Why six feet is the minimum height for a secondary sign below a post-mounted roadside sign

When you’re setting up a work-zone traffic plan, the big ideas get talked about a lot—cones, barriers, timing, and lane shifts. But there’s a small detail that matters more than you’d think: how high you mount the secondary sign under a post-mounted roadside sign. If you’ve ever wondered, yes, the minimum height is 6 feet. Let me explain why that number is more than just a rule of thumb.

Why height even matters in the first place

Imagine you’re driving through a temporary work zone. You’re scanning for clues: signs, orange cones, a worker in a bright vest. If a sign sits too low, it can get swallowed by a hedge, a parked car, or even the tilt of the sun at certain hours. That moment of visibility loss isn’t just annoying—it can create confusion, slow down reaction times, and, worst of all, cause an unsafe maneuver.

And it isn’t only about drivers. Pedestrians at the edge of a work zone, cyclists, and the crew relying on the signage all benefit when signs are easy to read. A clear line of sight means drivers can interpret the message early and react smoothly.

Here’s the thing: the height isn’t just a random choice. It’s about ensuring the sign’s message appears in the drivers’ field of view, above typical roadside clutter, and well above the bumper-to-ground distance of most vehicles. It’s a practical sweet spot that many guidelines, including those used in IPSI TTC contexts, lean on to keep information legible from a safe distance.

The 6-foot rule, in plain terms

So, what exactly does 6 feet mean here? It’s the bottom edge of the secondary sign being at least 6 feet above the ground. That distance is chosen to keep the sign out of reach of ground-based obstructions and to ensure it remains readable for the broadest audience—cars, SUVs, trucks, mowers, and the occasional delivery van that sneaks through a work zone.

You’ll notice that “minimum” is the word here. In practice, crews might adjust height based on site conditions, sight lines, or vegetation. The key is not to drop below that 6-foot threshold, because going lower increases the risk of obscurity or damage, especially in busy surface streets or highway work zones.

Think of it like eye level for visibility

Humans read best when something sits at about eye level or just a notch lower. For drivers, eye level isn’t a fixed place—speed, vehicle height, and even road curvature all shift the practical reading zone. By keeping the bottom edge of the secondary sign at 6 feet, you’re anchoring the message in a spot most drivers can catch without craning or squinting. It’s a small elevation that yields big gains in comprehension and reaction time.

How the mounting height plays with other signs

A secondary sign is typically adding information to a primary, post-mounted roadside sign. The goal isn’t to crowd the space or compete for attention; it’s to supplement the main message without creating clutter. Elevating the secondary sign helps ensure there’s a clean vertical separation between messages, so each sign preserves its own legibility.

In practice, you’ll sometimes see signs mounted above or below a main plate depending on the local layout. But when it comes to a below-the-post secondary sign, staying at or above that 6-foot mark keeps you consistent with safety and visibility standards. Consistency matters. When drivers know what to expect from a work zone setup, they react faster and more predictably.

A quick field guide you can actually use

If you’re on a job site and you want a practical checklist, here are a few pointers to make sure that secondary sign height stays right:

• Measure from the ground to the bottom edge of the secondary sign. Do it at the location where the sign will sit, not just where you think it should be.

• Use a sturdy ladder or a lift with a spotter. Safety first, always.

• Check multiple vantage points. Look from approaching traffic lanes, from a distance, and from a driver’s eye level as you’d expect them to read it.

• Consider vegetation and weather. A gusty wind or overgrown shrub can reduce visibility even at the right height.

• Keep sight lines clear. No new obstruction should compromise the line of sight to the secondary sign or the primary sign above it.

• Document and adjust if needed. If a temporary condition changes (a new fence, a parked vehicle, or a large piece of equipment), revisit the height decision.

A little digression that still stays on topic

You’ve probably noticed that some sites feel more intuitive than others. That’s often about drainage and sight line planning as much as it’s about the signs themselves. For example, if a road dips slightly or the sun is low, a 6-foot height might be ideal for readability during peak glare times. The crews who stay flexible and measure on site tend to keep visibility sharp all day, not just in the morning. It’s not glamorous, but it’s effective, and that’s what keeps work zones safe and productive.

Practical tips for IPSI TTC technicians

• Use standard hardware: Brackets, standoffs, and poles designed for this mounting height reduce wobble and vibration. If a sign shakes, it’s tough to read, and that defeats the purpose.

• Check compatibility with the primary sign: The secondary sign should be mounted in a way that avoids overlapping graphics or text from the main plate. Clear separation helps legibility.

• Think long-term: In some zones, vegetation or snow may alter how a sign is read. Plan for seasonal changes and perform periodic checks.

• Safety isn’t optional: Always secure ladders, use fall protection if needed, and keep a spotter nearby when lifting or mounting signs in high-traffic areas.

• Document site-specific decisions: If you do deviate from a standard height due to an unusual layout, record why and where. That helps future crews avoid guesswork.

Common missteps to dodge

• Mounting too low: If a secondary sign sits below 6 feet, it risks being blocked by vehicles, vegetation, or parked equipment. Drivers could miss it just when they need the information most.

• Too high, too soon: Pushing the secondary sign higher than necessary can break the expected reading pattern. It might look odd and force drivers to over-adjust their gaze.

• Neglecting maintenance: A sign that's perfectly mounted but dirty, faded, or peeling won’t deliver its message. Regular cleaning and replacement are part of good TTC practice.

• Ignoring context: Urban streets, rural roadways, and expressways each have different typical sight lines. One height fits all isn’t always the best approach; adjust while keeping the 6-foot minimum in mind.

Putting it all together

The 6-foot minimum height for mounting a secondary sign below a post-mounted roadside sign isn’t a fancy flourish. It’s a straightforward, practical choice designed to maximize readability, keep sight lines clear, and support safe, smooth traffic flow through work zones. It’s the kind of detail that doesn’t glitter in photos, but it quietly does a lot of the heavy lifting in everyday traffic control.

If you’re out on site with your team, this is one of those checks you can perform quickly and confidently: measure, confirm, and move on to the next critical task. The goal is not to win a game of sign height trivia; it’s to keep drivers informed and crews safe while the road is under repair.

A final nudge: stay curious about the space you’re working in

Work zones are living environments. The signs you place, the way you mount them, and the height you choose all interact with traffic patterns, weather, and human behavior. The more you understand those connections, the more you’ll see how a 6-foot rule quietly underpins safety in every shift.

If you ever feel unsure about a mounting height in a tricky setting, ask a teammate to take a second look and bring a measuring tool. A small pause now prevents a bigger issue later. That practical mindset—paying attention to the small details—sets apart good TTC technicians from great ones.

Quick recap for the road

• For a secondary sign mounted below a post-mounted roadside sign, aim for a minimum of 6 feet above the ground (bottom edge of the sign).

• This height supports visibility, keeps sight lines open, and aligns with safety expectations.

• On-site checks, appropriate hardware, and ongoing maintenance matter just as much as the initial installation.

• Treat every work zone as a living space: adjust for context, document decisions, and keep signs clean and legible.

If you’re thinking about the bigger picture of traffic control work, remember that clarity usually travels the farthest. When a reader can spot a sign and read it without effort, you’ve already done a lot of the hard work for them. And that, in the end, is what keeps our roads safer and work zones running smoothly.