4.4
Engineering Measures Table
BUFFER ZONES
Photographs
Introduction
Effectiveness / Advantages and
Disadvantages / Case Studies
On the outskirts of villages / urban areas, or
where there is intermittent development beyond
the existing 30mph, it may be appropriate to
introduce a short (400-600m) section of
intermediate speed limit if immediate speed
reduction causes real difficulty or is likely to be
less effective.
Advantages:
 Brings vehicle speeds down in the lower limit due to
the approach in the buffer zone.
In reality this means introducing either a


Relevant Guidance
 DfT Circular 1/13 Setting Local Speed
Limits (paragraphs 37 - 39)
 No specific TAL leaflets
Disadvantages:
 Non-compliance can occur in the buffer zone due to
the character of the road the buffer zone is on eg.
rural single carriageway with no frontage
development on approach to a village on an A road.
Key Criteria
C20 - Buffer zones should only be
installed where the mean speeds in
the lower speed limit exceed the
limit. (eg. 30mph in a 30mph limit,
40mph in a 40mph limit).
C21 - Buffer zones should be no less
than 600m. In exceptional
circumstances lengths of between
400 – 600m can be considered
40mph speed limit between 30mph and
50mph\derestricted speed limits
50mph speed limit between 40mph and
derestricted speed limits
Introduction
Countdown markers have been used on the
approach to speed limit terminal signs to
highlight to drivers that they are approaching a
lower speed limit. Legislation does not prescribe
the use of countdown markers on the approach
to speed limit terminal signs.
Effectiveness / Advantages and
Disadvantages / Case Studies
Research carried out by Mayhew & Smith (1998)
showed that countdown markers have little or no effect
on vehicle speeds and can add to sign clutter.
COUNTDOWN MARKERS
Photographs
Relevant Guidance
 DfT Circular 1/13 Setting Local Speed
Limits (paragraph 58)
 TAL 1/04 – Village Speed Limits
 LTN 1/07 section 10.2.11
Key Criteria
C22 – Countdown markers are not to
be used.
They are not supported in DfT Circular 1/13 Setting
Local Speed Limits
28
Introduction
VEHICLE ACTIVATED SIGN ROUNDEL
A VAS Roundel displays the speed limit when
approached in excess of the speed limit.
Roundels are not repeater signs as they only
display the speed limit when it is exceeded.
VEHICLE ACTIVATED SIGNS & SPEED INDICATION DEVICES
Effectiveness / Advantages and
Photographs
Relevant Guidance
Disadvantages / Case Studies
Advantages:
 Simple, clear and easy for motorists to understand
 Suitable for a wide range of locations and
installation types.
 Some models can be set to display different speed
limits, increasing their flexibility.
 Signs are blank when not activated, limiting their
visual intrusion.
Disadvantages:
 Without explanatory wording, does not give
motorists the reason for the need to slow down.
 Only gives motorists a limited amount of information
about their speed.
 DFT Circular 1/13 Setting Local Speed
Limits, para 57
 LTN 1/07 Traffic Calming - Section 9
Vehicle activated devices
 TAL 1/03 - Vehicle Activated Signs
Key Criteria
C23 - The existing signing, lining and
location of existing signs must be
reviewed prior to a vehicle activated
roundel being considered.
C24 - A vehicle activated roundel
should not be deployed unless it is
clear that fixed signing cannot
remedy the problem.
C25 - At least 3 personal injury
collisions have been recorded that
are relevant to the location of the
vehicle activated roundel within the
last three years, with at least 1 being
attributed to speed.
C26 - When considering a vehicle
activated roundel, existing mean
vehicle speeds must exceed the
speed limit (eg. 30mph in a 30mph
limit).
C27 - Vehicle activated roundels
should generally be considered as
part of a package of measures.
HAZARD WARNING VEHICLE ACTIVATED
SIGN
This is a vehicle activated sign that warns of a
specific hazard if a vehicle is approaching at an
excessive speed, or in some cases where the
vehicle is of an excessive height or weight.
Typical hazards include sharp bends,
roundabouts or junctions.
