How to work out how many barriers your diversion actually needs
How many jersey barriers per metre a UAE diversion needs — turning a run length into a real order, why the 1m/2m/3m mix changes the count and per-metre cost, plus joints, tapers and spares.
The call we get on a Thursday afternoon usually starts the same way: “We’ve got the diversion approved, we start Saturday, how many barriers can you get me?” Then a pause, because nobody has actually counted. They have a length off the drawing and a gut feeling. Two days later a crane crew is standing idle because the run came up ten units short at the taper.
So here’s how to turn a diversion length into a real order: the count that arrives, sets, and closes the lane without a second truck. Get this right once and you stop guessing.
How many jersey barriers do you need per metre?
It depends entirely on the length you order, and that catches people out. A 3m unit covers three metres, so you need one barrier every 3 metres — about 0.33 barriers per metre. A 2m unit is one every 2 metres, or 0.5 per metre. A 1m unit is one per metre.
That single fact drives the whole estimate. “How many barriers per metre” has no fixed answer because it’s really “how many of which length.” Pick the length first, then the per-metre number falls out of it.
How do you turn a diversion length into an order?
Measure the centreline run, divide by unit length, then add for the taper and spares. That’s the whole method. The mistakes hide in the last two steps.
Take a straightforward job: a 300m lane closure on a Dubai arterial, protected with standard jersey barriers. The straight run alone works out like this:
- All 3m units: 300 ÷ 3 = 100 barriers
- All 2m units: 300 ÷ 2 = 150 barriers
- All 1m units: 300 ÷ 1 = 300 barriers
Same 300 metres, three very different orders. Now add the parts crews skip. At each end you need a lead-in taper to guide traffic across gradually, and the higher the approach speed the longer that taper runs — at highway speed it can eat a dozen barriers or more per end. Then a spare allowance on top for breakage, rejected units, and the short lengths you’ll want to close gaps. On that 300m job in 3m units, you’re realistically ordering closer to 115–125, not the tidy 100 the centreline suggested.
Does the length mix change your count and cost?
Yes — and not the way most people assume. The longer unit costs more each but usually works out cheaper per running metre, with far fewer joints to pin and align.
| Unit length | Barriers per metre | Joints over 300 m | Relative cost |
|---|---|---|---|
| 1 m | 1.0 | ~299 | Lowest each, highest per metre |
| 2 m | 0.5 | ~149 | Middle on both |
| 3 m | 0.33 | ~99 | Highest each, often lowest per metre |
A new precast jersey barrier in the UAE runs roughly AED 150 to AED 850 per unit, driven mostly by length, quantity, and finish. Read that against the joint column, not just the sticker price. Every joint is a place two units have to line up, get pinned, and hold alignment under a nudge from traffic — 99 of them over 300 metres is a very different install day to 299. We break the per-metre maths down further in our jersey barrier price guide.
So why order anything shorter? Curves. A rigid 3m unit chords across a tight radius and leaves a gap on the inside of the bend, where a shorter unit would follow the line. On a curved diversion you drop to 1m or 2m units through the curve so the run actually follows the alignment, then go back to 3m on the straights. The mix isn’t a cost choice there — it’s what the geometry demands.
How many joints and end treatments should you plan for?
For a continuous run, count on one fewer joint than you have barriers, plus a defined end treatment at each open end. A hundred 3m units in a line give you 99 joints; the two ends are separate. Each joint is a pin-and-hole connection that has to seat and hold alignment, and whether the run also needs anchoring depends on the site — how jersey barriers connect and when they need anchoring covers both.
The ends matter more than the joints. An exposed barrier end facing oncoming traffic is a hazard, which is why a diversion gets an angled taper rather than a blunt stop. Under BS EN 1317, the family of standards for road restraint systems, terminals and transitions are treated as their own components — the run and the end are not the same problem. On UAE roads the taper geometry comes from your approved traffic management plan, worked to the RTA Traffic Control Devices Manual and the relevant municipality’s work-zone guidance. Don’t back-solve the taper from the barriers you happen to have; size the taper from the speed limit, then order to it. The same logic sets a cone taper on a lighter closure — how to set out a lane closure with cones walks through the zones and spacing.
How many spare barriers should you order?
Add 5 to 10 percent over the calculated count, and more if the job has curves or a tight programme. That covers four things that reliably go wrong: a unit chipped or cracked in transit, a unit knocked back on delivery inspection, the short lengths you need to close a gap on a bend, and the taper barriers that never made it onto the first count.
Under-ordering is the expensive mistake, not over-ordering. A handful of spare units sitting in the compound costs you almost nothing. A run that stops 8 metres short at 2pm on install day stands a crane crew and a traffic-management team down while a replacement truck is dispatched across the emirate. We’d far rather quote you three extra barriers than send that second truck. The same count-then-add-a-spare discipline runs through the smaller car park kit too — it’s exactly how we work out how many wheel stoppers a car park needs, where the trap is counting every stall instead of only the bays that front something.
If your diversion is low-speed delineation rather than hard vehicle containment — channelling traffic through a car park or a slow works area — plastic water-filled barriers deploy faster and relocate empty, and the count works the same way by length. They don’t stop a vehicle the way a 2,400kg concrete unit does, so match the barrier to the actual threat, not just the metre count.
Frequently asked questions
How many jersey barriers do I need per metre? It depends on the length you order. A 3m unit covers three metres, so about one barrier every 3 metres — roughly 0.33 per metre. A 2m unit is 0.5 per metre; a 1m unit is one per metre. Multiply your run length by that factor, then add the taper and a spare allowance.
How do I calculate barriers for a diversion? Measure the centreline run, divide by your unit length for the straight-run count, then add barriers for the lead-in taper at each end and a 5–10% spare allowance. A 300m run in 3m units is 100 barriers before tapers and spares — realistically 115–125 ordered.
Does the barrier length mix change the price? Yes. 3m units cost more each but usually less per running metre, with fewer joints to align. 1m and 2m units cost less each but you need more of them and get more joints, so the per-metre total often ends up higher. Curves force shorter units regardless.
How many spare barriers should I order? Add roughly 5–10% over the calculated count — more with curves or a tight programme. Spares cover transit damage, rejected units, short lengths to close gaps, and the taper barriers crews forget. Under-ordering stands a crane crew down waiting on a second truck.
Do I need extra barriers for the taper? Yes. A lane closure needs an angled lead-in taper so traffic is guided across gradually, and the taper lengthens as the approach speed rises. Your traffic management plan sets it; at highway speeds that adds a dozen or more barriers at each end on top of the straight run.
The two numbers crews always get wrong are the taper and the spares. They measure the straight run, order to the metre, then stand a truck down waiting for the units the flare and the breakages ate. Order the whole geometry, not the centreline.
Get a barrier count that matches your diversion
Send us the run length, the speed limit on the approach, whether the alignment is straight or curved, the delivery emirate, and your install date. We’ll work back the unit mix, the taper, and a sensible spare allowance, and quote supply and delivery so the count that arrives is the count that closes the lane.
