Signs: types, sizes, placement and spacing

Signs are a driver's first contact with a work zone, and often the only information a driver gets before meeting a taper, a flagperson or a stopped queue. A good sign is the right sign, big enough, placed where drivers will see it, far enough ahead to act on, and clean, upright and working. A bad sign, or a sign that says something that is no longer true, is worse than none, because it teaches drivers to ignore signs. This lesson covers the signs used in temporary traffic control and how they are chosen, sized, placed and spaced.

Three kinds of sign

• Regulatory signs tell drivers what the law requires: speed limits, lane use, no passing, stop, do not enter, road closed. They are usually rectangular, with black on white, and disobeying them is an offence. A reduced work zone speed limit is a regulatory sign and normally needs the road authority's approval.
• Signs that warn tell drivers about conditions ahead that they might not expect: road work, a lane closed, a flagperson, a lane shift, an uneven pavement edge, trucks entering. In work zones they are normally diamond-shaped with black symbols or words on a fluorescent orange background, which sets them apart from permanent yellow warning signs.
• Guide signs help drivers find their way, for example through a detour, and in work zones they are often orange with black text.

the Transportation Association of Canada's Manual of Uniform Traffic Control Devices for Canada (MUTCDC) uses a TC (temporary condition) series for work zone signs, such as the construction ahead sign, lane closure symbol signs and the flagperson ahead sign, many of which use symbols rather than words so they can be understood in English and French and by drivers who read neither. Manitoba's Work Zone Traffic Control Manual uses the same national signs and adds policies, such as the MAXIMUM 60 WHEN PASSING WORKERS sign for provincial highways where the posted limit is 60 km/h or more. Manitoba also uses signs marking the start and end of designated construction zones, where speeding fines are doubled.

Size and visibility

Sign size grows with speed, because drivers need to read signs from further away and in less time. Work zone warning signs on urban streets are commonly 600 to 750 mm across, and on rural highways and freeways 900 mm to 1,200 mm across, with the exact sizes set out in the manual's tables for each sign and speed. Signs must be retroreflective, so they shine back in vehicle headlights at night. Fluorescent orange sheeting is the norm for temporary warning signs because it stands out in daylight, at dusk and in poor weather.

Placement

• On the right side of the road, where drivers expect signs. On multilane roads with a closure on the left, on one-way streets with two or more lanes, and on divided highways, signs are commonly placed on both sides, so drivers in every lane can see one.
• Clear of obstructions. Parked vehicles, trees, other signs, utility poles and the work itself can hide a sign. The traffic control supervisor drives the approach at the posted speed to check that each sign can be seen.
• At the right height. Portable signs on stands are mounted at least about 300 mm (1 ft) above the road surface so they can be seen over low vehicles; signs mounted on posts are higher, typically around 2 m (7 ft) to the bottom of the sign in urban areas where pedestrians and parked cars could block them, and lower in rural areas.
• Stable and crashworthy. Sign stands must be weighted with low-mounted sandbags, never with rocks, concrete blocks or other objects that become missiles when a vehicle hits them. Stands and supports should be the crashworthy types accepted by the road authority.
• Not in the pedestrian route. Signs on stands placed on a sidewalk must leave enough clear width for wheelchairs and must be detectable by people using white canes.

Spacing

Spacing between signs gives drivers time to read each sign, understand it and act before reaching the next one or the taper. Higher speeds need longer spacing because drivers cover more ground per second.

Manitoba's Work Zone Traffic Control Manual and the City's standard drawings give spacing distances by speed. On low-speed city streets, signs may be a few dozen metres apart; on a provincial highway posted at 100 km/h, spacing is measured in hundreds of metres, and the first sign may be more than a kilometre before the taper. The supervisor uses the table for the road authority that owns the road, not a rule of thumb.

A useful way to understand spacing is to think in seconds. A driver needs roughly two to three seconds to read and understand a simple sign, and more for a complex one or for a decision such as changing lanes. At a given speed, those seconds become a distance.