Advantages:
 Gives motorists a reason to slow down, increasing
the likelihood of appropriate driving for the situation.
 States the nature of a hazard, making motorists
more alert to it.
 Can be tailored to the exact requirements of a site,
increasing effectiveness.
 Can have a threshold speed set at an appropriate
speed for the hazard, even if this is less than the
speed limit.
 Signs are blank when not activated, limiting their
visual intrusion.
Disadvantages:
 Need to be carefully designed so as not to present
motorists with too much information, which could be
distracting.
 Mobile or temporary installations are largely
unsuitable for locations with permanent hazards
where a road sign is preferable.
C28 - The existing signing, lining and
location of signs must be reviewed
prior to a vehicle activated sign
being considered.
C29 - A hazard warning vehicle
activated sign should not be
deployed unless it is clear that fixed
signing and / or other cost effective
treatments cannot remedy the
problem.
C30 - At least 3 personal injury
collisions have been recorded that
are relevant to the location of the
hazard warning vehicle activated
sign within the last three years, with
at least 1 being attributed to speed
and / or visibility.
C31 - Hazard warning vehicle
activated signs should generally
considered as part of a package of
measures.
29
SPEED INDICATOR DEVICE (permanent)
Speed Indicator Devices are vehicle activated
signs that measure and display the speed of an
approaching vehicle. Rather than simply
displaying the speed limit or a hazard warning
when the speed limit is exceeded. The speed of
each vehicle is displayed whether the vehicle is
exceeding the speed limit or not. Some SIDs
use number plate recognition technology to
identify the vehicle activating the device.
SPEED INDICATOR DEVICE (mobile)
The same as permanent Speed Indicator
Devices except that these can be moved to
different locations as and when required.
Following the successful trial of three mobile
SIDs during 2009, Hertfordshire Constabulary
have now equipped each of its Safer
Neighbourhood Teams with a SID sign They are
also available to Community Speed Watch
groups to jointly assist in tackling the problem
of inappropriate speed within our communities.
EFFECTIVENESS OF VEHICLE ACTIVATED
SIGNS SUMMARY
Advantages:
 Can be more informative than a speed limit roundel.
 Can be applied to almost any speed limit.
 Have the ability to record traffic speeds to ascertain
whether a speeding issue is actual or perceived.
Disadvantages:
 Cannot be used for speed enforcement purposes
as they currently do not have Home Office
approval.
 Does not by itself inform motorists if they are
complying with the law.
 Does not relate to a hazard.
 Displays information that is already available to the
motorist via their speedometer.
Advantages:
 Can be more informative than a speed limit roundel
 Can be applied to almost any speed limit.
 Can be moved to locations as and when required.
 Can have more of the desired effect than a
permanent sign due to motorists not expecting to
see the sign.
 Have the ability to record traffic speeds to ascertain
whether a speeding issue is actual or perceived.
Disadvantages:
 Cannot be used for speed enforcement purposes
as currently do not have home office approval.
 Do not by themselves inform motorists if they are
complying with the law.
 Do not relate to a hazard.
 Display information that is already available to the
motorist via the speedometer.
C32 - The signing and lining and
location of existing signs must be
reviewed prior to a speed indicator
device being considered.
C33 - A speed indicator device
should not be deployed unless it is
clear that fixed signing cannot
remedy the problem.
C34 - At least 3 personal injury
collisions have been recorded that
are relevant to the location of the
speed indicator device within the last
three years, with at least 1 being
attributed to speed.
C35 - When considering a speed
indicator device, existing mean
vehicle speeds must exceed the
speed limit (eg. 30mph in a 30mph
limit & 40mph in a 40mph limit).
C36 – Speed Indicator Devices will
show vehicle speeds when
exceeding the speed limit by 20%.
Beyond this tolerance the ‘sad face’
symbol will be used. This is to
discourage drivers trying to record
high speeds on the speed indicator
device.
C37 - Speed indicator device should
generally considered as part of a
package of measures.
