4.4
Traffic Calming Measures Table
Introduction
20mph speed limit:
 Uses signs and line marking only.
 Does not use physical engineering
measures.
 Speeding is not a problem in this area.
85th percentile speeds are 25mph or
less prior to a limit being introduced on
a Hertfordshire road.
 A 20mph speed limit is self enforcing.
 A 20mph speed limit requires repeater
signs to reinforce within the limit to
reinforce it.
 Relatively low cost to implement.
20mph zone:
 Uses physical engineering to bring
speeds down.
 A 20mph zone is self enforcing.
 A 20mph zone does not require
repeater signs. Signage is only required
at the entrance points, therefore
reducing clutter.
 Expensive to implement.
 Good at reducing vehicle speeds as
physical measures need to be
introduced.
Effectiveness / Advantages and
Disadvantages / Case Studies
20MPH LIMITS AND ZONES
Photographs
Relevant Guidance
Effectiveness:

DfT Know Your Speed Limits (2004):
The effect of a 20mph limit or zone will depend upon the
circumstances at each particular location or area. The
Department Transport released a document entitled
Speed: Know your limits in 2004. It summarises the
effectiveness of 20mph limits and zones as follows.


20mph limits:
 Speed limit signing without supporting traffic calming
measures reduces speeds on average by 1mph.
 Research carried out by Mackie in 1996 stated that
the average speed reduction is 2mph. (Please refer
to DfT 1-6 paragraph 82).
20mph zones:
 Average speeds within zones reduced by 9mph
 Accident frequency reduced by 60%
 Overall reduction in child accidents up to 67%
 Overall reduction in cyclist accidents up to 27%
 Traffic flow within zones reduced by up to 27%.
Portsmouth Case Study:
A 20mph limit has been implemented in the City of
Portsmouth during 2008 on all residential streets. This
does not include arterial roads where the limit remains
at 30mph. Speed counts were recorded on a 10%
sample of all residential streets. The results showed that
recorded average vehicle speeds were 24mph or under
– therefore meeting central government guidance on
implementing a limit.
The limit was introduced due to the high number of
collisions within the residential area. The purpose of the
limit was to bring down the level of collisions. Anecdotal
evidence suggests that collision levels are reducing. A
full analysis will take place once the limit has been fully
implemented for one year.




DETR Circular 5/99 (1999) – 20mph
speed limits
TAL 7-91 Speed Limit Zones
TAL 9-99 20mph speed limits and
zones
TAL 12-00 Urban Street activity in
20mph zones
DfT 1-06 Setting Local Speed Limits
LTN 1/07 Traffic Calming - Section
3.2 Roads with 20 mph speed limits.
HCC PTU Quality Bus Infrastructure
in Hertfordshire – A Design Guide
May 2004.
Key Criteria
20mph Limits and Zones:
C13 - 20mph limits or zones will not be
generally considered on the primary
route network.
C14 –All requests for 20mph limits and
zones will be assessed by the Speed
Management Group against the key
criteria.
20mph Zones:
C15 - 20mph zones must be self
enforcing.
C16 - 20mph zones should have
associated physical measures which will
bring down vehicle speeds to a
maximum of 24mph, or under.
C17 - Repeater signs are not permitted
within 20mph zones.
C18 - The Passenger Transport Unit
design guide states that if a 20mph zone
is considered necessary on a bus route
the length of the zone should be kept to
a minimum so as not to adversely effect
the quality of ride.
C19 - Where possible all bus routes
should be re-routed to avoid 20mph
zones.
Limits:
C20 - 20mph speed limits will only be
considered where the recorded 85th
percentile vehicle speeds are 25mph or
less.
Nationally most 20mph zones and limits around the
country have been implemented because the collision
history is high. In Hertfordshire limits and zones have
been implemented through non-collision related funding
targets. Eg. Local Transport Plan Mode Share to School
target. See question 3 in relation to school and 20mph
limits and zones.
17
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


BUFFER ZONES
Photographs
Relevant Guidance
 DfT Circular 1-06 Setting Local Speed
Limits (paragraphs 38 – 40)
 No specific TAL leaflets
Disadvantages:
 Non-compliance can be apparent 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.
Introduction
Countdown markers can be considered on the
approach to speed limit terminal signs to
highlight to drivers that they are approaching a
lower speed limit. However current legislation
does not prescribe markers for this use.
