Major arterial and freeways need the highest type of traffic control, primarily because of high speeds and often high volumes of traffic.

    To improve safety, typical designs may be modified to a more elaborate treatment, as indicated by the following:
  • Additional devices

    - Additional signs
    - Flashing arrow displays
    - More channelizing devices at closer spacing
    - Temporary raised pavement markers
    - High-level warning devices
    - Portable changeable message signs
    - Portable traffic signals - Portable barriers
    - Impact attenuators - Screens
    - Rumble strips

  • Upgrading of devices

    - A full complement of standard pavement markings in areas of high hazard
    - Brighter and/or wider pavement markings
    - Larger signs
    - Higher type channelizing devices
    - Barriers in place of channelizing devices

  • Improved geometrics at detours or crossovers,
    giving particular attention to the provisions set forth in section 6B

  • Increased distances

    - Longer advance warning area
    - Longer tapers

  • Lighting

    - Temporary roadway lighting
    - Steady-burn lights used with channelizing devices
    - Flashing lights for isolated hazards
    - Illuminated signs
    - Floodlights

    When conditions are not as difficult as those depicted in the typical applications, fewer devices may suffice. However, uniformity of devices and their application is always extremely important.

6G-3. WORK OUTSIDE THE SHOULDER

Traffic control depends primarily on devices such as advance warning signs, flashing vehicle lights, and flags. An advance warning sign should be used when any of the following conditions occur:

  • Work will be performed immediately adjacent to the shoulder at certain stages of the activity.
  • Equipment may be moved along or across the highway.
  • Motorists may be distracted by the work activity.

A typical sign for this situation may be ROAD WORK AHEAD. If the equipment travels on or crosses the roadway, it should be equipped with appropriate flags, flashing lights, and/or a SLOW MOVING VEHICLE symbol. A typical layout for stationary work outside of the shoulder is shown in figure TA-1. Special signing for a blasting zone is shown in figure TA-2. A typical layout for short-duration, mobile and moving work outside of the shoulder and on the shoulder is shown in figure TA-4.

6G-4. WORK ON THE SHOULDER

This section describes typical applications that cover shoulder work. It is divided into shoulder work that does and does not interfere with traffic.

  1. No Encroachment on Traveled Way

    There is no direct interference with traffic. When the shoulder is occupied or closed, the drivers should be advised and the workers should be protected. In some instances, this may require the use of portable barriers if work is directly adjacent to the travel lane. Usually, the single warning sign, SHOULDER WORK, is adequate. When an improved shoulder is closed on a high- speed roadway, it should be treated as a closing of a portion of the road system because drivers expect to be able to use it in emergencies. Motorists should be given ample advance warning that shoulders are closed to use as refuge areas throughout a specific length of the approaching temporary traffic control zone. The signs should read SHOULDER CLOSED with distances indicated. The work space on the shoulder should be closed off by a taper of channelizing devices with a length of 1/3 L, using the formulas in section 6C-3. Flashing arrow displays should be used only in the caution mode.

  2. Minor Encroachment on Traveled Way

    When work is on the shoulder or takes up part of a lane, traffic volumes, vehicle mix (buses, trucks, and cars), speed, and capacity should be analyzed to determine whether the affected lane should be closed. The lane encroachment should permit a remaining lane width of 10 feet or the lane should be closed. However, 9 feet is acceptable for short-term use on low-volume, low-speed roadways for traffic that does not include longer and wider heavy commercial vehicles. Figure TA-6 illustrates a method for handling traffic where the stationary or short duration work space encroaches slightly into the traveled way.

6G-5. WORK WITHIN TRAVELED WAY-RURAL TWO-LANE

  1. Detours

    Typical layouts for detours of two-lane highways are shown in figures TA-7, TA-8, and TA-9. Figure TA-7 illustrates the controls around an area where a section of roadway has been closed and a bypass constructed. Channelizing devices and pavement markings are used to indicate the transition to the temporary roadway.

    Detour signing is usually handled by the traffic engineer with authority over the roadway because it is considered a traffic routing problem. Detour signs are used to direct traffic onto another roadway. When the detour is long, signs should be installed to periodically remind and reassure drivers that they are still on a detour. This is done by using the DETOUR MARKER (M4-8) or DETOUR (M4-9) signs.

    When an entire roadway is closed, as illustrated in figure TA-8, a detour should be provided and traffic should be warned in advance of the closure. This illustration is an example for a closing 10 miles from the intersection. If local traffic is allowed to use the roadway up to the closure, the ROAD CLOSED TO THRU TRAFFIC sign should be used. The portion of the road open to local traffic should have adequate signing, marking, and protection.