# How far does a driver travel while reading and acting on a sign?
def m_per_s(kmh):
    return kmh / 3.6
def feet_per_second(mph):
    return mph * 5280 / 3600
for kmh in (50, 60, 80, 100):
    d = m_per_s(kmh) * 6       # 6 s to read, decide and begin a lane change
    print(f"{kmh:>3} km/h: {d:5.0f} m covered in 6 s")
for mph in (30, 35, 45, 65):
    d = feet_per_second(mph) * 6
    print(f"{mph:>3} mph:  {d:5.0f} ft covered in 6 s")

 50 km/h:    83 m covered in 6 s
 60 km/h:   100 m covered in 6 s
 80 km/h:   133 m covered in 6 s
100 km/h:   167 m covered in 6 s
 30 mph:    264 ft covered in 6 s
 35 mph:    308 ft covered in 6 s
 45 mph:    396 ft covered in 6 s
 65 mph:    572 ft covered in 6 s

At 50 km/h, a driver covers about 83 m in six seconds; at 100 km/h, about 167 m. That is why the spacing in the manual roughly doubles or triples as speed rises, and why the advance warning area on a highway is so long.

Portable changeable message signs

Portable changeable message signs, the trailer-mounted electronic signs often seen before major work zones, are useful for warning of delays, closures, detours and dates of future work. They are not a substitute for the standard static signs required by the plan. Messages should be short, with no more than two phases (screens) and a few words per line, so drivers can read them at speed. A common failure is a long message that scrolls through several screens: drivers can read only part of it before they pass the sign.

Keeping signs honest

Signs must match what drivers will actually find. A ROAD WORK AHEAD sign left out over the weekend when no work is happening, or a lane closed sign standing beside an open lane, teaches drivers to ignore signs. The rules of thumb on the Cottonwood Place job were simple.

• Cover or remove signs as soon as the condition they describe ends, including overnight when a daytime closure is lifted.
• Use proper covers that block the whole sign face. Do not turn signs sideways or lay them flat in the ditch, where they can still be seen or blown back up.
• Inspect signs at set-up, at least once during each shift and at night, for visibility, position, damage and dirt.
• Clean signs that get splashed with mud or concrete.
• Replace damaged, faded or bent signs, which lose retroreflectivity and look neglected.

Signs for special situations

A few situations need extra signs beyond the standard sequence. Where trucks enter and leave a site across traffic, a truck entrance or trucks entering warning sign upstream of the gate tells drivers to expect slow, heavy vehicles. Where the pavement edge has a drop-off or the surface is rough, signs warning of an uneven lane or a low shoulder are used. Where a sidewalk is closed, a SIDEWALK CLOSED sign with an arrow to the alternative route is placed at the previous intersection so pedestrians can choose their route before reaching the closure, not halfway along the block. Where a bike lane is closed, a sign tells cyclists whether to merge into traffic or use another route. Where workers will be present at night or the closure stays overnight, signs must be retroreflective and the arrangement must make sense in the dark.

Common sign problems found in inspections

When Owen reviewed inspection sheets from the first two months of the Cottonwood Place job, the same few problems came up again and again: signs blown over in wind because the sandbags were too small, signs turned sideways by passing trucks, signs hidden by parked vehicles or by the bus at the stop, signs left out after the closure was lifted, and a sign on the wrong side of the street after a crew set it up in a hurry. Each problem had a simple fix: bigger sandbags and wind-rated stands, a check of every sign at mid-shift, parking restrictions on the approach block, a sign removal step in the take-down sequence and a printed copy of the plan in every truck. None of the fixes cost much, and together they made the zone noticeably clearer for drivers.

Who may place a sign

Placing and removing signs is itself one of the most exposed jobs in traffic control. On the Cottonwood Place job, only Red River Traffic Control Ltd.'s trained crew placed signs on Larch Avenue and Birch Street, working from the protected side of their truck where possible, facing traffic and wearing Class 3 apparel. Other workers who noticed a fallen or misplaced sign reported it by radio rather than walking out to fix it, which kept untrained people out of the road and made sure every change was recorded on the plan.