Therefore, traffic authorities must apply for
special authorisation from DfT before they can
be installed.
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. If these
are considered, this should only be as part of a package
of measures.
C21 - Buffer zones should only be
installed where speeds in the lower
speed limit exceed the ACPO
threshold speeds. (eg. 35mph in a
30mph limit, 46mph in a 40mph limit).
C22 - Buffer zones should be no less
than 600m. In exceptional
circumstances lengths of between
400 – 600m will be considered by the
Speed Management Group.
40mph speed limit between 30mph and
50mph\derestricted speed limits
50mph speed limit between 40mph and
derestricted speed limits
COUNT DOWN MARKERS
Effectiveness / Advantages and
Photographs
Disadvantages / Case Studies
Key Criteria
Relevant Guidance
 DFT Circular 1/06 Setting Local Speed
Limits, para 65-66
 TAL 1/04 – Village Speed Limits
 LTN 1/07 section 10.2.11
Key Criteria
C23 - As count down markers need
special authorisation from DfT, any
applications shall be approved by
the Speed Management Group to
ensure a consistent approach is
adopted across the County.
18
Introduction
VEHICLE ACTIVATED SIGN ROUNDEL
A Roundel VAS 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.
(Please see section on Innovation for section on
Vehicle Activated LED Chevron Signs).
VEHICLE ACTIVATED SIGNS
Effectiveness / Advantages and
Photographs
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 of the need to slow down.
 Only gives motorists a limited amount of information
about their speed.
Relevant Guidance
 DFT Circular 1/06 Setting Local Speed
Limits, para 64
 LTN 1/07 Traffic Calming - Section 9
Vehicle activated devices
 TAL 1/03 - Vehicle Activated Signs
Key Criteria
C24 - The signing, lining and location
of exiting signs must be reviewed
prior to a vehicle activated roundel
being considered.
C25 - A vehicle activated roundel
should not be deployed unless it is
clear that fixed signing can not
remedy the problem.
C26 - 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.
C27 - When considering a vehicle
activated roundel, existing 85th
percentile vehicle speeds must
exceed the ACPO threshold speeds
(eg. 35mph in a 30mph limit, 46mph
in a 40mph limit).
C28 - Vehicle activated roundels
should generally considered as 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.
C29 - The signing and lining and
location of exiting signs must be
reviewed prior to a vehicle activated
sign being considered.
C30 - A hazard warning vehicle
activated sign should not be
deployed unless it is clear that fixed
signing can not remedy the problem.
C31 - 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.
C32 - Hazard warning vehicle
activated signs should generally
considered as part of a package of
measures.
19
SPEED INDICATOR DEVICE (permanent)
This is a vehicle activated sign that measures
and displays 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 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.
Advantages:
 Can be more informative than a speed limit roundel
 Can be applied to almost any speed limit.
Disadvantages:
 Cannot be used for speed enforcement purposes
as 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 the speedometer.
C33 - The signing and lining and
location of exiting signs must be
reviewed prior to a speed indicator
device being considered.
C34 - A speed indicator device
should not be deployed unless it is
clear that fixed signing can not
remedy the problem.
C35 - 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.
C36 - When considering a speed
indicator device, existing 85th
percentile vehicle speeds must
exceed the ACPO threshold speeds.
(eg. 35mph in a 30mph limit, 46mph
in a 40mph limit).
C37 – 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.
C38 - Speed indicator device should
generally considered as part of a
package of measures.
SPEED INDICATOR DEVICE (mobile)
The same as permanent indicator devices
except that these can be moved to different
locations as and when required.
During 2009 a trial is taking place in North
Hertfordshire with three mobile speed indicator
devices. Their effectiveness will be evaluated in
December 2009. If deemed to be successful it is
anticipated that further speed indicator devices
will be purchased across the County.
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.
C39 - A trial is being carried out by
the Police in North Hertfordshire
using three mobile speed indicator
devices. The trial will be assessed in
December 2009. If effective,
consideration will be given to using
further devices across the County for
education purposes.
Disadvantages:
 Can not 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.
20
EFFECTIVENESS OF VEHICLE ACTIVATED
SIGNS SUMMARY
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:
 Reduces mean speed 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. (LTN 1/07 Sec 9.3.1).