    Detours should be signed so that traffic will be able to get through the entire area and back to the original roadway as shown in figure TA-9.

  2. One-Way Traffic Control

    When one lane is closed on two-lane, two-way roads, the remaining lane must be used by traffic traveling in both directions. Techniques for controlling traffic under such conditions are described in section 6C-5.

6G-6. WORK WITHIN TRAVELED WAY-URBAN STREETS OR ARTERIAL

Urban temporary traffic control zones may be divided into segments. Decisions must be reached as to how to control vehicular traffic, how many lanes are required, or whether any turns should be prohibited at intersections. Pedestrian traffic must be considered. If work will be done on the sidewalk, will it be necessary to close the sidewalk and assign the pedestrians to another path? Next, decisions must be reached as to how to maintain access to business, industrial, and residential areas. Even if the road is closed to vehicles, pedestrian access and walkways must be provided.

Bicyclists' protection and access are especially needed on these types of roadways. If a bicycle path is closed because of the work being done, a signed alternate route should be provided. Bicyclists should not be directed onto the path used by pedestrians. For more details on controlling bicycle traffic, see part IX of the MUTCD.

Utility work takes place both within the roadway and outside the shoulder to construct and maintain the hardware and equipment used to provide power, light, water, gas, or telephone service. Utility operations are generally short daytime operations, except under emergency conditions. Often they are performed in low-volume and low-speed streets. operations often involve intersections, since that is where many of the network junctions occur. The crew size is usually small, only a few vehicles are involved, and the number and types of traffic control devices placed in the temporary traffic control zone may be minimal. As discussed in section 6G-2.a.(4), however, in this situation the reduced number of devices should be offset by the use of high-visibility devices, such as special lighting units on work vehicles. Figures TA-6, TA-10, TA-15, TA-18, TA-21, TA-22, TA-23, TA-26, and TA-33 are examples of typical applications for utility operations. other typicals may apply as well.

6G-7. WORK WITHIN TRAVELED WAY-RURAL OR URBAN, MULTILANE DIVIDED AND UNDIVIDED, NONACCESS CONTROLLED

This section describes typical applications for work on multilane (four or more) streets or highways. It is divided into right lane closures, left lane closures, multiple-lane closures, and closures on five-lane roadways.

Figure TA-34 illustrates a lane closing in which portable concrete barriers are used. As described in section 6F-8, portable barriers are not in themselves traffic control devices but, if placed along an adequate taper, transition, or tangent section, they may serve as traffic control devices to provide guidance and warning to passing traffic. In serving this traffic control function, portable barriers must be equipped with appropriate channelizing devices, delineation, and/or other traffic control devices in order to perform acceptably during day and night operations. When determined necessary by an engineering analysis, barriers should be used for added safety to prevent incursions of errant vehicles beyond their designated travel lanes. The four primary functions of barriers are as follows:

  • To keep traffic from entering work areas, such as excavations or material storage sites.
  • To provide protection for workers and pedestrians.
  • To separate two-way traffic.
  • To protect roadwork such as false work for bridges and other exposed objects.
  1. Right Lane Closed

    Traffic control similar to that shown in figure TA-33 may be used for undivided or divided four-lane roads. If traffic volumes are high, traffic may back up. If morning and evening peak hourly traffic volumes in the two directions are uneven and the greater volume is on the side where the work is being done, the inside lane for opposing traffic may be closed and made available to the side with heavier traffic, as shown in figure TA-31. A volume check in both directions should be made before this method is used.

    If the heavier traffic changes to the opposite direction, the traffic control can be changed to allow two lanes for opposing traffic by moving the devices from the opposing lane back to the centerline. If these changes occur frequently, cones or tubes should be used at close spacing to emphasize the centerline.

  2. Left Lane Closed

    If the work activity can be contained entirely within the left (or inside) lane, it may be appropriate to close only that lane. Channelizing devices should be placed along the centerline and outside of the work activity to give advance warning to the opposing traffic. An alternative is to close the two center lanes, as shown in figure TA-30, to give motorists and workers additional protection and to provide easier access to the work space. Overall safety needs, evaluated on the basis of existing traffic volumes and speeds in each direction, is the main factor for determining alternatives.

  3. Multiple Lanes Closed

    When the work occupies multiple lanes for one direction of traffic, the number of lanes remaining open may be reduced to one for each direction as shown in figure TA-32. A capacity analysis is necessary before this method is initiated. Traffic should be moved over one lane at a time and the tapers should be separated a distance of 2L, as shown in figure TA-37. When both center lanes are closed, traffic controls may be used as indicated in figure TA-30. When a roadway must be closed on a divided highway, a median crossover may be used [see section 6G-9(b) and (c)]. When the directional roadway is closed, inapplicable WRONG WAY signs a markings, and other existing traffic control devices at intersections within the temporary two-lane, two-way operations section, should be covered, removed, or obliterated.

