AU2002352342A1 - Traffic calming surface - Google Patents

Description

TRAFFIC CALMING SURFACE

The present invention relates to a traffic calming surface which will alert vehicle drivers to hazards ahead by creating an audible and vibratory warning inside the vehicle.

A number of traffic calming surfaces have been developed in order to alert drivers to approaching hazards, such as a junction or a pedestrian crossing, and serve to indicate to the driver that he should decelerate. Speed bumps have been widely used for a number of years and comprise a raised section which extends transversely relative to the intended direction of travel. In order to traverse the speed bump smoothly and safely, the speed of a vehicle must be reduced. A series of speed bumps positioned along a stretch of road will serve to ensure that the speed of vehicles moving along the road are regulated.

In more recent years, rumble areas/strips have been employed, particularly in rural areas, in an attempt to slow traffic approaching a potentially hazardous situation. The known rumble strips generally comprise a concrete, bituminous or synthetic surface overlay having a series of irregularities such as raised bars or an imprinted pattern of grooves . As a vehicle traverses the rumble strip, a range of vibrational frequencies are generated at the tyres which will be transmitted to the driver's cab. The vibrational effect of the strip will be felt and heard by the driver and will act as a warning that the driver should reduce his speed.

Rumble strips were originally developed in the 1970 's as a traffic calming surface for use primarily in rural areas. Ac that time, little thought was given to the external noise disturbance generated as vehicles traversed the strips when the surface was designed. One of the main disadvantages of the rumble strips currently employed on the roads is that they generate considerable noise levels outside the vehicle which has a detrimental effect on the surrounding environmen . This problem is compounded by increasing traffic volumes seen on the roads today. For these reasons, the environmental effects of introducing traffic calming surfaces into urban, residential and rural areas has become an issue. As a result of pressure imposed on Governments and local authorities by environmental agencies, there has been a considerable need to provide a means to slow traffic approaching hazardous areas, while minimising the consequential noise disturbance which may be experienced in the surrounding area. More recently, urban planners have also become interested in the need to develop a quieter means of controlling traffic.

According to one aspect of the present invention, there is provided a traffic calming surface, the upper surface of which has a continuous, substantially sinusoidal, profile which extends along the intended direction of travel.

Traffic calming surfaces according to embodiments of the present invention have been shown to generate significant interior ^'noise and vibration which will act as a warning to the driver that he should reduce his speed. Trials have also shown that -exterior noise disturbance, caused by vehicles traversing the surface, is substantially reduced as compared to the exterior noise arising from conventional rumble strip designs. Embodiments of the present invention are therefore ^■ envisaged to be particularly beneficial in calming traffic in urban and/or residential areas.

This effect can be explained by consideration of the so called forcing frequencies generated as the tyres traverse the traffic calming surface. The forcing frequency is the frequency of an oscillating force at the tyre/profile interface generated as a consequence of the wheels being forced to follow the sinusoidal profile as it traverses the traffic calming surface. A series of discontinuities, such as raised slots or an imprinted pattern of grooves, will produce a number of pulses of vibration as a car traverses them, thereby generating a wide range of frequencies which will contribute to the overall noise disturbance. Loose fitting panels can also vibrate creating parasitic noise covering a wide range of frequencies. However, a sinusoidal profile will preferably only cause one main frequency of oscillation with few higher frequency harmonics.

Advantageously, the wavelength of the continuous sinusoidal profile is approximately equal to the contact patch length of a vehicle tyre. Furthermore, it is advantageous for the wavelength of the sinusoidal profile to be in the range 0.28m to 0.48m. Preferably, the wavelength of the sinusoidal profile is in the range 0.3m to 0.4m with the optimum wavelength being 0.35m.

Preferred embodiments of the present invention have a peak to trough amplitude in the range 4mm to 12mm. Advantageously, the peak to trough amplitude is in the range 4mm to 7mm. The maximum deflection from the road surface is preferably 15mm. A traffic calming surface embodying the present invention may advantageously comprise a synthetic bitumen material such as that described in patent application no: GB 9717549.1 (Imprint C) , the disclosure of which in incorporated herein by way of reference thereto. This material comprises a synthetic bitumen formulated from binder resin, polymer and plasticiser, mixed with filler and aggregate and is particularly beneficial since it exhibits a number of advantageous properties. For example, the material may be applied to the road in a molten form and is readily moulded to the desired profile shape. Once moulded, the material is resistant to slump and is stiff enough to withhold traffic pressure but is resistant to cracking. Furthermore, as this material is generally pale in colour, it may be easily coloured by both light and dark pigments.

