Channelizing devices, barriers and arrow boards

Signs tell drivers what is coming. Channelizing devices show them, physically, where to go. A line of cones, drums or barricades draws a path through the work zone that a driver can follow without reading anything, even in rain or at night. Barriers go a step further: they do not just show the path, they physically stop a vehicle from leaving it. Arrow boards add a bright, flashing signal that a lane is closed and which way to merge. This lesson covers each of these devices, what it does and does not do, and where it belongs.

Channelizing devices

Channelizing devices guide traffic. They are designed to be seen and, when hit, to fall over or bend without causing serious damage to the vehicle or its occupants. They do not stop vehicles. That distinction matters: a line of cones beside a trench marks the edge of the work space, but it will not keep a car out of the trench.

• Cones. The most common device, easy to place and remove. Cones about 450 mm tall are used in daylight on low-speed streets; taller cones, about 700 mm or more, with retroreflective bands, are used on higher-speed roads and at night. Cones blow over in wind and from the draft of passing trucks, so they may need weighted bases or added ballast rings.
• Tubular markers. Narrow upright posts, often mounted on a weighted base or glued to the pavement. They take up less room than cones and are useful where space is tight, but they are less visible.
• Vertical panels. Flat panels with diagonal orange and white retroreflective stripes on a post or base. They are visible from far away and useful where space is narrow.
• Drums. Large barrel-shaped devices, about 900 mm tall, with alternating orange and white retroreflective bands. Drums are highly visible, look substantial to drivers and do not blow over easily, so they are the usual choice on highways and for longer-term closures.
• Barricades. Frames with one, two or three striped horizontal rails. A barricade with three rails is used to close a road or ramp completely; barricades with fewer rails mark the edge of an excavation or work area.
• Longitudinal channelizing devices. Lightweight, water-filled or interlocking plastic units that form a continuous wall. They guide traffic and pedestrians and are easy to move, but unless they are tested and accepted as barriers, they do not stop vehicles.

Spacing of channelizing devices

Devices must be close enough together that drivers see a continuous line, especially at night. Manitoba's Work Zone Traffic Control Manual and the City's standard drawings give the spacing for each speed. In the taper, where drivers are changing lanes, devices are closer together; along the work space, where drivers are going straight, they can be spaced further apart. A rough check used by many supervisors, borrowed from the US manual, is that the spacing in a taper in metres should be no more than about a fifth of the speed in km/h, and about twice that along the work space.

Barriers

Where the consequences of a vehicle entering the work space are severe, channelizing devices are not enough. Deep excavations, workers in a long-term work space beside high-speed traffic, a drop-off of more than a few centimetres at the pavement edge, and bridge decks with open edges all need positive protection: a barrier that can stop or redirect a vehicle.

• Portable concrete barriers are the most common. They are heavy precast sections connected end to end. When hit, they deflect a little and redirect the vehicle, so the work space behind them must be set back far enough from the barrier to allow for that deflection. Workers must not stand in the deflection zone behind the barrier.
• Water-filled and steel barriers that have been crash-tested and accepted for the speed can be used where concrete is too heavy or where barriers must be moved often. Many water-filled devices are channelizing devices only, so the supervisor must check the approval.
• End treatments. The blunt end of a barrier facing traffic is a severe hazard. It must be flared away from traffic, buried, or fitted with a crash cushion, or the end must be outside the clear zone.
• Truck-mounted and trailer-mounted attenuators are energy-absorbing cushions on the back of a heavy truck or trailer parked or moving upstream of the work. They protect workers in mobile and short-term work, and lesson 11 covers how they are used.

Barrier systems used on Canadian highways are generally those tested and accepted by the road authority, often using test criteria developed in the United States. The supervisor uses the road authority's list of accepted products and follows the manufacturer's installation instructions, including the required set-back for deflection.

Arrow boards

An arrow board, sometimes called a flashing arrow panel, is a large panel of lights mounted on a trailer or truck. It is the most visible signal in a work zone and is used mainly on multilane roads to tell drivers that a lane is closed and which way to merge. It has four display modes.