  4. Five-Lane Roads

    Traffic control for lane closures on five-lane urban or rural roads is similar to other multilane undivided roads. Figures TA-32 and TA-34 should be adapted for use on five-lane roads.

    For short-duration and mobile operations, see figure TA-35.

6G-8. WORK WITHIN TRAVELED WAY-INTERSECTIONS

For work at an intersection, advance warning signs, devices, and markings are to be used as appropriate on all cross streets. The effect of the work upon signal operation should be considered such as signal phasing for adequate capacity and for maintaining adjusting detectors in the pavement.

A shoulder closing is done as shown in figure TA-4. A minor encroachment is done as shown in figure TA-6.

When a lane is closed on the approach side of an intersection standard lane closure and taper techniques apply, as shown in figure TA-21. A turn lane may be used for through traffic.

When a lane must be closed on the far side of an intersection that lane should be closed on the near side approach, or converted to an exclusive turn lane, as shown in figures TA-22, TA-23, TA-24 and TA-25.

If the work is within the intersection, several options exist as follows:

  • Keep the work space small so that traffic can move around it, as shown in figure TA-26
  • Use flaggers to assign the right-of-way, as shown in figure TA-27.
  • Do the work in stages so the work space is kept small.
  • Reduce traffic volumes by road closing or upstream diversions.

6G-9. WORK WITHIN TRAVELED WAY-FREEWAYS

Serious problems of traffic control occur under the special conditions encountered where traffic must be moved through or around temporary traffic control zones on high-speed, high-volume roadways. Although the general principles outlined in the previous sections of the manual are applicable to all types of highways, special consideration should be given to modern, high-speed, access-controlled highways to accommodate traffic in a safe and efficient manner that also adequately protects work forces. The density of traffic on these facilities requires that the most careful traffic control procedures be implemented, such as inducing critical merging maneuvers well in advance of work spaces and in a manner that creates minimum turbulence and delay in the traffic stream. These situations may require more conspicuous devices than specified for normal rural or urban street use. However, the same important basic considerations of uniformity and standardization of general principles apply for all roadways.

The year-round, night-and-day intensity of use of expressways and freeways means that there is no season during which work can be scheduled when traffic volumes and density are low. These activities therefore must be performed under extremely heavy traffic conditions.

Traffic controls for short-duration and mobile operations are shown in figure TA-35.

  1. Problem Areas

    The performance of work under high-speed, high-density traffic on controlled access highways is complicated by many of the design and operational features inherent to their use.

    The presence of median dividers that establish separate roadways for directional traffic may also prohibit the closing of that roadway or the diverting of traffic to other lanes. A typical layout for shifting traffic lanes around a work space is shown in figure TA-36.

    Lack of access to and from adjacent roadways prohibits rerouting of traffic away from the work space in many cases.

    A major consideration in the establishment of traffic control is the vehicular speed differential which exists and the limited time available for drivers to react safely to unusual conditions while still providing an activity area that protects workers. Traffic control for a typical lane closure is shown in figure TA-33. Traffic control for multiple and center lane closings is shown in figures TA-37 and TA-38. Figure TA-37 is the preferred method for closing a center lane when the open lanes have the capacity to carry traffic.

    Other conditions exist where work must be limited to night hours, thereby necessitating increased use of warning lights, illumination of work spaces, and advance warning systems.

  2. Two-Lane, Two-Way Traffic on One Roadway of a Normally Divided Highway

    Two-lane, two-way operations (TLTWO) on one roadway of a normally divided highway is a typical application that requires special consideration in the planning, design, and construction phases. As unique operational problems (for example, increasing the risk of serious head-on collisions) can arise with the TLTWO, this typical application will be discussed here.

    Before including a TLTWO in the traffic control plan for a project, careful consideration should be given to its appropriateness. The following items should be considered during the decision-making process:
  • Is a suitable detour available?
  • What are the characteristics of the traffic?
  • Can traffic be maintained on the shoulder?
  • Can temporary lanes be constructed in the median?
  • Can the work be accomplished by closing only one directional lane? If this option is selected for consideration, will it result in additional hazard to temporary traffic control zone personnel?
  • If a TLTWO is selected, will this result in a shorter contract time?
  • Will the TLTWO allow a contractor to perform the work more efficiently and thus result in a substantial decrease in contract cost?
  • What is the "track record" of similar installations?
  • Are there any width or height restrictions that would preclude the TLTWO or the use of a shoulder or the median as a temporary lane?
  • What are the condition of the pavement and the shoulders in the proposed TLTWO section? Due to width restriction, traffic may drive on the shoulders, which must be structurally adequate.

