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Traffic calming

As the local highway authority, we're committed to reducing casualties on our highway network. To do this, there are traffic calming measures in place on our roads.

We receive many requests for traffic calming measures, but we have limited funding available for such schemes.

Our funds must therefore be targeted at areas where they'll be most effective. We take a number of different factors into account, such as:

  • areas with the greatest history of speed-related collisions resulting in personal injury
  • the pattern and severity of the collisions

Sites of concern are identified in a number of ways. These can be from data analysis (such as speed surveys and collision history), or reports from members of the public.

Measures can only be introduced at locations where there's an identifiable problem (such as a trend in collisions) and will be chosen based on how likely the road's safety will be improved.

The enforcement of speed limits within the county is the responsibility of the police and any instances of excess speeding should be reported to them, for appropriate action. You can contact the police on, tel: 101.

The speed-reduction measures we can consider, given the right circumstances, include road humps or speed cushions, build-outs, and chicanes. These are costly and generally not well supported by the public and so we'll tend to consider less intrusive measures where possible.

Humps, tables and cushions

These measures can only be introduced on roads with a speed limit of 30mph or less, and where street lighting is present. We have to follow the Highways (Road Humps) Regulations 1999 which state that humps are to:

  • be between 25mm and 100mm high
  • have a minimum length of 900mm
  • be either curved or flat topped, and
  • be spaced at between 20m and 150m

There will need to be very clear justification on the grounds of road safety for any of the following measures to be introduced as they're not well supported by the public.

These measures can create a level of noise and vibration for local residents. The need for associated signage and street lighting can also be considered detrimental to the aesthetic of residential areas. Given the lack of support, less intrusive measures may be more appropriate in most situations where traffic calming is needed.

Road humps

Road humps (sometimes known as 'sleeping policemen') can be used to reduce traffic speeds and discourage drivers from taking shortcuts on residential roads.

A road hump is rarely introduced on its own, and a scheme would normally include several humps, set at regular intervals, in order to reduce speeds consistently over a given route.

Speed cushions

A variation on the road hump is the speed cushion. Unlike road humps, speed cushions form small plateaux across the width of the carriageway with gaps in-between.

It's sometimes argued that speed cushions aren't as effective as road humps. They do, however, allow wider vehicles (such as ambulances) through more effectively as they can straddle either side of the plateau. Speed cushions are a useful alternative to road humps on busy bus routes and routes with lots of heavy goods vehicles.

Speed tables

Speed tables take the form of single, raised 'table-top' plateaux across the width of the carriageway. In addition to achieving reductions in speed, tables can also provide a safer crossing place for pedestrians, across the top of the plateau, where traffic speeds will be at their lowest.

Build-outs, chicanes and priority narrowing

The benefit of these measures is that vehicles don't have to travel over a physical feature, so problems of excess noise and vibration are removed.


Chicanes use features to either narrow the carriageway, allowing for 2-way traffic flow at slower speeds, or they can give priority to drivers travelling in a certain direction, creating a break in traffic flow and reducing speeds.

Chicanes can be formed by creating footway build-outs, widening of the footway into the road. This provides improved visibility for pedestrians who want to cross the road. This is of particular advantage on residential roads with high levels of parked cars.


Build-outs introduced in isolation wouldn't necessarily be used as a speed-reducing technique but the ‘narrowing’ of the road will encourage some drivers to reduce their speed. A number of build-outs, introduced at strategic locations, will create a chicane effect and help to control traffic speeds along the route in question.

Build-outs can be difficult to put in place where there are many private driveways to restrict their positioning.

Priority narrowing

Priority narrowing is usually created through footway build-outs, extending into the carriageway to such a degree as to limit it to one-way traffic flow.

The effect of this is that vehicles travelling in one direction have to give way to oncoming traffic, creating a break in traffic flow and reducing speeds.

This measure does rely on oncoming traffic to be effective. A steady flow of traffic in either direction is needed and, if the balance isn't right, can result in drivers speeding up to get through the gap first.