Alternatively, the traffic calming surface may comprise bitumen based materials such as asphalt, concrete, close graded fine aggregate or a polymer modified compound. Surfaces made from recycled molten tyres are also envisaged.

It is also envisaged that the traffic calming surface may be formed in a factory or the like; the pre-formed surface may then be secured to the road by means of bolts and/or glue and/or nails. Furthermore, the surface advantageously extends across the entire width of the road. However, narrow breaks in the traffic calming surface may be provided along the road edge for reasons of drainage or to serve d^. cycle paths.

For a better understanding of the present invention, and to show how the same may be carried into effect, reference will now be made, by way of example to the accompanying drawings in which:

Figure 1 illustrates interior noise and vibration levels experienced by a medium sized car traversing a traffic calming surface embodying the present invention;

Figure 2 illustrates exterior noise levels generated by a number of different traffic calming surfaces;

Figure 3 shows a traffic calming surface embodying the present invention;

Figure 4 shows the profile of a traffic calming surface embodying the present invention;

The dimensions of the continuous sinusoidal profile, such as wavelength and peak to trough amplitude, are advantageously chosen so as to achieve maximum transmission of tyre vibration into the driver's cab while minimising the exterior noise disturbance. There are a number of approaches which may advantageously be considered when seeking to achieve this. For instance, it is beneficial for the surface to cause significant horizontal vibrations in the vehicle suspension since, unlike vertical vibrations which are generally stifled by the vehicle suspension mechanism, horizontal vibrations are more readily transmitted to the driver's cab. Both the wavelength and the peak to trough amplitude will clearly have a significant effect on the level of horizontal vibrations generated, since these factors will govern the contact forces between the tyre and the sinusoidal surface.

Furthermore, the wavelength λ (m) of the sinusoidal surface is directly related to the forcing frequency f (Hz) on the vehicle tyre, and the vehicle speed v (m/s) , according to the following relationship:

f ^J - T λ ^Hz

The wavelength of the sinusoidal profile is preferably chosen such that the forcing frequency at the tyres of crossing vehicles will excite one, or a number of, resonant frequencies within the vehicle. Advantageously, the wavelength of the sinusoidal profile is chosen such that a low forcing frequency will be generated at the tyres. The human ear is considerably less sensitive to low frequency vibrations and, at frequencies of around 35 to 40Hz, will be 40dB less sensitive than at 1kHz where the sensitivity of the ear is approaching a maximum. Therefore, it is advantageous for the forcing frequency to be in the range 35Hz to 40Hz so that external noise disturbance is kept to a minimum. Unlike a continuous profile embodying the present invention, a series of humps or bars of similar dimensions to the continuous profile, will produce short duration impulsive forces at the tyres which theory shows can be resolved into a wide range of forcing frequencies. Some of these frequencies will be close to 1kHz and will therefore be significantly more perceptible to the human ear.

The following table represents the variation in forcing frequency with wavelength of the sinusoidal profile in accordance with the above equation. The speed of the vehicle is assumed to be 30mph (48km/h) , or 13.3m/s, which is the speed limit in many residential areas:

The frequencies generated by profiles 1 to 5 span nearly two orders of magnitude, from those close to so called "body bounce" frequencies, up to those that would excite tyre cavity resonances. Surface profile 3, having a wavelength of 0.35 m, generates a forcing frequency of 37.0 Hz which would not cause significant perceptible noise at the roadside since the human ear is not sensitive to this frequency. Profiles having a wavelength of around 0.35 metres are therefore particularly beneficial in terms of minimising the external noise disturbance.

Surface profiles 6, 7 and 8 illustrate the effect on forcing frequency of sinusoidal wavelengths that are slightly longer or shorter than the wavelength of

0.35m. These dimensions were tested using a number of vehicles of different weights and sizes. Measurements of exterior noise were taken using a Bruel & Kjaer 2144 analyser with a type 4149 microphone at 7.5m from the vehicle centre line at a height of 1.2m. Crossing speeds were also measured using a radar speed metre and ranged from 15mph to 40mph (24 to 64 km/h) . Interior noise and vibration were logged with a similar analyser. Interior noise was measured near the driver's head position and vertical vibration was measured using a type 4366 accelero eter attached to the driver's seat rail. The results of these trials indicated that, in general, surfaces with wavelengths smaller than 0.35. began to produce increases in exterior noise as a result of higher forcing frequencies being generated. While the slightly longer wavelengths did not produce a significant increase in exterior noise, they were found to be less effective at creating interior noise and vibration to alert drivers. Generally, surface profile 3 produced the highest levels of interior noise and vibration, without generating significant ^"increases in exterior noise.