• Flashing or sequential arrow: a lane is closed; merge in the direction of the arrow.
• Double arrow: traffic may pass on either side.
• Sequential chevron: a lane is closed; merge in the direction shown.
• Caution mode: four corner lights or a horizontal bar, used when there is work on or near the shoulder but no lane is closed, or on two-lane two-way roads.

Two rules prevent dangerous misuse. First, an arrow pointing to the left or right is used only on multilane roads where drivers can actually merge into another lane going the same way. Second, on a two-lane, two-way road, where one lane is closed and traffic takes turns with flagpersons, an arrow board must be in caution mode only, because an arrow could send drivers into the oncoming lane. Arrow boards are placed at the start of the taper, on the shoulder or in the closed lane, and are sized for the speed: small boards for low-speed city streets, large boards for highways.

Flashing and steady-burn lights

Flashing warning lights on barricades and drums draw attention to a single hazard, such as the start of a closure. Steady-burn lights mounted in a line on channelizing devices at night help define the path drivers should follow. Flashing lights should not be used in a line along a taper, because a row of flashing lights is confusing and makes it hard to see the path.

Pedestrian devices

Where a sidewalk is closed or narrowed, pedestrian channelizing devices must be detectable to people who are blind or have low vision. That usually means a continuous bottom rail or edge close to the ground that a white cane can find, and a top rail at a height people can use for guidance, with no gaps between units. Cones and barricades with open bottoms are not detectable and should not be used alone to define a pedestrian route. Lesson 12 returns to pedestrian protection.

Choosing devices

Nadia uses a short decision program when she drafts a plan, to suggest a starting device type from the speed, the duration and whether workers will be exposed to a severe hazard.

# Suggest a starting device type for the edge of a work space (simplified, illustrative rules).
def suggest(speed_kmh, days, severe_hazard, night):
    if severe_hazard and speed_kmh >= 60:
        return "crash-tested barrier with end treatment and set-back for deflection"
    if severe_hazard:
        return "barrier or protected work space; at minimum drums with close spacing"
    if speed_kmh >= 70 or days > 3:
        return "drums or tall cones with retroreflective bands"
    if night:
        return "tall retroreflective cones with steady-burn lights"
    return "standard cones"
cases = [
    ("Larch Ave gate closure, day", 50, 1, False, False),
    ("Water service trench in street", 50, 4, True, False),
    ("Night crane erection", 50, 1, False, True),
    ("Highway driveway tie-in", 100, 6, True, False),
]
for name, s, d, sev, n in cases:
    print(f"{name:32} -> {suggest(s, d, sev, n)}")

Larch Ave gate closure, day      -> standard cones
Water service trench in street   -> barrier or protected work space; at minimum drums with close spacing
Night crane erection             -> tall retroreflective cones with steady-burn lights
Highway driveway tie-in          -> crash-tested barrier with end treatment and set-back for deflection

The water service trench on Larch Avenue was 2.4 m deep, beside an open lane at 50 km/h, for four days. The program suggested a barrier or protected work space. Red River Traffic Control Ltd. closed both lanes on that block for the deep work, which removed traffic from beside the trench completely, rather than relying on cones a metre from the edge.

Device condition

Devices wear out. Cones get crushed, their retroreflective bands peel, drums get dented and dirty, and barricade rails crack. A device that is damaged or dirty may not be visible at night and makes the zone look neglected, which encourages drivers to take it less seriously. Many road authorities use a simple rating system: acceptable, marginal (replace soon) or unacceptable (replace now). Red River Traffic Control Ltd.'s crews checked devices when loading the truck each morning and pulled damaged ones out of service, and the traffic control supervisor swapped out any that got damaged during the shift. Clean, upright, complete devices are part of the message that the work zone is real and the rules apply.

Storing devices on site

Devices not in use should be stored off the road and out of the clear zone, not stacked on the shoulder or the sidewalk, where they can be hit, blown into traffic or block pedestrians. Barriers and drums left lying beside an open lane become hazards themselves.