The Contractor, Utility Company, or Public Agency performing the work shall furnish and install all necessary traffic control devices prior to the start of construction or maintenance operations. This same organization shall continuously patrol the work zone throughout the duration of construction to ensure that all traffic control devices are in place, are clean, visible, and are operating properly.
TTC devices, which are not required at any time, shall be removed, covered, or otherwise shielded from traffic. All TTC devices shall be removed or relocated as the work is finished or as work conditions change.
TTC devices include: signs, channelizing devices (barricades, traffic cones, drums, etc.), temporary pavement markings, warning lights, and arrow panels. The use of each of these devices is described below.
A. SIGNS
There are three categories of TTC signs: regulatory signs, warning signs and guide signs. Regulatory signs, such as "Keep Right" and "Road Closed" signs, are to be black on white. Warning signs for TTC zones and temporary guide signs such as detour route signs shall be black on orange.
All signs used at night shall be either retro-reflective in accordance with Section 633 of the Standard Specification for construction of Roads and Bridges on Federal Highway Projects (FP-74) or illuminated to show similar shape and color both day and night.
Standard orange flags and/or flashing warning lights (see Section 18-D) may be used in conjunction with signs to form high-level warning devices (see Figure 7).The flags and or flashers must not block the sign legend.
Advance warning signs should be placed in the shoulder on the right side of the traffic flow and shall face, and be visible to, the approaching traffic. On one-way and median- divided streets, supplemental advance warning signs should also be placed in the shoulder on the left side of the road. Such supplemental signs are required when closing the left lane of a one-way or median divided Street. Advance warning signs should not be placed in the travel lane.
Ground-mounted signs installed at the side of the road in rural areas shall be mounted at a height of at least 5 ft, measured from the bottom of the sign to the near edge of the pavement. In business, commercial, and residential districts where parking and/or bicycle or pedestrian movement is likely to occur, or where there are other obstructions to view, the distance between the bottom of the sign and the top of the near edge of the traveled way shall be at least 7 ft.
Signs mounted on barricades and barricade / sign combinations shall be crashworthy. Where it has been determined that the accommodation of pedestrians with disabilities is necessary, signs shall be mounted and placed in accordance with Section 4.4 of the "Americans with Disabilities Act Accessibility Guidelines for Buildings and Facilities (ADAAG)" (see Section 1A.11).
Guidance: Neither portable nor permanent sign supports should obstruct pedestrian or bicycle traffic. Signs mounted lower than 7 ft. should not project more than 4 inches into pedestrian facilities.
Advance warning signs on long-term stationary projects shall be mounted on posts. On shorter-term projects, advance-warning signs may be mounted on portable supports. Figure 8 shows the height and lateral clearance requirements for both of these types of mountings. Where appropriate, signs may be mounted on or above barricades. For mobile operations, a large sign may be mounted on a maintenance vehicle stationed in advance of the work area or moving along with it.
Signs, which are typically used in TTC zones, are shown in Diagrams 1 through 29. The sizes shown are standard for most urban conditions. Larger signs are recommended for highways. Smaller signs may be used on low volume local streets.
The Contractor, Utility Company, or Public Agency performing the work shall furnish, install, and maintain all temporary signs. Only CDOT forces shall install, remove, or relocate any permanent signs within the Right-of-Way. CDOT forces will usually correct any conflicts within 24 hours of being notified. Notification of conflicting signs may be made directly to the Transportation Operations Division or by calling the general information number for CDOT.
B. PORTABLE CHANGEABLE MESSAGE SIGNS
Portable Changeable Message signs shall be TTC devices with the flexibility to display a variety of messages. Each message shall consist of either one or two phases. A phase shall consist of up to three lines of eight characters per line. Each character module shall use at least a five wide and seven high pixel matrix. They should not obstruct pedestrian or bicycle traffic and must not violate the noise ordinance at night time.
The primary purpose of Portable Changeable Message signs in TTC zones is to advise the road user of unexpected situations. Some typical applications include the following:
Messages should be designed taking into account the following factors:
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Each phase should convey a single thought.
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If the message can be displayed in one phase, the top line should present the problem, the center line should present the location or distance ahead, and the bottom line should present the recommended driver action.
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The message should be as brief as possible.
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When abbreviations are used, they should be easily understood.
Portable Changeable Message signs shall be equipped with a power source and a battery back-up to provide continuous operation when failure of the primary power source occurs.
The bottom of the message sign panel shall be a minimum of 7 ft. above the roadway. Portable Changeable Message signs should be used as a supplement to and not as a substitute for conventional signs and pavement markings.
Portable Changeable Message signs should be placed on the shoulder of the roadway or, if practical, further from the traveled lane. They should be delineated with retro-reflective TTC devices.
