Request ID: FOI-4772-2324 Date published: 19 April 2024
You asked
Dear Transport for London,
Please provide a detailed plan showing the drainage system along the A20 from the northern end of the flyover at the A224 junction to the GLA boundary some way beyond the BP petrol station.
This to show the location of each drain / gully, and the system of linkage between them.
.
On site observation confirms there is a deep drain under the central reservation a short distance before the BP petrol station offslip.
There are also several drains / gullies further uphill.
There is a large area of soft soil between the two carriageways.
It appears some of this has washed along the road.
Is this related to the road flooding which TFL claim makes the 40mph speed limit necessary?
Elsewhere, the central reservation is raised and solid.
This prevents any build-up of water there, and any washing of soil and dirt into drains.
Will TFL replace the soft centre area with raised hard surfacing?
.
What is the schedule for ensuring this drayage system is working properly and not blocked?
Please provide a list of each date since the start of 2023 when this drainage system was checked and cleared if necessary.
.
On site observation confirms there is currently no blockage, and water can flow deep under the road.
Please provide dates since the start of 2023 when significant flooding was obscured on this entire length of road. Include on the map the locations with dates of each instance of this flooding.
Why did TFL impose a 24-7 40mph limit, when any need for this only applies for a short period of time when serious flooding is taking place?
An advisory speed limit when there was serious flooding would much better reflect any hazard, and be more appropriate and sensitive to public opinion than a 24-7 mandatory limit imposed for months on end.
Please provide the analysis that this was necessary, rather than using variable messaging signs to provide an advisory 40mph limit when serious flooding is present.
.
Given that there has been no significant flooding during March, and the drainage system appears to be working correctly, why is the 40mph speed limit still in place?
We answered
TfL Ref: 4772-2324
Thank you for your request received by Transport for London (TfL) on 23 March 2024 asking for information about the A20.
Your request has been considered in accordance with the requirements of the Environmental Information Regulations and our information access policy. I can confirm that we hold some of the information you require. Your specific questions and our replies are as follows:
Please provide a detailed plan showing the drainage system along the A20 from the northern end of the flyover at the A224 junction to the GLA boundary some way beyond the BP petrol station.
This to show the location of each drain / gully, and the system of linkage between them.
The attached plan shows existing and proposed drainage for the critical section of the A20 where remedial works are proposed.
On site observation confirms there is a deep drain under the central reservation a short distance before the BP petrol station offslip.
There are also several drains / gullies further uphill.
There is a large area of soft soil between the two carriageways. It appears some of this has washed along the road.
Is this related to the road flooding which TFL claim makes the 40mph speed limit necessary?
In the section from the BP garage up the hill, the material in the central reserve has built up over a number of years and blocks the flow path of water to the existing drainage system. The below ground pipe work was surveyed and is in reasonable condition; the drainage design which is being finalised will level the ground between the carriageways and install additional gullies. These changes are intended to remove more water from the highway surface and reduce the potential for silt build ups. We are also reviewing the maintenance regime to prevent long term silt build up.
Elsewhere, the central reservation is raised and solid.
This prevents any build-up of water there, and any washing of soil and dirt into drains.
Will TFL replace the soft centre area with raised hard surfacing?
Please refer to our answer to point 2 above.
What is the schedule for ensuring this drainage system is working properly and not blocked?
An enhanced gully cleansing regime is in place for the A20 through this section, with cleaning taking place every 6 months (the standard frequency is two years). Our driven safety inspections are carried out every 7 days, during which any evidence of drainage issues would be reported and addressed by our contractor.
Please provide a list of each date since the start of 2023 when this drainage system was checked and cleared if necessary.
Gully cleansing was last undertaken in December 2023 by our maintenance contractor under an enhanced gully cleansing regime. Prior to this gully cleansing was undertaken under our cyclic maintenance schedule in October 2022. These are normally carried out on a 2 yearly cycle, so the next clean would have been October 2024. However as we now have an enhanced gully cleansing regime for the A20 through this section, the last clean was undertaken in December 2023 and the next clean scheduled for June 2024. The weekly driven safety inspections did not identify any drainage defects for action during 2023.
On site observation confirms there is currently no blockage, and water can flow deep under the road.
Please provide dates since the start of 2023 when significant flooding was obscured on this entire length of road. Include on the map the locations with dates of each instance of this flooding.
An advisory speed limit when there was serious flooding would much better reflect any hazard and be more appropriate and sensitive to public opinion than a 24-7 mandatory limit imposed for months on end.
Please provide the analysis that this was necessary, rather than using variable messaging signs to provide an advisory 40mph limit when serious flooding is present.
Given that there has been no significant flooding during March, and the drainage system appears to be working correctly, why is the 40mph speed limit still in place?
Information on this point can be found in a previously answered request which is published on our website at the following link: https://tfl.gov.uk/corporate/transparency/freedom-of-information/foi-request-detail?referenceId=FOI-3994-2324. TfL have had to temporarily introduce a 40mph speed limit on the A20 Sidcup Road owing to ongoing surface water flooding and water sheeting which has caused a number of safety concerns. This presents a serious risk to road users and the reduced speed limit will stay in place until permanent drainage measures can be installed
If this is not the information you are looking for, or if you are unable to access it for any reason, please do not hesitate to contact me.
Please see the attached information sheet for details of your right to appeal as well as information on copyright and what to do if you would like to re-use any of the information we have disclosed.
Yours sincerely
Sara Thomas FOI Case Management Team General Counsel Transport for London
