Speed Limits and Reduction
Speed limits are assessed in terms of three main criteria as
specified in guidelines set by the
Department for
Transport . These are visual appearance and character
of the road and environment, measured vehicle speeds and personal
injury accidents.
One of the main factors to consider is measured speed. The
85th percentile is the standard used when analysing
vehicle speeds and is the speed at or below which 85% of traffic
travels under free flow conditions. If speeds are more than 20%
higher than a proposed speed limit, then evidence suggests that
introducing the speed limit will have little effect on actual
vehicle speeds without considerable enforcement.
The purpose of speed limits is that they should be
self-enforcing. They should be lowered only when a consequent
reduction in vehicle speed can reasonably be expected. There is
little point in establishing a limit, however desirable from an
environmental or safety point of view, if it is not going to have
any effect on actual vehicle speed. The introduction of unrealistic
speed limits should be avoided as the effectiveness of speed limits
generally can be compromised and consequently brought into
disrepute.
Accidents are a factor determining the necessity of imposing a
limit. Limits may be introduced because of a poor accident record,
however it is not automatic that a lowered speed limit is the best
solution. In some instances a particular accident problem might be
better met by a local safety scheme; conversely the lack of an
accident history should not in itself rule out the introduction of
a limit.
Where measured speeds are sufficiently low, a 20mph speed
limit may be introduced with no traffic calming measures. These are
indicated by terminal signs at the start and end of the limit and
repeater signs at regular intervals. Unless the road layout or
surrounding area naturally slows down traffic, these can rely
heavily on Police enforcement and are therefore more uncommon than
20mph zones.
20mph zones must include speed reducing measures at certain
intervals to enable them to be self-enforcing. No repeater signs
are required. They are, however, strictly regulated; areas must be
residential or in a busy town and existing 85th
percentile traffic speeds must be a maximum of 27mph otherwise
limits are likely to be ignored.
Advantages:
- Improves road safety;
- Very good at reducing vehicle speeds;
- Traffic calming measures situated in a 20mph zone need less
signing and street lighting than usual, which keeps visual
intrusion to a minimum.
Disadvantages:
- Requires traffic calming measures which have their own
disadvantages;
- Very expensive;
- Legislation restricts the size and location of 20mph
zones.
Speed Reducing Measures
Many requests are received from residents to reduce speeds and
improve safety.
“Traffic calming” and other speed reducing measures can have a
very positive effect on a road, however, in some circumstances,
measures introduced to solve a problem in one road, can result in
problems in adjoining roads.
Whenever any traffic management measures to reduce speeds are
proposed, careful consultation has to take place with the Police,
Fire Brigade and Ambulance service as these measures can increase
attendance times for emergency calls thus risking the lives and
property of local residents. These measures can also cause
discomfort and possible injury to passengers.
Effective traffic calming schemes are made up from a
combination of measures, designed to meet the specific targets
required for the area in question. There are a number of measures
that we can use to minimise disruption and maximise speed
reduction:
Pillow or Cushion Humps/Pads
These pads are a method of slowing narrow wheel base vehicles
such as cars, but causing minimal inconvenience to larger vehicles
such as buses and fire engines. They require special authorisation
from the Department for Transport before they can be used.
Advantages:
- Reduces vehicle
speeds;
- Improves road
safety.
Disadvantages:
- On-street parking
causes problems;
- Can cause problems
to some ambulances;
- Signs, street
lighting and white lines are required which may be considered
visually intrusive.
These are features that reach across the entire length of the
road and are strictly regulated. They must be between 50mm and
100mm high and at least 2.75 metres long, covering the full length
of the road. They may have either flat or round tops.
Eastleigh, along with most other local authorities has adopted
the 75mm high hump as standard; this reduces speeds to around 22
mph. The 100mm high humps reduce speed to approximately 17mph on
the hump but due to the delay travelling over the hump, speeds tend
to rise to 35mph between them. This causes excessive accelerating
and braking and therefore increased pollution.
They can often lead to complaints about increased noise and
vibration from traffic.
Advantages:
- Very good at reducing vehicle speeds and improving road
safety;
- Relatively cheap;
- Self enforcing;
- Do not usually affect on-street parking.