 In Hertfordshire vehicle activated signs have been
shown to reduce vehicle speeds by between 2 –
4mph.
 Research carried out by Norfolk County Council
showed that vehicle activated signs were more
effective in rural environments, rather than urban
areas.
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
Photographs
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
C40 - Home Zones will only be
considered where 85th percentile
speeds are under 20mph.
C41 - A Home Zone will only be
considered where the afternoon peak
flows are less than 100 vehicles.
C42 - Due to their expense, all
requests for Home Zones will be
considered by the Speed
Management Group.
21
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
Photographs
Relevant Guidance
 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
Advantages:
 Does not require any significant physical traffic
calming measures
 Is particularly appropriate for rural areas
Disadvantages:
 Effectiveness based on pilot schemes is
questionable
Key Criteria
C43 - Based on evidence collated
from previous work Quiet Lanes will
not be further implemented due to
their limited success.
National Pilot Projects:
Quiet Lanes pilots first took place in Kent and North
Norfolk. Before and after counts were carried out which
showed mixed results in terms of vehicle speeds
changes of between +0.1mph and – 2.3mph.
The monitoring 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 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 vehicles.
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.
GATEWAY & ENTRY FEATURES
Effectiveness / Advantages and
Photographs
Disadvantages / Case Studies
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:
Relevant Guidance
 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
Key Criteria
C44 - Gateway and entry features will
only be considered as part of a
package of measures to assist in the
reduction of vehicle speeds.
C45 - Careful consideration will be
given to material choices for
gateway and entrance features in
respect to future maintenance.
Effectiveness:
 TAL 1/94 section 7.4 states that:
Minor gateway treatments achieved reductions in 85th
percentile speeds which were generally below 3mph at
the gateways and below 2mph in the village.
22
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 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.
More significant treatments at gateways, speed
reductions of 6 - 7mph were attained, with reductions in
the village of some 2-3 mph.
Entry Treatment:
Major gateways relying on more physically restrictive
treatments were installed. Reductions in 85th percentile
speeds were 10mph in some cases, though within the
village 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 over taking manoeuvres.
CHICANES
Photographs
Single Lane Working Chicane:
Disadvantages:
 Driver frustration in having to wait can lead to
increase in collisions.
 Can not 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
C46 - When using single way
working, two way vehicle flows
should not exceed 3, 000 vehicles
per day and will not exceed 4, 000.
C47 – Chicanes can be used on
roads with a speed limit of 40mph or
below.
Two Way Working Chicane:
Two way working chicanes take up more
carriageway space than other 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.
23
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
Centre islands and refuges can be installed in
the middle of the carriageway to narrow the
width of the driving lane and assist in reducing
vehicle speeds. Such facilities will 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.
C48 - Pinch points will not be used in
isolation to reduce vehicle speeds –
only as part of a package of
measures.
C49 - Pinch points will not be used in
a road with a speed limit above
40mph.
Disadvantages:.
 Driver frustration in having to wait can lead to
increase in collisions.
 Can not 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
C50 – Central islands and refuges
will only be used as 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.
 Driver frustration in having to wait can lead to
increase in collisions.
24
Introduction
ROUND TOP AND FLAT TOP HUMPS
Effectiveness / Advantages and
Photographs
Disadvantages / Case Studies
Round top and flat top humps have been used
extensively across Hertfordshire. The main
difference between these features being the
rounded or flat top profile.
Advantages:
 Can effectively reduce vehicle speeds.
 Can also provide crossing points for pedestrians.
Flat top humps having the added benefit that
they can also be used as raised crossing points
in appropriate locations.
Disadvantages:
 Can cause additional noise when vehicles traverse
the features.
 Can be difficult to construct the feature at the correct
gradient.
 Can be uncomfortable for cyclists to traverse.
Introduction
Cushions are now the favoured more commonly
over road top and flat top humps.
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.
CUSHIONS
Photographs
Relevant Guidance
Key Criteria
 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
 HCC PTU Quality Bus Infrastructure in
Hertfordshire – A Design Guide May
2004
 Hertfordshire Hump Construction
Protocol
C51 - PTU design guide recommends
that these should not be less than
25m from a bus stop, also that speed
cushions are preferred to tables.
Relevant Guidance
Key Criteria
As Round Tops & Flat tops above, but also;
 TAL 1/98 Speed cushion schemes
 TAL 4/94 Speed cushions
C53 - PTU 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 - Round top humps are not
permitted on bus routes and the
primary route network.