Effectiveness:
LTN 1/07 notes:


Speed limit repeater signs reduced mean speeds of
traffic by an average of between 3 and 9 mph The
higher reductions being where the speed limit had
also been reduced by 10mph.
Vehicle activated junction and bend signs reduced
mean speed by upto 7mph. Speeds exceeding the
limit were also reduced. Reductions tended to be
greater at the speed limit repater signs.
30
Introduction
Home Zones aim to improve the quality of life in
residential roads by making them places for
people, instead of just being thoroughfares for
vehicles. The key elements to a Home Zone
are:
 Community involvement to encourage a
change in user behaviour
 For the road to be designed in such a way
as to allow it to be used for a range of
activities and to encourage very slow
vehicle speeds (usually involving sensitively
designed traffic calming).
Effectiveness / Advantages and
Disadvantages / Case Studies
A study was carried out in 2007 to assess the
effectiveness of Home Zones in Scotland – the
evaluation of which can be applied across all Home
Zone schemes implemented in the United Kingdom.
Advantages:
 Community involvement and empowerment.
Disadvantages:
 Only minor changes in vehicle speeds or volumes
were achieved.
 Funding is a key issue, largely due to the significant
sums involved in implementing Home Zone projects
and the difficulty in synchronizing development with
council and external funding sources.
 From the Home Zones included within the Scotland
evaluation exercise, there is only limited evidence
that the schemes have resulted in increased
community use of outdoor space.
HOME ZONES
Diagram
Relevant Guidance
 Transport Act 2000
 SI 2006 No. 2082 - The Quiet Lanes and
Homes Zones (England) Regulations
2006
 DFT Circular 2/06 The Quiet Lanes And
Home Zones (England) Regulations
2006
 LTN 1/07 Traffic Calming - Section 3.1
Shared road space
 TAL 8/02 Home Zones - Public
Participation
 TAL 10/01 Home Zones - Planning and
Design
 Manual for Streets
Key Criteria
C38 - Home Zones will only be
considered where mean speeds are
under 24mph.
C39 - A Home Zone will only be
considered where the afternoon peak
flows are less than 100 vehicles.
C40 - Due to their expense, all
requests for Home Zones will be
considered by the Speed
Management Group.
31
Introduction
Quiet Lanes are minor rural roads that are
appropriate for use by walkers, cyclists, horse
riders and motorised users. These roads should
have low levels of traffic, travelling at low
speeds.
The aim of Quiet Lanes is to maintain the
character of minor rural roads by seeking to
contain rising traffic growth that is widespread in
rural areas.
The Quiet Lanes concept involves three key
elements:
 Local community engagement to encourage
a change in driver behaviour;
 Area wide direction signing strategy to reroute traffic; and
 Quiet Lane network signing.
The concept is aimed at identifying networks of
minor rural roads and is not solely about
addressing issues on individual roads. Where
possible public rights of way should be included
within these networks.
Effectiveness / Advantages and
Disadvantages / Case Studies
QUIET LANES
Photograph & Diagram
Advantages:
 Does not require any significant physical traffic
calming measures
 Is particularly appropriate for rural areas
Disadvantages:
 Effectiveness based on pilot schemes is
questionable
Relevant Guidance
Key Criteria
 SI 2006 No. 2082 - The Quiet Lanes and
Homes Zones (England) Regulations
2006
 DFT Circular 2/06 The Quiet Lanes And
Home Zones(England) Regulations 2006
 LTN 1/07 Traffic Calming - Section 3.1
Shared road space.
 TAL 3/04 - Quiet Lanes
C41 - Based on evidence collated
from previous work, Quiet Lanes will
not be further implemented due to
their limited success.
Relevant Guidance
Key Criteria
National Pilot Projects:
Quiet Lanes pilots first took place in Kent and North
Norfolk. Before and after surveys were carried out
which showed mixed results in terms of vehicle speeds
with changes of between +0.1mph and – 2.3mph.
The monitoring also showed that vehicle flows were
reduced slightly compared to control roads in both of
the demonstration projects.
