5.1 Cones, Tubular Markers, & Vertical Panels

5.1 Cones, Tubular Markers, & Vertical Panels

In temporary traffic control (TTC) zones, channelizing devices warn and guide road users, outline the intended travel path, and physically separate traffic from work spaces, workers, equipment, and hazards. According to the Manual on Uniform Traffic Control Devices (MUTCD) Part 6, channelizing devices must present a clear, consistent, and highly visible path to drivers both day and night. Cones, tubular markers, and vertical panels form the primary tier of lightweight, portable channelization. Selecting the correct device, ensuring proper retroreflectorization, and calculating exact placement spacing are core responsibilities of certified IMSA Work Zone Technicians.

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Traffic Cones: Dimensions, Sheeting, & Specifications

Traffic cones are versatile, predominant channelizing devices used for short-duration work, lane closures, channelization tapers, and emergency traffic control. Made of commercial-grade orange PVC, rubber, or synthetic polymers, cones must withstand vehicle impacts and environmental conditions without disintegrating or causing damage to impacting vehicles.

Height Requirements by Speed and Environment

The MUTCD categorizes cone height requirements based on posted roadway speeds and time of operation:

• 18-Inch Cones (450 mm): The MUTCD minimum for daytime use and low-speed roadways; the MUTCD does not attach an mph value to "low-speed." 18-inch cones are prohibited on high-speed facilities and cannot be used for nighttime channelization under any circumstances.
• 28-Inch Cones (700 mm): Required when cones are used on freeways and other high-speed highways, at night on all highways, or whenever more conspicuous guidance is needed. 28-inch cones provide the necessary target size and vertical profile to remain visible to approaching motorists from required decision sight distances.
• 36-Inch Cones (900 mm): Frequently specified by state DOTs and local highway agencies for high-speed freeways, expressways, heavy commercial corridors, or high-wind environments. They offer enhanced stability, increased surface target area, and improved visibility over crest vertical curves.

Nighttime Retroreflectorization Standards

When cones are deployed at night, ambient streetlight illumination is insufficient. Cones must be retroreflectorized with high-intensity retroreflective sleeve sheeting. The MUTCD specifies an exact two-band configuration for 28-inch and 36-inch cones:

1. Upper White Band: A 6-inch wide white retroreflective band installed 3 to 4 inches down from the top apex of the cone.
2. Lower White Band: A 4-inch wide white retroreflective band installed 2 inches below the bottom edge of the upper 6-inch band.

This 6-inch and 4-inch sleeve combination creates a distinctive visual signature that drivers instantly recognize as a channelizing hazard boundary under vehicle headlight beams. The MUTCD specifies no sheeting type for cones; it requires only that cones be retroreflectorized or equipped with lighting devices for nighttime use, and that the retroreflective material display a similar color day or night.

Material Weighting & Ballasting Safety

Cones must remain upright and stationary despite wind gusts and high-speed vehicle air turbulence (wake effect). Ballasting must be integrated directly into the cone base through weighted rubber collars or heavy molded bases. Loose ballast, sandbags, or heavy objects placed on top of cones are strictly prohibited. Heavy items perched atop channelization devices transform into high-velocity flying projectiles upon vehicle impact, creating severe safety risks for workers and motorists.

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Tubular Markers: Design, Mounting, & Applications

Tubular markers are slender, flexible channelizing devices used where space is severely constrained or where a narrow footprint is required between adjacent travel lanes.

Physical Dimensions and Retroreflectivity

• Minimum Height: Must be at least 18 inches for low-speed daytime urban applications, but shall be a minimum of 28 inches (700 mm) when used on freeways and other high-speed highways, on all highways during nighttime, or whenever more conspicuous guidance is needed.
• Minimum Width: Must present a minimum width of 2 inches facing approaching traffic, though wider profiles (3 to 4 inches) enhance target recognition.
• Retroreflective Bands: For nighttime use, tubular markers less than 42 inches in height shall have two 3-inch wide white bands, with the top band placed a maximum of 2 inches from the top of the marker and a maximum of 6 inches between the bands. Markers 42 inches or more in height shall have four 4- to 6-inch alternating orange and white stripes, top stripe orange.