Footway build-outs and priority narrowing are often viewed as too intrusive by residents due to the kerbing required and the signing and lighting of the priority system.

A consequence of all forms of narrowing and build-outs is that it reduces the length of on-street parking. This is unfavourable in areas where parking space is in high demand.

Less intrusive measures will be considered wherever possible.

As with humps, tables and cushions, chicanes, build-outs and narrowing can only be introduced on roads with a speed limit of 30mph or less, and where street lighting is present.

Vehicle activated signs (VAS)

VAS have become a popular, effective, less intrusive form of speed-reduction which can be used as an alternative to more physical measures.

These are electronic signs which display a symbol or message when triggered by a vehicle travelling at a specific speed. This speed is usually set at 10% plus 2mph above the speed limit (for example, 35mph in a 30mph limit).

They're often introduced to supplement rather than replace traditional signing and lining and are aimed at addressing specific road safety problems.

Both permanent and temporary VAS measures have been used in Derbyshire. Research shows that the effectiveness of permanent VAS reduces as motorists become familiar with them.

The advantages of a temporary VAS is that it can be moved around between a number of sites; remaining at one site for a number of months before being moved to another site once motorists have become familiar with it. The sign can then be redeployed to the same site several months later to retain its effectiveness.

VAS have been used in Derbyshire to address not only problems of speeding, but also to encourage drivers to approach hazards – such as bends or junctions – at a safe speed, and to provide hazard warnings where conventional signing alone hasn't been effective. Analysis has shown that, where these signs have been introduced they've resulted in immediate and ongoing reductions to the number of accidents.

There are still relatively few signs of this nature in Derbyshire and there are concerns that to introduce them on a widespread basis would cause drivers to become used to them and reduce their effectiveness. Because of this we apply a stringent set of criteria to each application we receive, to guard against overuse and to make sure that signs are introduced where they're most needed.

VAS criteria

To prioritise our investment in VAS and to inform other bodies about where signs will be deployed or refused, all of the following criteria must be met:

  • VAS should be considered at sites that have a collision history associated with inappropriate speed, or a hazard, that hasn't been remedied by standard signing. Other signing must have been tried and have failed; the site must have been subject to a recent speed survey to determine justification for a VAS installation
  • VAS displaying a speed limit should be located at sites which have a history of a minimum of 6 injury collisions within 1km over the previous 3 years, and where speed has been a factor in some, if not all the collisions
  • VAS displaying a speed limit should be located at sites where the results of traffic surveys show the 85th percentile speed is at least 10% over the speed limit plus 2mph, measured over a 7-day period (the 85th percentile is the speed at which up to 85% of the traffic is travelling)
  • hazard warning VAS should be located at sites which have a history of a minimum of 6 injury collisions within 1km over the previous 3 years, and where the hazard has been the cause
  • the flexibility of temporary VAS means they are the preferred option but the decision on which type of VAS to be used should be made on a case by case basis. To retain effectiveness, temporary VAS should remain on site for no longer than 3 months and should not be redeployed at the same site within 6 months

Requests for VAS that meet these criteria will be prioritised on calculated estimates of the reduction in casualties.

Road markings

Before using any of these measures, we normally consider whether road markings could be used at sites which suffer from a poor road safety record. The use of road markings can be a cost-effective measure in resolving certain speed-related injury problems.

An example of road markings we may consider are rumble strips. These would normally take the form of slightly raised strips, set across the entire width of the road, and in a different colour to the road surface. The strips cause vibration when driven over to alert drivers to reduce their speed and are typically used to draw attention to a change in speed limit – for example, at the entrance to villages where there have been road accidents.

Due to the noise generated by rumble strips, we can't introduce them within 200 metres of residential properties.

Another technique we may adopt is visually narrowing road markings, usually taking the form of white hatching placed down the centre of the carriageway. This creates a visual effect of narrow traffic lanes, reducing speeds and keeping opposing vehicle flows away from each other. They also encourage lower speeds when overtaking cyclists or parked vehicles. 'SLOW' road markings can also be considered at problem locations.


For general enquiries about traffic calming measures please contact: