Passive Safety Workshop

Using the new standard

and UK Annex in practice

National Motorcycle Museum

25 June 2019

Design advice for passively safe traffic signs

to BS EN 12767 and BS EN 12899

Simon MorganMA, MSc, CEng, MICE, HonFIHE

Safety

How do traffic signs cause injury?

• Sign or part of it falls on someone.

• Sign or part of it obstructs the highway.

• Missing or damaged sign fails to give

important warning.

• Vehicle collides with sign supports.

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Over 1300 injuries per year in Britain

• Passive safety - building safer roadsides

Passive safety

• BS EN 12767:2007 and National Annex.

• BS EN 12767:2019 and National Annex.

• Highway authority should decide whether to adopt passive safety for each route and location.

• Less important for 30 mph and slower roads.

• Past accident record relevant, as for other safety measures.

• Higher cost of new structures (including lamp columns & signal poles) needs to be balanced against potential accident saving.

When to spend

on Passive Safety• Refer to IHE Sign Structures Guide 2010

www.theihe.org/news-info/ihe-publications

and Passive Safety UK guidelines:www.ukroads.org/webfiles/Guidelines%20Print%20ready.pdf

• Consider principally:– Posts/columns being replaced anyway

– Higher speed roads (40 mph and above a priority)

– Higher flow roads (or classified A or B)

– Roads with a history of single vehicle / loss of control accidents

• No need to consider:– Roads generally lined with parked vehicles

– Post/columns > 4.5 m from carriageway

– Post/columns close to bridges and solid walls

Opposing requirements

for passively safe street

furniture

The object must stand up

The object must deform safely

… for many years, even after fierce gales

and repeated loading cycles

… when hit by a vehicle

What documents

are relevant?

• Passive safety standard:

BS EN 12767:2007

(soon to become BS EN 12767:2019)

• IHE Guide

• Passive Safety Guidelines

Anything else?

Relevant standards (signs)

• Traffic signs: BS EN 12899-1:2007

• Wind actions: BS EN 1991-1-4:2005+ A1:2010

• Passive safety: BS EN 12767:2019

• Foundations:

– BS EN 1997-1:2004 + A1:2013

– BD 94/17 (will become CD 364) www.standardsforhighways.co.uk/ha/standards/dmrb/vol2/section2/bd9417.pdf

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ones you need a copy of

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UK Annex

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Crash friendly signs must comply with all

Relevant standards

(lamp columns)

• BS EN 40 (in 9 parts)

BS EN 40-3-1 and BS EN 40-3-3 most relevant

• PD 6547:2004 (guide to above two parts)

contains superseded wind speeds, so refer also to:

• UK National Annex to BS EN 1991-1-4:2005

• Passive safety: BS EN 12767:2019

Look in manufacturers’ data and relate to:

• Wind loading region (light, medium, heavy, extra heavy)

• Soil quality (poor, average, good)

• Class of any attached sign (A, B, C)

BS EN 12899-1:2007

• Multiple choice standard

• 16 performance classes

• If not specified, the manufacturer can

assume the least demanding class

• Over a billion combinations!

• UK Annex to give guidance and

consistency (updated several times since 2007 and

about to be revised again)

EN 12899

Performance classes• P 1-3 Piercing of face

• E 1-3 Edge protection of sign plates

• NR, CR Chromaticity & luminance

• B 1-2 Luminance factor class

• L 1-3, S Luminance of transilluminated signs

• U 1-3 Uniformity of luminance

• E 1-5 Illuminance of externally lit signs

• UE 1-3 Uniformity of illuminance

• PL 0-5 Point load

• DSL 0-4 Dynamic snow pressure

• TDB, TDT Temporary deflection

• PAF 1-2 Partial action factors

• SP 0-2 Surface protection

Performance classes

to specify

• WL 0-9 Wind pressure

(give class or actual pressure)

• RA 1-2 RetroreflectionRA1

‘Engineer grade’ not recommended for traffic signs

RA2 / R2

‘High intensity’: for locations other than those below

R3B

Where ‘high performance’ material is required

R3C

Material suitable for overhead gantries, etc.

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Determining wind pressure

• Generally gives much lower wind load

• OK for any situation

• Design much more complex

• Simpler design process

• Results very conservative (over-designed)

• Not suitable for certain locations

(e.g. above 250 m altitude)

Design to EN 12899 UK Annex

Design to EN 1991-1-4

Wind velocity

map

From 2010 UK

National Annex

10 further stages

to arrive at wind

load!

BS EN 1991-1-4

In practice use software

The only practical method, but:

• Does it follow the latest standards?

• Does it use the accurate local wind load?

• Does it cover the sign type required:

size, passive safety, GRP substrate, support positions?

• Does it provide for all the site circumstances:

soil type, slope, foundation type?

• Have you selected the right options and inputs?

• Do the results look reasonable?

• You are still responsible for the final design.

What steel sections are OK?