Hertfordshire Pilot Project
Hertfordshire then followed with its own pilot in the
country lanes between Ayot Green and
Wheathampstead. The before and after study showed
that there were no significant reductions in vehicle
speeds.
The concept is not intended as a device to
traffic calm busy roads or to address issues of
rat running and heavy goods vehicle
movements.
GATEWAY AND ENTRY FEATURES
Effectiveness / Advantages and
Photographs
Disadvantages / Case Studies
Introduction
Gateways are used to signify the approach into
a settlement, or a traffic calmed area. They can
take many different forms, but those
implemented to date have most commonly
incorporated:
 a distinctive change in road surface colour
or material
 a prominent sign to alert drivers to the
calmed area
 ‘Dragons Teeth’
Gateway Features are normally used on the
approach to settlements to reinforce a lower
speed limit and reinforce the village identity.
Advantages:
 Highlights a change in speed limit.
 A village gateway reinforces the village identity.
Disadvantages:
 Reductions in speeds can be difficult to quantify as
gateways and entry features are often combined
within a package of measures.
Gateway Feature:
 LTN 1/07 Traffic Calming - Section 7
Gateways and entry treatments.
 TAL 1/94 VISP – a summary (VISP =
Village Speed Control Work Group)
 TAL 13/93 Gateways
 TAL 2/94 Entry Treatments
C42 - Gateway and entry features will
only be considered as part of a
package of measures to assist in the
reduction of vehicle speeds.
C43 - Careful consideration will be
given to material choices for
gateway and entrance features with
respect to future maintenance.
Effectiveness:
TAL 1/94 states that:

Minor gateway treatments achieved reductions in
85th percentile speeds which were generally below
3mph at the gateways and below 2mph.
32
An entry treatment is a form of a gateway and is
usually used in urban areas. Entry treatments
have been developed for use at side roads to let
drivers know that they are leaving a major road
and entering an area of different character,
which may be a residential road. They may
indicate the start of a series of traffic calming
measures, or they may identify the gateway at
the boundary of a 20mph zone or Home Zone.
Introduction
Chicane designs vary considerably but most fall
into two broad categories:
 Single lane working, consisting of staggered
build outs, narrowing the road so that the
traffic from one direction has to give way to
opposing traffic.
 Two way working, using build outs to provide
deflection, but with lanes separated by road
markings or a central island.
A single lane working chicane allows traffic flow
in both directions, but there is only room for
one vehicle to pass at a time. Generally priority
is given to one direction, so that the possibility
of vehicle conflicts is minimised. Priority should
be given to vehicles leaving a traffic-calmed
area, so that the speed of vehicles entering is
reduced.

With more significant treatments at gateways,
speed reductions of 6 - 7mph were attained, with
reductions in villages of 2-3 mph.

Major gateways relying on more physically
restrictive treatments were installed. Reductions in
85th percentile speeds were 10mph in some cases,
though within villages these schemes did not show
any greater speed reductions that the other
gateway schemes.
Effectiveness / Advantages and
Disadvantages / Case Studies
Advantages:
 Can effectively reduce vehicle speeds.
 Can reduce overtaking manoeuvres.
Entry Treatment:
CHICANES
Photographs
Single Lane Working Chicane:
Disadvantages:.
 Cannot be used on heavily trafficked roads.
 Only effective on roads where the flows in both
directions are balanced.
Relevant Guidance
 LTN 1/07 Traffic Calming - Section 6.4
Chicanes.
 TAL 12/97 Chicane Schemes
 TAL 9/94 Horizontal Deflections
Key Criteria
C44 - When using single way
working, two way vehicle flows
should not exceed 3, 000 vehicles
per day and will not exceed 4, 000.
C45 – Chicanes can be used on
roads with a speed limit of 40mph or
below.
Two Way Working Chicane:
Two way working chicanes require more
carriageway width than single lane chicanes,
as they allow two vehicles to pass in opposite
directions at the same time. Where chicanes
do not have a central divider, vehicles can
encroach into the opposing traffic lane, and this
may result in less speed reduction being
achieved, and / or safety being compromised.