When Portable Changeable Message signs are not being used, they should be removed or shielded, if removal is not practical. If the previous two options are not feasible, they should be delineated with retro-reflective TTC devices.
C. CHANNELIZING DEVICES
The purpose of channelizing devices is to guide drivers and pedestrians through a TTC zone and to protect the workers inside the work area. Channelizing devices include drums, cones/tubular markers, and barricades. These devices have similar functions and can be interchanged for most applications. The best device to use will be dependent on the duration of the work, the type of work, the time of day and level of safety desired.
Channelizing devices are elements of a TTC system and should not be used without appropriate warning signs and/or other devices. To effectively guide traffic, channelizing devices must be placed in series to form tapers or to separate traffic from hazards. The spacing of the devices, to provide good guidance, is dependent on the speed of the approaching traffic. To provide good guidance, the type of channelizing device used should be consistent throughout a TTC zone. Types of devices in a series should not be mixed. A single channelizing device shall not be placed alone in a travel lane.
The standard design and typical application of each type of channelizing device is described below.
C1. DRUMS
Drums used for traffic warning or channelization shall be constructed of lightweight, flexible, and deformable materials and shall have a minimum height of 36 inches. The outside base diameter shall be at least 21 inches and no greater than 24 inches. The outside upper diameter shall be at least 18 inches but shall not exceed the outside base diameter. Drums should weigh between 12 and 15 pounds. The base shall be designed to accommodate a sandbag of 40 pounds to 60 pounds in weight as ballast. Ballast shall not be placed on top of the drum because it could become a hazard when struck. Drums shall have closed tops to prevent water and debris from accumulating in the bottom of the drums.
The markings on drums shall be alternating orange and white horizontal, circumferential, retro-reflective stripes 6 to 8 inches wide. There shall be at least two orange and two white stripes on each drum. Any non-retro-reflective spaces between the horizontal orange and white stripes shall not exceed 2 inches wide (see Figure 9).
Drums are most commonly used to delineate the flow of traffic but may also be used to mark specific hazards.
Drums have the appearance of being formidable obstacles and, therefore, command the respect of drivers. They are portable enough to be shifted from place to place within a TTC zone to accommodate changing conditions but are generally used in situations where they will remain in place for a prolonged period. Drums are the recommended channelizing device for long-term and intermediate-term stationary projects.
C2. CONES AND TUBULAR MARKERS
All cones and tubular markers shall be predominantly orange and made of a material that can be struck without damaging vehicles on impact. Cones and tubular markers shall be at least 18 inches high when used on low speed, low volume roads. A minimum height of 28 inches is required on thoroughfares and other highways. Tubular markers shall be at least 2 inches wide. Cones and tubular markers used at night shall have retro-reflectorized bands as shown in Fig. 9.
Like drums, traffic cones are most commonly used to delineate the flow of traffic but may also be used to mark specific hazards. Cones are lightweight and very portable and are typically used on projects with very short durations where the site is not left unattended. Care must be taken when placing cones to ensure that they will not be blown over or displaced by wind or moving traffic. If a site is to be left unattended, cones should be double stacked to increase their weight and stability.
Tubular markers have less visibility than other channelizing devices but may be useful where space limitations do not allow for the use of larger, more visible devices. A typical application of tubular markers is to separate opposing flows of traffic. If a site is to be left unattended the tubular markers should be affixed to the pavement with adhesive.
C3. BARRICADES
A barricade is a portable device having one to three horizontal rails with alternating orange and white retro-reflective stripes. The stripes slope downward at an angle of 45 degrees in the direction traffic is to pass the barricade (see Figure 9).
Barricade rails should be supported in a manner that allows them to be clearly seen by motorists and provide stable support. Because barricades are often located adjacent to traffic and are subject to impact from errant vehicles they should be constructed of lightweight materials and should not have rigid bracing. Barricades may be ballasted with sandbags on the lower parts of the frame to prevent being blown over by wind or traffic. As with drums, solid objects such as rocks or chunks of concrete should not be used as ballast.
There are three types of barricades: Type I, Type II, and Type III. The type of barricade is determined by the number of horizontal rails with reflective striping (Type I barricades often include a second unstriped rail which is necessary for stability).
Type I and Type II barricades are intended for use in situations where traffic is maintained through the TTC zone. As with drums or cones, Type l or Type II barricades may be used to delineate the flow of traffic but may also be used to mark specific hazards. A single drum or barricade shall not be placed in an open travel lane.
