Safe Speed Forums

Q4.6: Will I be prosecuted if the speed limit changes as I drive under an overhead gantry?
There is sufficient time to enable drivers passing under changing speed limits on the overhead gantries to slow down safely before they reach the next gantry.

Q4.7: How do I know that the system was displaying a reduced speed limit at the time of my offence?
HADECS verifies the speed limit displayed at the time of the offence, which is corroborated by the image of the offending vehicle.

Q4.8: Who should I contact if I get a Notice of Intended Prosecution?
You should contact Kent Police in the first instance. If you receive a Notice of Intended Prosecution and the date of the offence is more than 14 days old this may be due to the time it has taken to identify you as the driver at the time of the offence, and you should contact Kent Police for any further assistance.

The definition of the delay times between the setting of the variable speed limit sign and the enforcement is laid down in "The Speedmeter Handbook (Fourth Edition) Publication Number 15/05"published by the Centre for Applied Science and Technology (CAST). It used to be HOSDB ...
In any case detected by the HADECS system or similar variable limit system the evidence provides the time between the offence and the speed limit change.
The Highways Agency have chosen to say that "there is sufficient time after a speed limit change to slow to the new limit before enforcement recommences".

Page 13 says:
5.9.2 The speedmeter shall enforce the displayed speed limit (or the National Speed Limit when none is displayed) only when:
i all the speed limit signs connected to it are correctly displaying the same speed limit, except when the hard shoulder of a motorway is actively managed and that lane may show either the same speed limit or a red X;
and
ii the speed limit has been displayed for one minute or longer. This delay shall be variable to at least five minutes.
The speedmeter shall not enforce speed in the actively managed hard shoulder when the red X is displayed. It shall operate with, and only with, all speed limit signs mounted on the same gantry, facing in the same direction and over the same carriageway, and every one of these signs fully operational.
5.9.3 Whenever the speed limit is changed, a single photograph shall be taken which will show the date in day, month and year and the time in hours, minutes and seconds when the display changed, the new speed limit set and the location code.
5.9.4 Within a variable speed limit, the time shown in photographs shall be within 10 seconds of a broadcast radio clock signal. On power up, the speedmeter shall not commence enforcement until this synchronisation has been established. Enforcement shall stop whenever synchronisation is not maintained or is not confirmed with the radio clock within 14 days.

Page 24 point 8.7 states : Variable speed limit signs
8.7.1 When using a variable speed limit sign or a simulator of the sign connected to the speedmeter, the following fault conditions shall be simulated while a speed measurement of 90 mph is simulated:
i failure of any bulb used to illuminate any part of the speed limit aspect;
and
ii power up of any extra bulb or bulbs used to illuminate other speed limit aspects and not used in the correct display.
No enforcement shall occur while these fault conditions are simulated.

Speed limits4.—(1) Subject to paragraphs (4) and (5) below, where a motor vehicle being driven on any part of the relevant roads on any occasion passes a speed limit sign (“the sign in question”) no person shall, during the relevant period, drive the vehicle on any part of the relevant roads at a speed exceeding the relevant speed.
(2) For the purposes of paragraph (1) above, the relevant period is the period that begins immediately after the vehicle passes the sign in question and ends immediately before one of the following events occurs thereafter, namely—
(a)the vehicle passes a traffic sign which indicates that the national speed limit or any other specified maximum speed limit is in force; or
(b)the vehicle goes outside the area comprising the relevant roads.
(3) For the purposes of paragraph (1) above, “relevant speed” means the speed limit indicated by the sign in question at the time that the vehicle passes it.
(4) If—
(a)a motor vehicle being driven on any part of the relevant roads passes a speed limit sign at a particular location; and
(b)apart from this paragraph, the vehicle would be subject to a speed limit by virtue of this regulation, but would not have been subject to a speed limit by virtue of this regulation had it passed that location ten seconds earlier than was in fact the case,
the vehicle shall not be subject to any speed limit by virtue of this regulation.
(5) If—
(a)a motor vehicle being driven on any part of the relevant roads passes a speed limit sign at a particular location; and
(b)apart from this paragraph, the vehicle would be subject to a speed limit by virtue of this regulation, but would be subject to a higher speed limit by virtue of this regulation had it passed that location ten seconds earlier than was in fact the case,
paragraph (1) above shall have effect in relation to the vehicle as if it had passed that location ten seconds earlier than was in fact the case.

Q4.8 - This seems to be dismissing the 14 day procedure, which as far as I am aware has been standard practice for a very long time. So how long has this been extended to ? 16 days? 21days?

If you receive a Notice of Intended Prosecution and the date of the offence is more than 14 days old this may be due to the time it has taken to identify you as the driver

No over-the-road speedmeter can achieve Home Office Type Approval unless it meets the definition for the delay in the Speedmeter Handbook.

They have always been able to extend the 14 day rule if the driver was not the registered keeper.

So how exactly do they test that ?

it is a trivial matter to set up a logical timed interlock It would also be trivial to test that in a road test.

If it is so trivial, would you be so kind as to describe this "logical timed interlock"?

Is it within the camera logic on the gantry or would this be done remotely? If remote, what measures are in place to ensure sub-second accuracy in the timing. Is a log-file maintained, recording the exact time a limit is reduced, the expiration of the timeout and any violations within that period (again, to sub-second accuracy). What anti-tamper measures are implemented in any log-files?

mb

Boomers questions of 10sec timings seem fair - and not IMO answered by your replies to ed_m's questions - yet.
If you don't know the full answer or to this level you can just say of course.

There is no rubber stamping after a mathematical analysis.

The process involves a scientific analysis and then, when that suggests the system may provide satisfactory evidence it is passed to ACPO for testing in a practical situation.

I don't see the need to amplify on what has been previously explained when that amplification is required because of either laziness, ignorance or both.

The evidence

...contains the timing between the sign changes and the evidence/offence. There is no reason to further verify the evidence when the evidence contains relevant measurements. There is a large buffer period; one minute minimum, so what's the problem that the enquirer has sought to raise when there isn't one. ed-M and boomer's questions are not worth replying to as their answer is in the text above. The evidence is in the picture.