33
Introduction
A pinch point is where the road is narrowed
from both sides at the same position along the
road for a distance of 5 to 10m. By
implementing this measure, the carriageway
width can be restricted so that only one vehicle
at a time may pass, or so that two vehicles can
pass slowly. Roads with a high frequency of
buses and / or heavy goods vehicles need a
wider carriageway width between the pinch
points.
Introduction
Central islands and refuges can be installed in
the middle of the carriageway to narrow the
width of the traffic lanes and assist in reducing
vehicle speeds. Such facilities must be
accompanied by the relevant road markings.
Effectiveness / Advantages and
Disadvantages / Case Studies
PINCH POINTS
Photographs
Advantages:
 Can effectively reduce vehicle speeds.
 Can reduce over taking manoeuvres.
 Can also provide crossing points for pedestrians.
Relevant Guidance
 LTN 1/07 Traffic Calming - Section 6.3
Narrowings.
Advantages:
 Can effectively reduce vehicle speeds.
 Can reduce over taking manoeuvres.
 Can also provide crossing points for pedestrians.
C46 - Pinch points will not be used in
isolation to reduce vehicle speeds –
only as part of a package of
measures.
C47 - Pinch points will not be used in
a road with a speed limit above
40mph.
Disadvantages:.
 Cannot be used on heavily trafficked roads.
CENTRAL ISLANDS AND REFUGES
Effectiveness / Advantages and
Photographs
Disadvantages / Case Studies
Key Criteria
Relevant Guidance
Key Criteria
 LTN 1/07 Traffic Calming - Section 6.6.3
 TAL 7/95 Traffic islands for speed
control
C48 – Central islands and refuges
will only be used as part of a
package of measures in order to
reduce speeds. They will not be used
in isolation.
Disadvantages:
 Can reduce the road space available for cyclists.
34
Introduction
Round top and flat top humps have been used
extensively across Hertfordshire.
Flat top humps having the added benefit that
they can also be used as raised crossing points
in appropriate locations.
Introduction
Cushions are favoured more commonly over
road top and flat top humps.
ROUND TOP AND FLAT TOP HUMPS
Effectiveness / Advantages and
Photographs
Disadvantages / Case Studies
 SI 1999 No. 1025 - The Highways (Road
Humps) Regulations 1999
 DFT Circular 4/96 Road humps
 LTN 1/07 Traffic Calming - Section 4
Road humps
 TAL 10/00 Road humps: discomfort,
noise, and ground-borne vibration
 TAL 9/98 Sinusoidal, "H" & "S" road
humps
 TAL 8/96 Road humps and groundborne vibrations
 TAL 7/96 Highways (Road Humps)
Regulations 1996
 TAL 2/96 75mm High Road Humps
 TAL 7/94 "THUMPS" Thermoplastic road
humps
 TAL 3/91 Speed control humps Scotland, England and Wales
 Bus Infrastructure in Hertfordshire – A
Design Guide Guide (June 2011)
 Hertfordshire Hump Construction
Protocol
Advantages:
 Can effectively reduce vehicle speeds.
 Can also provide crossing points for pedestrians.
Disadvantages:
 Can cause additional noise when vehicles traverse
the features.
 Can be difficult to construct the feature at the correct
gradient.
 Can cause discomfort for bus passengers.
 Can cause adverse effects for bus operation.
 Can be uncomfortable for cyclists to traverse.
Effectiveness / Advantages and
Disadvantages / Case Studies
Advantages:
 Can effectively reduce vehicle speeds.
 Buses can traverse cushions allowing a smooth
transition for passengers.
 Bolt down cushions are manufactured and can be
installed to exacting specifications.
 Allows cyclists to by-pass.
 Quieter than road top humps.
Disadvantages:
 Can allow HGVs to traverse the cushions without
the need to reduce speeds due to wider wheel
base.