Like drums, barricades have the appearance of being formidable obstacles and, therefore, command the respect of drivers. They should be portable enough to be shifted from place to place within a TTC zone to accommodate changing conditions but are generally used in situations where they will remain in place for a prolonged period. Type I barricades are adequate for all such applications in the city. Type II barricades are recommended for highways.
Type III barricades are used for the closure of all or a portion of the roadway. When used to close the entire roadway to all traffic, a sufficient number of Type III barricades shall be used to completely close the roadway.
When access by construction vehicles is required, the contractor, utility company, or agency doing the work is responsible for properly replacing the barricades at the end of the workday.
When access to local dwellings and businesses is to be maintained beyond the point of the closure, then an adequate opening shall be provided between the barricades to allow safe ingress and egress through the closure. A single Type III barricade may be used at the beginning of the activity area to help delineate the closed portion of a roadway.
D. TEMPORARY PAVEMENT MARKINGS
Properly maintained pavement markings can provide the best delineation around long-term stationary work zones. Pavement markings are not susceptible to being blown down or moved by wind or traffic and are not easily changed by vandals. This "permanence" makes temporary pavement markings ideal for long-term stationary projects but also makes them inappropriate for shorter duration projects.
On long-term stationary projects, the contractor, utility company, or agency doing the work shall remove any existing pavement markings which conflict with the temporary traffic flow. New temporary markings, which direct traffic through the TTC zone, shall be installed and maintained for the duration of the project. Appropriate permanent markings shall be re-installed upon completion o the project.
Existing conflicting markings shall be obliterated so as to be unidentifiable as pavement markings under day or night, wet or dry conditions. All temporary pavement markings shall meet the specifications for size, placement, and color of Part 3 (pavement markings) of the Manual on Uniform Traffic Control Devices and the current CDOT standards. Temporary pavement markings may either be painted or may be formed using temporary tape. Paint is recommended for any application, which is intended to remain longer than 2 weeks. All temporary markings shall be retro-reflective. The temporary markings should be checked each day and each night to ensure good visibility. Proper maintenance is critical for temporary markings to be effective.
E. WARNING LIGHTS
At night, when drivers' visibility is sharply reduced, it is often desirable and necessary to supplement retro-reflectorized signs and channelizing devices with warning lights. There are three types of warning lights:
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TYPE A low-intensity flashing warning lights are most commonly mounted on barricades, drums or advance warning signs and are intended to continually warn drivers that they are approaching or are adjacent to a hazardous area.
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TYPE B high-intensity flashing warning lights are normally mounted on advance warning signs or on independent supports. Since these lights are effective in daylight and in darkness, they are designed to operate 24 hours per day.
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TYPE C steady- burn lights are usually mounted on drums and barricades and are intended to be used to delineate the edge of the travel path, lane closures or similar situations.
TYPE A and TYPE B flashers shall not be used in a longitudinal display to delineate a travel path in an attempt to "guide" traffic, but only as a device to alert motorists. Where lights are needed to delineate the travel path through or around obstructions in a construction or maintenance area, the delineation shall be accomplished by use of TYPE C steady-burn lights.
As used herein, warning lights are portable, lens directed, enclosed lights. The color of the light emitted shall be yellow. They may be used in either a steady burn or flashing mode as noted above. Warning lights shall be in accordance with the requirements of ITE Standard for Flashing and Steady Burn Barricade Warning lights (See Table 1).
F. ARROW PANELS
An arrow panel is a sign with a matrix of elements capable of either flashing or sequential displays. It is intended to provide additional warning and provide positive guidance to assist in merging and controlling traffic through a TTC zone. Arrow panels should be used in combination with, not in lieu of, appropriate barricades, signs, and other traffic control devices. Advance warning arrow panels shall meet the specifications of Table 2.
Arrow panels should have the capability of the following mode selections (see figure 10): (1) left or right flashing or sequential arrows; or (2) left or right sequential chevrons; and (3) flashing double arrow; and (4) caution.
The caution mode consists of four or more lamps arranged in a square pattern. Care must be taken to avoid driver confusion in the placement of arrow panels in the vicinity of ramps, median crossovers, and side road intersections.
Arrow panels are intended to assist with merging traffic. Arrow panels should not be used for work activities on the shoulder of the roadway except in the "CAUTION" mode because the panels can cause unnecessary lane changing. An arrow panel shall not be used on a two-lane, two-way roadway for temporary one-lane operation. An arrow panel shall not be used on a multi-lane roadway to laterally shift all lanes of traffic.
(See Figures 7 - High Level Warning Devises, Figure 8 - Height and Lateral Location of Signs Portable Mounting, Figure 9 - Channelizing Devices, Table 1 - Warning Lights, Table 2 - Arrow Panels, and Figure 10 - Arrow Panel Displays.)