EN 12767:2019 (annex K)

89 mm dia. 3.2 mm wall CHS S355 steel OK

• Class: 100:NE:C:NR:SE:MD:0

“Results are valid also for supports made of

circular hollow steel or aluminium sections of

the same or smaller diameter and which have

a lower bending and shear capacity than

tested.”

Grades of steel

• S275 Mild steel - most widely used

• S355 High strength steel30% stronger

generally more expensive

slightly more brittle

• Tests on CHS posts were S355 grade

• We don’t really know what is the largest

S275 passively safe post …

… but Moment capacities

give us some idea:

CHS size grade capacityfactored by γm

89 × 3.2 S355 5.75 kN m

89 × 3.2 S275 4.45 kN m

89 × 4.0 S275 5.69 kN m

76 × 4.0 S355 5.01 kN m

76 × 4.0 S275 4.06 kN m

60 × 4.0 S275 2.45 kN m

All now deemed compliant in the new EN 12767

Steel Smaller Posts

• Economy

• Can be more closely spaced:

2 no. 76 mm dia. posts: 300 mm min.

3 or more 76 mm dia. posts: 750 mm min.

Previous 12767 Passive safety compliance:

Use CHS ≤ 89 mm dia. and ≤ 3.2 mm wall.

New 2019 EN 12767 Annex K:

Use any steel post with factored moment

capacity of ≤ 5.75 kN m(This includes CHS 89 × 4.0 S275)

12767 Energy classes

• HE high energy absorption

– Reduces risk of secondary accident by

stopping vehicle or slowing it significantly

• LE low energy absorption

– Post usually shears or detaches after event

• NE no energy absorption

– Vehicle not slowed

– Lower risk to occupants

ΕΝ 12767 Energy classes

Speed & safety classes

• Speed classes

– 50 km/h (31 mph) - not recommended for UK

– 70 km/h (44 mph)

– 100 km/h (62 mph)

– All classes also tested at 35 km/h (22 mph)

• Occupant safety levels: A to E

– B to E acceptable for any structure

– A only for small non-harmful supports

Other classes

• Backfill type, S, X or R

– Not an issue in UK, so NR (no requirement)

recommended

• Collapse mechanism, SE or NS

– NS perhaps preferable where there might be a risk of

secondary accidents, but no evidence in practice, so

NR recommended

• Direction of impact, MD, BD or SD

– MD (multi-directional) preferred as vehicle trajectories

in crashes are unpredictable

• Risk of Roof indentation, 0 or 1

– Class 0 (roof deformation < 102 mm) recommended

Selecting classes

for traffic sign supports

• Choice usually dictated by products available

• From new 12767 National Annex:Speed limit > 40 mph

In verges 100:NE:NR:NR:NR:MD:0

Roads with significant non-

motorised users or major risk

of items falling on other

carriageways.

100:HE:NR:NR:NR:MD:0

100:LE:NR:NR:NR:MD:0

100:NE:NR:NR:NR:MD:0

Speed limit ≤ 40 mph As above, but 70 speed

class also acceptable

100:NE:A (or 70:NE:A for ≤ 40 mph )

is OK for small non harmful structures

Selecting classes

• Only the speed class really matters (but most

products are rated OK for the fastest roads)

• So, choose the most suitable product for the

location from other considerations:

– Suitability for the location, mounting height and post

spacing

– Cost (including installation & foundations)

– Local policy and experience

– Availability

– Guarantees

Passively safe sign supports

• Steel and aluminium sections 89 mm diameter

or smaller

• Lattix and Optimast aluminium mast

• Jerol or FSP GRP supports

• Varley & Gulliver Hi Mast

• Various aluminium sections

• Cut-down lamp columns (if door needed)

Need to check chosen support is structurally

adequate as well as meeting required passive

safety classes.

Mounting height & spacingfor Passive safety

• Normal minimum mounting height: 1.8 m– Except for small non harmful structures

– Jerol and FSP tested at 1.5 m

But … “if for sighting or other reasons a sign needs to be mounted lower that this, is still vastly preferable for it to be mounted on passively safe supports than on rigid ones.”

• Clear space between supports of 1.6 m– Unless supports have been tested spaced more closely

(e.g. 76 mm CHS steel, 140mm FSP)

– 1.6 m is 1.5 m at a 20° incidence angle.

• Foundation – No more than 50mm above ground level

– Fixing bolts, etc. must not be buried.

Post spacingfor Passive safety

20°

d

= 1596 + 0.36 d

+

20 tan 20 cos

1500d

Foundations for passively safe supports

Need to resist wind and point loads

Should they also resist impact loads?For trunk roads BD94/17 clause 11.10 says they do if they have ‘flange plates’.

Most foundations are not specifically designed for this

Of over 400 vehicle impacts with their structures, SignPost Solutions found no damaged foundation (except for two that were incorrectly made and inadequate even for the wind load).

Answer: “no”: it purely an economic matter,not a safety issue.