GB2342800A

GB2342800A - Measuring vehicle speed

Info

Publication number: GB2342800A
Application number: GB9818571A
Authority: GB
Inventors: Marek Daneshfar
Original assignee: MONITRON INTERNATIONAL Ltd
Current assignee: MONITRON INTERNATIONAL Ltd
Priority date: 1998-08-27
Filing date: 1998-08-27
Publication date: 2000-04-19
Also published as: GB9818571D0

Abstract

Images of a vehicle and markings with predetermined spacings on a road are taken at different times. A virtual measurement grid is applied to the images to determine the respective positions of the vehicle. The measurement grid is based upon the position of the marks. The distance travelled by the vehicle can therefore be derived since the time interval is known. The system may include a primary speed measuring means in order to select the time interval between capturing the two images. The image may be processed at the camera site or elsewhere.

Description

Title: VEHICLE SPEED DETERMINATION Description of Invention This invention relates to a method of determining the speed of a vehicle.

The invention has been devised for providing a secondary speed measurement system for use in conjunction with so-called"speed trap" cameras, which are widely used for the enforcement of speed limits on roads.

A speed trap camera, as is well known, comprises a primary means for measuring the speed of passing vehicles and when a vehicle is detected travelling at an excessive speed, the vehicle's speed is recorded and the vehicle photographed so that the driver can be traced from the vehicle's registration plate and appropriate action taken, e. g. the levying of a fine proportionate to the excess speed. In fact two photographs are taken with a predetermined time interval between them when a vehicle is detected to be travelling at an excess speed and the reason this is done, at least in Britain, is that for legal reasons there requires to be a secondary measurement of the vehicle's speed. Such secondary measurement is provided by marking the road with a large number of transverse lines at a known spacing, and the number of such lines which have been passed by the vehicle in the time interval between the taking of the two photographs provides a measurement of the vehicle's speed which can be used to verify the measurement taken by the primary speed-measuring means. The speed is calculated by electronic means and such speed data along with information such as the time and date is recorded on the photographs.

Whilst this method of secondary speed measurement is satisfactory, in terms of its technical performance, it presents a disadvantage in terms of the necessity to mark the road surface with a large number of transverse lines.

Typically such lines require to be provided over a fifty metre length of road surface with a two metre spacing between adjacent lines. This draws additional attention of drivers to the presence of a speed trap camera and whilst in some situations this may be desirable in causing drivers to slow down, on some roads it is undesirable as it tends to lead to traffic"bunching"which is itself a potential hazard. Also there may be some situations where the presence of the camera might be desired to be completely concealed, which is not really possible if the road surface is prominently marked.

Accordingly, it is broadly the object of the present invention to provide for speed measurement in a manner suitable for secondary speed measurement as described above, but while avoiding the above referred to disadvantages of the known method.

According to one aspect of the present invention, we provide a method of measuring the speed of a vehicle travelling over a section of road, comprising providing at least part of said section of road with a number of markings at a predetermined spacing therealong; electronically capturing a first visual image of said vehicle on said section of road and, after a time interval, electronically capturing a second visual image of said vehicle on said section of road; displaying said images; creating a measurement grid on a displayed image of said section of road, said measurement grid being based on said markings on the road and covering substantially all said section of road; plotting the respective positions of a corresponding part of said vehicle on said measurement grid for both said images; thereby determining the distance travelled by the vehicle in said time interval and calculating from said distance and time interval the speed of the vehicle.

The method according to the invention has the important advantage over the known method as above described in that the markings on the section of road which are used when the images thereof are displayed to create the measurement grid for plotting the movement of the vehicle and thus determining the distance travelled thereby in the time interval between the two captured images, can be relatively inconspicuous, e. g. dots at or near the sides of the section of road. The problems resulting from prominent marking of the section of road for secondary speed detection purposes are largely overcome.

The method may further comprise the step of measuring the speed of the vehicle by a primary speed-measuring means, and determining the interval between capture of the first and second images in accordance with such measured speed.

This ensures that the distance travelled by the vehicle in the time interval is consistent with accurate plotting of the movement of the vehicle between the first and second images thereof, to avoid, as far as possible, any inaccuracies which might occur from perspective effects if the vehicle was in an extreme position.

According to another aspect of the invention, we provide apparatus for use in carrying out the method of the invention. Such apparatus needs to comprise means for establishing a visual image of the section of road, and means for electronically capturing two of such images with a time interval therebetween; means for displaying said two images, and means for plotting on said displayed images the respective positions of the vehicle, with reference to a measurement grid created on a displayed image of said section of road. The apparatus may then further comprise means for calculating the distance travelled by the vehicle, and from said distance and time interval, the speed of the vehicle.