Surface Mounting and High-Density Spacing

Unlike free-standing cones, tubular markers have a small base footprint that can easily tip in traffic turbulence unless securely anchored. They are commonly fastened directly to the pavement surface using heavy-duty butyl adhesive pads, mechanical anchors, or inserted into recessed rubber bases. Tubular markers excel in the following TTC applications:

• Dividing Opposing Traffic Lanes: Separating two-way traffic on two-lane, two-way roads during temporary lane shifts or bridge rehabilitation.
• Gore Area Channelization: Delineating highway exit gore bifurcations and channelizing traffic around temporary barrier ends.
• Urban Bicycle & Pedestrian Buffers: Separating temporary multi-use paths from motor vehicle lanes in dense municipal work zones.

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Vertical Panels: Dimensions, Striping Angle, & Directionality

Vertical panels are narrow, vertical retroreflective boards designed for use in cramped work zones where lateral clearance is extremely limited, such as narrow highway shoulders, bridge decks, and concrete barrier runs.

Surface Dimensions & Mounting Heights

Vertical panels shall have retroreflective striped material that is 8 to 12 inches in width and at least 24 inches in height. The MUTCD prescribes no mounting height for vertical panels — the 24-inch figure is the minimum height of the retroreflective striped material itself.

45-Degree Downward Orange/White Striping

Vertical panels have alternating diagonal orange and white retroreflective stripes sloping downward at 45 degrees in the direction traffic is to pass. A 6-inch stripe width shall be used where the retroreflective material is 36 inches or more in height; where it is less than 36 inches, 4-inch stripes may be used. The direction of the stripe slope provides critical navigation instructions to drivers:

• Right-Sloping Panel (Panel Right): Stripes slope downward to the right. This indicates to approaching motorists that traffic must pass to the right side of the device.
• Left-Sloping Panel (Panel Left): Stripes slope downward to the left. This indicates that traffic must pass to the left side of the device.

RIGHT-SLOPING (Pass to Right)       LEFT-SLOPING (Pass to Left)
       +-----------+                       +-----------+
       | \  ORANGE |                       | ORANGE  / |
       |  \  WHITE |                       | WHITE  /  |
       |   \ ORANGE|                       |ORANGE /   |
       |    \ WHITE|                       |WHITE /    |
       +-----------+                       +-----------+
         Down to Right                       Down to Left

Technicians must verify panel orientation prior to deployment. Reversing a vertical panel confuses drivers by pointing them directly into closed work areas or oncoming traffic.

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Channelizing Device Spacing Calculations

Proper spacing of channelizing devices prevents vehicle intrusions while maintaining smooth traffic flow. Device spacing relies on the posted speed limit ((S)) prior to work zone entry.

Taper Spacing Formula ((d_{taper}))

In tapers—including merging tapers, shifting tapers, and shoulder tapers—channelizing devices should be spaced closely to form an unmistakable visual barrier. MUTCD Guidance (Section 6K.01 ¶04) is that spacing should not exceed:

[d_{taper} = S\text{ (feet)}]

where (S) is the posted speed limit in miles per hour (mph).

Example: On a highway with a posted speed limit of 55 mph, the maximum allowable distance between channelizing devices in any taper is 55 feet.

Tangent Spacing Formula ((d_{tangent}))

Along tangent sections—the longitudinal buffer space and activity area where traffic travels parallel to the work space—devices may be spaced further apart:

[d_{tangent} = 2 \times S\text{ (feet)}]

Example: On a highway with a posted speed limit of 55 mph, the maximum distance between channelizing devices along the tangent run is (2 \times 55 = \mathbf{110\text{ feet}}).

Low-Speed & Urban Curve Spacing Adjustments

On urban streets with posted speeds of 30 mph or less, or around sharp horizontal curves and intersection radii, standard spacing formulas can create gaps wide enough for drivers to mistakenly turn into closed work areas. In these environments, technicians should reduce device spacing to (\frac{S}{2}) (or 10 to 20 feet) to ensure continuous guidance and prevent driver confusion.

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Installation and Removal Protocols

Deploying and removing channelizing devices exposes workers to live traffic hazards. IMSA safety standards mandate strict sequential procedures:

1. Installation Sequence: Always install channelizing devices moving downstream with traffic flow (from the advance warning area, through the transition taper, and into the activity area). The work vehicle acts as a protective shield while workers set devices behind advanced warning signs and arrow boards.
2. Removal Sequence: Always remove channelizing devices in reverse order, moving upstream facing approaching traffic (starting at the downstream end of the termination area and working backward toward the advance warning area). Workers must keep their eyes on oncoming traffic at all times during pickup.
3. Maintenance & Inspection: Devices must be routinely inspected for physical integrity, vertical alignment, and retroreflective cleanliness. Cones or markers knocked out of position or coated with road grime must be promptly cleaned, repositioned, or replaced to maintain MUTCD compliance.