C54 – Bolt down cushions will be
used.
Disadvantages:
 Can allow HGV’s to traverse the cushions without
the need to reduce speeds due to wider wheel
base.
25
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.
 Most affective in rural areas.
Relevant Guidance
 LTN 1/07 Traffic Calming - Section 5
Rumble devices and overrun areas
 TAL 11/93 Rumble devices.
Key Criteria
C55 – Rumble strips should be used
across the full width of the
carriageway to avoid overtaking.
C56 – Rumble strips can only be
used at least 200m from a residential
property.
Disadvantages:
 Research indicates minimal speed reduction of
around 1mph.
 Not the most appropriate traffic calming for urban
areas due to noise.
C57 – 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 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.
RUMBELWAVE 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
C58 – 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
1.9mph. 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 speed reductions were just over 1 mph.”
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Introduction
VARIABLE SPEED LIMITS
Effectiveness / Advantages and
Photographs
Disadvantages / Case Studies
Variable speed limits are most commonly used
on the motorway network during road works or
in congestion hot spots.
Introduction
Mini roundabouts assist in giving easier
access from side roads where access on to
other roads is difficult. 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
Key Criteria
 DFT Circular 5/99 – 20 mph speed limits,
para 13, Variable Speed Limits.
C59 - All requests for variable speed
limits will be considered by the
Speed Management Group.
Relevant Guidance
Key Criteria
 DMRB VolSec 6 Road Geometry
TD54/07
 HCC PTU Quality Bus Infrastructure in
Hertfordshire – A Design Guide May
2004
C60 - PTU design guide recommends
that the central dome of a mini
roundabout to be no more than
75mm, with side slopes of less than
1:20.
C61 – Mini roundabouts should only
be considered as part of a package
of measures to reduce vehicle
speeds.
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INNOVATION – New traffic calming features being trialled
Effectiveness / Advantages and
Photographs
Relevant Guidance
Disadvantages / Case Studies
Introduction
GREEN NATIONAL SPEED LIMIT
The Existing Situation:
In rural areas, when leaving a village speed
limit existing ‘national speed limit applies’
signs are usually seen. These indicate to drivers
that they are legally permitted to drive at the
national speed limit (60mph for a car on a single
carriageway road). However, this is the
maximum legal speed and the signs do not
mean it is safe to drive at this speed irrespective
of conditions.
A trial will be taking place in North Norfolk during 20092010 to trial these signs as part of Rural Demonstration
Project in conjunction with DfT. If successful the project
maybe adopted nationally and the signing given DfT
approval.

No guidance as yet whilst being trialled.
Please see The Green National Speed
Limit Fact Sheet
Key Criteria
C62 - To keep up to date on new
speed management techniques
which are being trialled nationally,
assess their success and consider
implementation in Hertfordshire
where appropriate.
C63 - To take a pro-active stance
with DfT in trialling new speed
management techniques as and
when appropriate.
The Idea:
The Green National Speed Limit Sign is an idea
for certain roads to improve awareness
amongst drivers that although the national
speed limit applies on the road, it is still a rural
country lane. As such drivers should expect
hazards associated with a rural lane (e.g.
bends, narrow road, farm vehicles, wild
animals). These may not necessarily have
warning signs and drivers should adjust their
speed according to the road character.
The Idea Would Involve:
On selected rural roads the existing
‘national speed limit applies’ signs would
need to be patched with a green chevron.
To help explain the green signs, short term
temporary posters may need to be provided
below a selected number of them.
Audits would be undertaken on the roads
signed with the Green National Speed Limit.
Sign and certain superfluous warning signs
may be removed.
Publicity and promotion would be needed to
explain the sign.
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ELECTRONIC ROAD STUDS
Awaiting results of before and after study.
No guidance as electronic road studs are
still being trialled.
Have been installed on the A1075 Ovington Bends,
Norfolk.
No guidance as chevron signs are still
being trialled.
Electronic roads studs or ‘cats eyes’ which
illuminate on approach by the driver. Studs can
be activated when vehicle approach a corner at
speed or in wet conditions.
LED INTERACTIVE CHEVRONS
LED’s in the signs are activated when the bend
is approached at speed.
Awaiting results of before and after study.
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