The above described display of the two captured images of the vehicle on the section of road with said time interval therebetween will, it is envisaged, be carried out by an operator working at a computer terminal, e. g. a PC provided with appropriate software, which is provided with transmitted data representing the captured images of the vehicle on the section of road and the time interval therebetween.

By the roadside, there requires to be provided a camera capable of providing electrical signals representing an image of the section of road, and a primary speed-measuring means for detecting when a vehicle travelling at excess speed enters said section of road so as to cause the signals representing the first and second images of the road with the vehicle thereon to be captured.

These signals (along with the time, date, and the speed measured by the primary speed-measuring means) may be recorded on any suitable storage media at the site of the camera or may be transmitted to another site. In the former case, the storage medium may be removed at intervals to another site for processing, or the information stored thereby be downloaded at intervals.

At the roadside the primary speed measuring means for initiating operation of the apparatus may be of a type which is generally known for use in connection with speed trap cameras, e. g. piezo-electric detectors. Preferably there is provided means for calculating from the speed as measured by the primary speed measuring means the desired time interval between capture of the two images of the vehicle on the section of road.

The invention will now be described with reference to the accompanying drawings, to which individual reference will be made hereafter.

Figure 1 of the drawings shows diagrammatically a section of road, specifically a section 10 of single carriageway, two-way traffic, road 10. A further road 11 intersects the road 10 and the junction therebetween may be controlled by traffic lights. In this case, the"stop"line for traffic approaching the intersection of the road 11 with the road 10, in the direction from left to right along the road 10, is indicated at 12. The disposition of a camera unit for monitoring traffic travelling in such direction is indicated at 13. The camera unit 13 contains a camera device which provides electrical signals representing an image of the section of the road within its field of vision, and such field of vision is arranged to include the adjacent side of the road 10 approaching and extending over the intersection with the road 11.

The surface of the road 10 is provided with a number of marks at a known spacing from one another. As illustrated in Figure 1, these marks comprise dots of sufficient size to be visible on the image recorded by the camera unit and such marks extend at one metre intervals from a position five metres before the"stop line"12 to a position 15 metres thereafter. Such dots in Figure 1 are shown at 14 along the side of the road adjacent the kerb and at 15 along the centre of the road.

The camera unit has associated with it a primary speed-measuring means, e. g. three sensitive strips of piezo-electric type set in the road surface a known distance apart from one another and extending transversely of the road.

There is means for measuring the time between the receipt of electrical signals from the three detectors, and for calculating the speed of a vehicle from such measured time and the known distance between such detectors. Other forms of primary speed measuring means, e. g. radar or laser detectors could be utilised.

Upon such detection of excessive speed by a passing vehicle, the camera unit is caused to record two visual images of the section of the road with a vehicle thereon at a certain time interval between such images: the time interval may be determined in accordance with the measured speed as above described.

As above referred to, such images and information as to the time therebetween may be transmitted from the camera unit to another site at which it may be stored or processed immediately, or may be stored on a memory associated with the camera unit to be downloaded to another site some future time or transmitted by physical removal of a memory element. The information is then processed as follows, with reference to the remaining drawing.

Figure 2 is a displayed image of a section of road (in this case one carriageway of a dual-carriageway having two lanes for traffic in each direction). In this case, the carriageway has a first series of markings 20 adjacent the nearside kerb, a second series of markings 21 adjacent the offside kerb, and a further series of markings 22,23 near the centre of the carriageway and corresponding to each traffic lane. A vehicle 24 is indicated at a position near the start of the section of road having the markings, which position would be expected to be that of a first image of the section of road on detection of the entry of the vehicle to the section at an excessive speed. Figure 3 shows the vehicle at a second position which, after a time interval, shows the position to which the vehicle has moved within that time. Figure 4 shows the vehicle in the latter position, but with the addition of a measurement grid of lines constructed across the image by using the mouse of a computer terminal on whose screen the image is displayed to draw lines between corresponding markings across the road. In fact the measurement grid of lines drawn in this way would usually be established by initially displaying an image of the section of road without any vehicle thereon, and when this has been done the measurement grid can be superimposed on any other corresponding image of the section of road, as viewed from the fixed position of the camera unit.