Figure 1 of the accompanying drawings shows two graphical representations of an experiment to measure interior noise (Figure 1A) and vibration (Figure IB) levels for a mid sized car traversing a traffic calming surface embodying the present invention. The squares represent the noise and vibration measurements taken within the vehicle as it drives over the traffic calming surface, and the dots represent comparative noise measurements when travelling on level ground. It is clear from these figures that the interior noise and vibration levels within a vehicle are significantly increased as a result of the present invention.

The first two profiles in the following table enable a comparison to be made for a variation in peak to trough amplitude with a wavelength of 0.35m. Measurements of external noise were made, and recorded, as before and comparative measurements were also.^'-made for vehicles traversing a patterned imprinted surface and a rumble strip with a series of ridges . The measurements of exterior noise for each surface profile are shown in

Figures 2A to 2D^" of the accompanying drawings. Profile Peak to Wavelength Forcing Number trough (m) frequency at amplitude 30 mp (Hz) (mm)

6.62 0.35 37

4.14 0.35 37

7.0 deep n/a n/a pattern

15 high and n/a n/a 230 wide at 1500 spacings

Referring now to Figures 2A to 2D which show a graphical representation measurements of external noise generated in the vicinity of a number of traffic calming surfaces. Figures 2A and 2B represent noise measurements taken in the vicinity of two traffic calming surfaces embodying the present invention (profiles 1 and 2) . As a control, noise levels were also measured for a vehicle travelling along a level road surface and these measurements are shown by the dots on each of the graphs. Figures 2C and 2D represent noise measurements taken in the vicinity of vehicles traversing a patterned imprinted surface (Figure 2C - profile 3) and a rumble strip with a series of ridges (Figure 2D - profile 4) .

It can be seem from Figures 2A and 2B that there was very little increase in external noise compared to the external noise generated by a level road surface.

However, the measurements illustrate the substantial increase in noise alongside the imprint pattern and the conventional rumble strip, especially at the higher speeds . Figure 3 shows an elevational view of a traffic calming surface '10 having a continuous, substantially sinusoidal, profile 11 at the central region thereof. The peak to trough amplitude is denoted by 12 and the wavelength is denoted by 13. The leading and trailing edges 14 and 15 respectively, have been laid such they provide a gentle incline for traffic to approach the profiled section. The incline preferably has a uniform gradient over its length. In this example, the incline is designed to take the traffic from the existing surface to the height of the peak over a distance of between 3m and 5m. The surface is not drawn to scale however typical measurements would be a wavelength of 0.35m and a peak to trough amplitude of 6.5mm.

Claims (13)

1. A traffic calming surface, the upper surface of which has a continuous, substantially sinusoidal, profile which extends along the intended direction of travel .

2. A traffic calming surface as claimed in claim 1, wherein the wavelength of the substantially sinusoidal profile is 0.28m to 0.48m.

3. A traffic calming surface as claimed in claims 1 or 2, wherein the wavelength of the substantially sinusoidal profile is 0.3 to 0.4m.

4. A traffic calming surface as claimed in any preceding claim, wherein the wavelength of the substantially sinusoidal profile is 0.35m.

5. A traffic calming surface as claimed any preceding claim, wherein the wavelength of the substantially sinusoidal profile is approximately equal to the contact patch length of a tyre .

6. A traffic calming surface as claimed any preceding claim, wherein the peak to trough amplitude is 4mm to 12mm.

7. A traffic calming surface as claimed any preceding claim, wherein the peak to trough amplitude is 6mm to

7mm.

8. A traffic calming surface as claimed any preceding claim, wherein the length of said traffic calming surface is 5m to 20m.

9. A traffic calming surface as claimed any preceding claim, wherein the surface is formed from a polymer modified bitumen based compound.

10. A traffic calming surface as claimed in any preceding claim, wherein the surface is formed of a synthetic bitumen mixed with filler and aggregate.

11. A traffic Calming surface as claimed in claim 10, wherein the synthetic bitumen is formed from binder resin, polymer and plasticiser.

12. A traffic calming surface as claimed in any preceding claim, wherein the surface is formed of concrete or grout .

13. A traffic calming surface as claimed in any preceding claim, wherein the surface is pre-formed and is secured to the ground by means of bolts and/or glue and/or nails.

1 . A traffic calming surface substantially as hereinbefore described with reference to the accompanying drawings .