The traffic control plan as shown in figure TA-39 shall include provision for separate opposing traffic whenever two-way traffic must be maintained on one roadway of a normally divided highway. The TLTWO shall be used only after careful consideration of other available methods of traffic control.

When traffic control must be maintained on one roadway of a normally divided highway, opposing traffic shall be separated either with portable barriers (concrete safety-shape or approved alternate), or with channelizing devices throughout the length of the two-way operation. The use of striping, raised pavement markers, and complementary signing, either alone or in combination is not considered acceptable for separation purposes.

Treatments for entrance and exit ramps within the two-way roadway segment of this type of work are shown in figures TA-40 and TA-41.

  1. Crossovers

The following are good guiding principles for the design of crossovers:

  • Tapers for lane drops should not be contiguous with crossovers.
  • Crossovers should be designed for speeds not less than 10 miles per hour below the posted speed, the off-peak 85th percentile speed prior to work starting, or the anticipated operating speed of the roadway, unless unusual site conditions require that a lower design speed be used.
  • A full array of channelizing devices, delineators, and full-length, properly placed pavement markings are important in providing drivers with a clearly defined travel path.
  • Portable concrete barriers and the excessive use of traffic control devices cannot compensate for poor geometric design of crossovers.
  • The design of the crossover should accommodate all roadway traffic including trucks and buses.
  • A clear area should be provided adjacent to the crossover.
  1. Interchanges

    Access to interchange ramps on limited access highways should be maintained even if the work space is in the lane adjacent to the ramps. If access is not possible, ramps may be closed by using signs and Type III barricades. Early coordination with officials having jurisdiction over the affected cross streets is needed before ramp closings.

    Egress to exit ramps should be clearly marked and outlined with channelizing devices. For long-term projects, old pavement markings should be removed and new ones placed. As the work space changes, the access area may be changed, as shown in figure TA-42. Traffic control work in the exit ramp may be handled as shown in figure TA-43.

    When a work space interferes with an entrance ramp, a lane me need to be closed on the freeway. Work in the entrance ramp may require shifting ramp traffic. Traffic control for both operator is shown in figure TA-44.

6G-10. CONTROL OF TRAFFIC THROUGH INCIDENT AREAS

The primary function of traffic control at an incident area is to move traffic safely and expeditiously through or around the incident. An incident is an emergency traffic accident, natural disaster, or special event. Examples include a stalled vehicle blocking a lane, a traffic accident blocking the traveled way, a hazardous chemical spill closing a highway, floods and severe storm damage, a planned visit by a dignitary, or a major sporting event.

Emergencies and disasters may pose severe and unpredictable problems. The ability to install proper traffic control may be greatly reduced in an emergency, and any devices on hand may be used for the initial response as long as they do not themselves create unnecessary additional hazards. If the situation is prolonged, the standard procedures and devices set forth in this part of the MUTCD shall be used. Special events, on the other hand, can be properly planned for and coordinated. This part provides standards for the proper procedure for closing portions c entire roadways in conjunction with such activities.

Truck Route National Network and hazardous cargo signs are included in section 2B-43. During incidents, longer vehicles may need to follow a different route from automobiles because of bridge, weight, clearance, or geometric restrictions. Also, vehicles carrying hazardous materials may need to follow a different route from auto drivers.

The control of traffic through incident areas is an essential part of fire and enforcement operations. For these operations there must be adequate legislative authority for the implementation and enforcement of needed traffic regulations, parking controls, and speed zoning. Such statutes should provide sufficient flexibility in the application of traffic control to meet the needs of the changing conditions in incident areas.

Maintaining good public relations is necessary. The cooperation of the news media in publicizing the existence of, and reasons for, incident areas and their traffic control can be of great assistance in keeping the motoring public well informed.

Street or highway incident management signs fall into two major categories: regulatory signs and warning signs. Specifications for incident sign design are presented in section 6F-1.

The channelizing devices discussed in section 6F-5 should be used whenever possible. Flares may be used to initiate traffic control at all incidents or for short-term traffic control such as clearing incident sites, but should be replaced by more permanent devices as soon as practicable.

A short-term road closing caused by an incident such as a traffic accident may block the traveled way. Traffic may be detoured around the incident and back to the original roadway. The jurisdiction having control of the roadway will probably need to determine the detour route and install the signs. Large trucks are a primary concern in such a detour.

An incident such as a hazardous chemical spill may require closure of an entire highway. Local traffic can adjust to the closure, but through traffic must be guided around the incident and back to the original route.