When secondary measurement of the speed of a vehicle is to be carried out, an operator, having firstly established the measurement grid of transverse lines with reference to the displayed image of the section of road, will then display the first image as Figure 2 of the vehicle in the section of road. The operator will select a clearly identifiable part of the vehicle, e. g. the point of contact of the adjacent rear wheel thereof with the ground, as indicated at 30 in Figure 2, set the cursor 31 to such point using the mouse and click on the mouse at such point.

The operator will then display, Figure 3, the second image of the vehicle on the section of road and click on the mouse with the cursor 31 positioned at the corresponding part of the vehicle in this image. This creates a vehicle movement line 32 which is shown in Figure 4 superimposed on the measurement grid.

It will be appreciated that the line of vehicle movement with reference to the measurement grid represents the distance travelled by the vehicle. Since the time between the two images, in which the vehicle travels the distance, is known, this can be used to provide a calculation of the vehicle's speed, and a secondary speed measurement as a check on the measurement carried out by the primary speed measuring means.

The spacing between the lines of the measurement grid may for example represent a distance of one metre on the road. The distance travelled by the car may be calculated by counting the number of measurement grid lines crossed by the line of vehicle movement. Counting the number of measurement grid lines crossed can be carried out either by the operator or by software.

All the above-described functions as to the establishment of a measurement grid on the images of the section of road, the plotting of a vehicle movement line thereon, the calculation of vehicle speed, together with any other required additional features, would be afforded by the provision of suitable software for these purposes.

In the example shown, although at least a pair of markings is used to define each measurement grid line, it may be envisaged that markings on the road may define only a number of the measurement grid lines, with the position of the remainder of the measurement grid being calculated from the defined measurement grid lines. Preferably the road markings would only comprise six markings per lane, two pairs of markings to define each of the end measurement grid lines and a pair of markings corresponding to the central measurement grid line to provide a check on the accuracy of the calculated measurement grid.

Figure 1 shows a section of road which includes a traffic light controlled junction. A speed measurement system in accordance with the invention may be provided in association with a system for detecting red light violations : thus detection of excessive vehicle speed may be carried out as well as the recording of vehicles passing a red light.

The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

Claims

CLAIMS 1. A method of measuring the speed of a vehicle travelling over a section of road, comprising providing at least part of said section of road with a number of markings at a predetermined spacing therealong; electronically capturing a first visual image of said vehicle on said section of road and, after a time interval, electronically capturing a second visual image of said vehicle on said section of road; displaying said images; creating a measurement grid on a displayed image of said section of road, said measurement grid being based on said markings on the road and covering substantially all said section of road; plotting the respective positions of a corresponding part of said vehicle on said measurement grid for both said images; thereby determining the distance travelled by the vehicle in said time interval and calculating from said distance and time interval the speed of the vehicle.
2. A method according to Claim 1 further comprising measuring the speed of the vehicle by a primary speed-measuring means, and determining the interval between capture of the first and second images in accordance with such measured speed.
3. A method according to Claim 2 further comprising storing signals representing at least said visual images and speed as measured by the primary speed-measuring means in the vicinity of said section of road.
4. A method according to Claim 2 comprising transmitting signals representing said visual images and at least said speed measured by the primary speed measuring means to another site for processing.
5. Apparatus for use in carrying out the method of Claim 1 or Claim 2 comprising means for establishing a visual image of the section of road, and means for electronically capturing two of such images with a time interval therebetween; means for displaying said two images, and means for plotting on said displayed images the respective positions of the vehicle, with reference to a measurement grid created on a displayed image of said section of road.
6. Apparatus according to Claim 5 further comprising means for calculating the distance travelled by the vehicle, and from said calculated distance and time interval, the speed of the vehicle.
7. Apparatus according to Claim 6 comprising a camera for providing electrical signals representing said images of the section of road, and a primary speed-measuring means for detecting when a vehicle travelling at a predetermined excess speed enters said section of road so as to cause the signals representing the first and second images of the road with the vehicle thereon to be captured.
8. Apparatus according to Claim 7 comprising means for storing said signals at the site of the camera.
9. Apparatus according to Claim 7 or Claim 8 comprising means for transmitting said signals representing said visual images to another site for processing.
10. Apparatus according to any one of Claims 7 to 9 comprising means for calculating and setting, from the speed as measured by the primary speed measuring means, the time interval between capture of said two images of the vehicle on said section of road.
11. A method of measuring the speed of a vehicle, substantially as hereinbefore described with reference to the accompanying drawings.
12. Apparatus for measuring the speed of a vehicle, substantially as hereinbefore described.
13. Any novel feature or novel combination of features described herein and/or in the accompanying drawings.