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Information from the London Borough of Sutton

Traffic management

Traffic calming and management measures

Please use our online enquiry from if you would like to know more about, or report a problem with traffic management in Sutton.

The following information has been produced to give a brief overview of a variety of traffic calming and traffic management measures available to the Council, as the Highway and Traffic Authority, to introduce on the public highway.

Traffic calming measures 

These are intended to reduce vehicle speeds, thereby reducing the number and severity of road traffic accidents, and to discourage drivers from cutting through residential side roads.

Traffic management measures

These are measures, which actually restrict traffic movement, often by physical means. These measures require the introduction of Traffic Management Orders to be legally enforceable by the Police.

Some of the options commonly used are: 

Traffic calming - speed cameras 

London Safety Camera Partnership (LSCP) is responsible for installing and operating speed cameras in London under strict guidelines. To qualify for LSCP to install speed cameras there must be a collision history of 4 'killed or seriously injured' collisions (KSI) in the most recent 36 months period, 2 of which must be speed related.


  • Self enforcing and visible
  • Popular with 90% support as a means of reducing speed 
  • Proven 50% reduction in casualties at safety camera sites installed by LSCP. 


  • Expensive
  • Not practical for all roads 
  • Perceived by some as a means of raising funds.
  • Less or no effect beyond the camera
  • Are subject to vandalism
  • Require regular maintenance

Traffic calming - central island refuge

Installation of traffic islands along the centre of the roads is generally used as a speed reducing measure as well as providing a pedestrian refuge facility to cross the road.  


  • Can provide a pedestrian facility where it is not possible to install a formal crossing.
  • Can be used to narrow the carriageway and prevent overtaking especially when used in a series, linked with centre hatching.
  • Do not affect the emergency services.
  • Can provide a protected right turn lane at junctions.
  • Provides protection to the adjacent lane


  • Limited speed-reducing effect compared with vertical deflection.
  • Loss of on-street parking.

Traffic management - mini-roundabout


  • Breaks up the flow of ‘through traffic’, thereby slowing traffic on all approaches to the junction.
  • May improve turning movements into and out of minor roads.


  • May not be effective in reducing speed of traffic if no deflection is possible.
  • The improvement of turning movements may serve to encourage more traffic onto side roads.
  • If no islands were installed, pedestrians would find it difficult to cross the junction.
  • Does not facilitate for pedestrians to cross the road; they may find it difficult to negotiate the junction safely if no traffic islands are installed.

Traffic calming and management – priority give-way (with priority provision for cyclists)


  • Utilise horizontal rather than vertical deflection so do not affect emergency services.


  • Does not significantly reduce vehicle speed unless the chicane is tight i.e. the stagger is short; this is not possible to achieve where lorries and buses still need to use the road.
  • Some drivers see chicanes as a challenge and accelerate to get through.
  • Expensive to construct, especially if drainage works are necessary.
  • Large loss of on-street parking.

Traffic calming - junction table or entry treatment


  • More acceptable to emergency services and bus operators than standard humps.
  • Slows down all approaching traffic to all arms of the junction.
  • Can be used in isolation – they do not have to form part of a series of road humps.


  • Expensive to construct.
  • Construction may cause temporary traffic disruption.
  • Often requires temporary road closures.
  • If constructed at footway height this can lead to confusion between motorists and pedestrians as to who has right of way

Traffic calming - road narrowing (throttle)


  • Interrupts through traffic movement thereby reducing speed.
  • Does not delay emergency service vehicles or affect bus operation.
  • Cycle gaps can sometimes be incorporated.
  • If cycle gap is not provided they can make safer crossing places for pedestrians.


  • Limited speed-reducing effect (some vehicles actually increase speed to get through the narrowing before an oncoming vehicle).
  • Expensive if drainage works are necessary.
  • Loss of on-street parking.

Traffic calming – round or flat top hump


  • Reasonably inexpensive to install. 
  • Minimal disruption to traffic during construction & no loss of on-street parking.
  • Proven to be effective at reducing vehicle speeds.


  • Result in an increase in emergency service response time.
  • Unsuitable on bus routes unless 65mm or lower.
  • Claims of increased noise and pollution, damage to vehicles and discomfort to occupants (but only if taken at an inappropriate speed).
  • If a flat top hump/speed table is constructed kerb to kerb at footway height this can lead to confusion between motorists and pedestrians as to who has right of way.
  • Humps with block-work tops and/or those that span kerb to kerb are much more expensive to construct, and can have drainage difficulty if constructed kerb to kerb.

Traffic calming - speed cushions (pillow hump)


  • Accepted by emergency services.
  • Accepted by bus operators.
  • Inexpensive to construct. 
  • No loss of on-street parking.
  • Cyclists can pass between cushions.


  • In a case of two cushions, if on-street parking occurs vehicles may not be able to straddle the cushions thereby negating the benefits to the emergency services and buses.
  • Yellow line restrictions may be required to protect the cushions so that vehicles can straddle them, this would then result in a loss of on-street parking.
  • Less effective at speed reduction than conventional speed humps

Traffic calming Vehicle Activated Sign (VAS)

The VAS signs were initially designed to display the speed limit when approached in excess of the speed limit, with a flashing ‘SLOW’ message to inform the driver of their excess speed. There are different types of Vehicle Activated Signs that currently are being used displaying other messages such as the speed of the approaching vehicle; or a bright smiley face when approached below the speed limit and a red angry face if the approaching speed is in excess of the speed limit, etc.

The VAS signs may also be accompanied by ‘wig wags’ (flashing amber lights) that are installed near schools, to make the sign more prominent. 


  • Simple, clear and easy for motorists to understand
  • Suitable for a wide range of locations & installation types
  • Can be set to display different speed limit, increasing their flexibility
  • Useful in areas with a persistent speed problem
  • Can be large, prominent and highly visible


  • Expensive to install
  • Needs regular maintenance
  • Does not give motorists the reason of the need to slow down
  • Needs a dedicated mains power supply 
  • Can be visually intrusive 

Traffic calming - 20mph zone

At present such a zone can only be designated where it can be proved that average speeds have been reduced to below 24mph.  A 20mph zone should be self enforcing and effective, therefore it would be necessary to install traffic calming measures within the zone. 


  • Can include any of the different forms of the traffic calming measures; therefore easier to overcome localised site restrictions.   
  • Reduction in the amount of signing required. 
  • Regular and repeated traffic calming measures will assist in maintain low and steady speed throughout the zone.


  • Requires traffic calming measures and this is not always popular with some residents
  • Difficult to control and enforce without traffic calming measure

Please use our online enquiry from if you would like to know more about, or report a problem with traffic management in Sutton