Disadvantages:
- Can cause damage to some vehicles;
- Can increase traffic noise especially when HGV’s pass by;
- Signs, street lighting and white lines are all required and may
be visually intrusive;
- Can cause discomfort for drivers and passengers;
- Can cause problems for emergency services and buses.
Junction Tables
These are large flat top humps constructed across junctions to
reduce the speed of approaching vehicles. They also provide a level
place for pedestrians to cross.
Advantages:
- Reduce vehicle speeds at junctions;
- Highlights junctions to motorists;
- Provides level crossing point for pedestrians.
Disadvantages:
- Vehicles may drive onto footway;
- May cause problems for buses;
- Pedestrians may not take care crossing them.
Mini-roundabouts
These are used both as a means of reducing accidents (by
slowing traffic) and aiding right turning movements. Their main
advantage is they can often be made within the existing roads space
eliminating the need for substantial road widening.
They are only used on roads with an average speed of 30mph or
less and are often only marked out with white paint. These may be
used as a speed-reducing feature before a series of road
humps.
Advantages:
- Can reduce driver delays when emerging from minor roads;
- Reduces vehicle speeds and can improve road safety.
Disadvantages:
- Not ideal for cyclists;
- Signing, street lighting and white lines are required and may
be considered visually intrusive;
- Can generate traffic conflicts, especially at four armed
junctions.
Chicanes and Pinch Points
These reduce vehicle speeds by reducing the amount of
available carriageway. Chicanes are constructed on one side of the
road, introducing a physical deflection into the oncoming vehicles
path, whilst pinch points narrow the road centrally. They are
frequently used to provide a safe crossing point for
pedestrians.
Advantages:
- Reduces vehicle speeds and can improve road safety;
- Well accepted by bus companies and the emergency services.
Disadvantages:
- Can reduce on-street parking;
- Can create conflicts between vehicles;
- Increase in air pollution due to stopping and starting of
vehicles;
- Usually illuminated by bollards, street lighting, signing and
white lines as all are required, which may be considered visually
intrusive.
Gateways
Gateways are installed at entrances to towns and villages or
where there is a change in character of a road, often combined with
a reduced speed limit. It shows drivers the nature of the road has
changed and encourages them to slow down. Usually, they comprise of
a mixture of warning signs, coloured/textured surface materials,
speed tables, entry treatments, planting etc.
Advantages:
- Highlight speed limit changes;
- Remind drivers of the change in road environment;
Disadvantages:
- Other measures are needed to maintain speed reduction;
- Not effective in reducing speeds over a long stretch of
road.
Road Surface Changes
These can be different colours and textures to highlight
particular features. A change in colour of surfacing can be used to
highlight an approaching hazard such as a bend or a lowered speed
limit. Alternatively, textured anti-skid surfacing can be used on a
bend itself, if skidding at such a point is a known problem.
Advantages:
- Does not reduce parking;
- Highlights certain features to road users;
- Relatively low cost;
- Does not disadvantage buses or emergency vehicles.
Disadvantages:
- Difficult to see in poor weather conditions;
- Colours can fade;
- Limited effectiveness;
- Can create confusion regarding priority.
Kerb Build Outs
These can help improve visibility at road junctions, where the
visibility is sometimes reduced due to the alignment of the road or
due to parked vehicles. Building out the kerb into the carriageway
can help solve this problem by providing protection for motorists
emerging from a side road allowing them to pull further out thereby
increasing visibility. Pedestrians are also protected as they have
more space to stand and can be seen more easily. Parked cars are
forced to park further from a junction or crossing point.
Advantages:
- Restricts traffic speeds;
- Reduces crossing distance;
- Provides additional space for pedestrians on the footway;
- Can deter unsafe parking on the junction.
Disadvantages:
- May be hit in poor weather or at night;
- Can cause difficulties for cyclists;
- Usually need bollards to stop cars driving onto them;
- Can make manoeuvres difficult for large vehicles.
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Page Last Updated: 12/19/2006
Eastleigh Borough Council
legal disclaimer
Website Comments: webmaster@eastleigh.gov.uk
Eastleigh Borough Council, Civic Offices, Leigh Road, Eastleigh, SO50 9YN
Telephone: 023 8068 8068, Fax: 023 8064 3952, Text: 07797 877001
Email:
direct@eastleigh.gov.uk