Relevant Guidance
CUSHIONS
Photographs
Relevant Guidance
As for round tops & flat tops above, and;
 TAL 1/98 Speed cushion schemes
 TAL 4/94 Speed cushions
Key Criteria
C49 – ‘Bus Infrastructure in
Hertfordshire – A Design Guide’
recommends that these should not
be less than 25m from a bus stop,
also that speed cushions are
preferred to tables.
C50 - Round top humps are not
permitted on bus routes and the
primary route network.
Key Criteria
C51 – The ‘Bus Infrastructure in
Hertfordshire – A Design Guide’
recommends that measures need to
be taken to ensure there is no
parking adjacent to the cushions and
that the enforcement authority is
consulted.
C52 – Bolt down cushions will be
used.
35
Introduction
Rumble devices are designed to provide a
vibratory and/or audible effect. They are
intended to alert drivers to take greater care in
advance of a hazard such as a bend or junction,
and to help in reducing vehicle speeds.
Reliance should not be placed on such traffic
calming surfaces alone when seeking speed
reduction.
Effectiveness / Advantages and
Disadvantages / Case Studies
RUMBLE STRIPS
Photographs
Advantages:
 Relatively inexpensive to install.
Relevant Guidance
 LTN 1/07 Traffic Calming - Section 5
Rumble devices and overrun areas
 TAL 11/93 Rumble devices.
Disadvantages:
 Research indicates minimal speed reduction of
around 1mph.
 Not the most appropriate traffic calming for urban
areas due to noise.
Key Criteria
C53 – Rumble strips should be used
across the full width of the
carriageway to avoid overtaking.
C54 – Rumble strips can only be
used at least 200m from any
residential property.
C55 – Rumble strips should only be
considered as part of a package of
measures.
Effectiveness:
Extract from LTN 1/07:
“A study of available information (Webster & Layfield,
1993), found that the overall effect of rumble strips and
areas on 85th percentile vehicle speeds was a reduction
of 3 mph (about 6 per cent). There was evidence from
some sites that ‘after’ speeds increased slightly with
time but were still below the ‘before’ installation speeds.
Further rumble area and ribline sites have been
reported (Barker, 1997) with speed reductions of up to 6
mph, but again there was evidence from one site that
the ‘after’ speeds increased over time.”
Introduction
TRL Ltd was commissioned to develop
a profile that would create noise and vibration
within vehicles passing over it, but not increase
noise levels significantly for those outside the
vehicles.
RUMBLEWAVE SURFACING
Effectiveness / Advantages and
Photographs
Disadvantages / Case Studies
Advantages:
 A quieter alternative to rumble strips.
 Considered suitable for residential areas.
Relevant Guidance
 LTN 1/07 Traffic Calming - Section 5
Rumble devices and overrun areas
 TAL 1/05 Rumblewave Surfacing
Key Criteria
C56 – Rumblewave surfacing should
only be considered as part of a
package of measures.
Disadvantages:
 Minimal speed reduction (1 mph).
 Expensive to install compared to rumble strips
 Effectiveness is questionable.
Effectiveness:
According to TAL 1/05 the sites monitored showed
overall decreases in mean speed of between 0.2 and
1.9 mph. The 85th percentile measurements showed a
similar reduction.
Extract from LTN 1/07:
“Changes in vehicle speed as a result of rumblewave
surfacing are reported in TRL Report 545 (Watts et al.,
2002). The average speed reductions were just over 1
mph.”
36
Introduction
Mini roundabouts assist in giving easier access
from side roads. A mini roundabout should not
be considered as a traffic calming measure in
isolation, and should only be considered as a
package of measures.
Effectiveness / Advantages and
Disadvantages / Case Studies
MINI ROUNDABOUTS
Photographs
Relevant Guidance
 DMRB VolSec 6 Road Geometry
TD54/07
Bus Infrastructure in Hertfordshire – A
Design Guide (June 2011)
Key Criteria
C57 – The ‘Bus Infrastructure in
Hertfordshire – A Design Guide’
recommends that the central dome
of a mini roundabout is to be no
more than 75mm high, with side
slopes of less than 1:20.
C58 – Mini roundabouts should only
be considered as part of a package
of measures to reduce vehicle
speeds.
37