Request ID: FOI-1361-2122 Date published: 19 October 2021
You asked
My Freedom of Information Request concerns the volume of traffic using the Hogarth Flyover at Hogarth roundabout on the A316 in Chiswick.
Could you please tell me what volume of traffic the flyover was originally designed to carry, whether and when that has changed since its original construction and what the current limit's are for cars/vans per hour using the flyover?
Also could you tell me when the volume of traffic using the Hogarth Flyover was last measured and what the results were in terms of cars/vans per hour at peak times?
Do you have any plans to re-measure the volume of traffic using the flyover and if so when?
Finally, do you have any plans to replace the current flyover?
We answered
TfL Ref: 1361 - 2122
Thank you for your request received by Transport for London (TfL) on 24 September 2021 asking for information about traffic volumes using the Hogarth Flyover at Hogarth roundabout on the A316 in Chiswick.
Your request has been considered in accordance with the requirements of the Freedom of Information Act and our information access policy. I can confirm that we hold some of the information you require.
By way of background, in 2014 we invested in refurbishing the flyover to ensure its ongoing structural integrity and safety. This secured the flyover’s ability to safely carry traffic for a further decade while plans to remodel the Hogarth junction were being developed. The existing deck was demolished and replaced by new pre-cast concrete units; the new deck ensures cars can continue to use the flyover safely and provides a 2.5m wide single traffic lane. The flyover has a 3 tonne weight restriction for operational reasons and has a 2m width restriction at the access ramp, which physically helps to enforce the weight limit. It is legally considered a ‘weak bridge’ because it has not been designed to carry 40 tonne vehicles.
Safety is our number one priority and the structure is subject to regular Principals and General Inspections as part of our Structures Inspection programme to ensure safe operation. The last Principal Inspection was carried out in January 2020 and showed that the condition of the flyover at present is not of concern. A General Inspection is planned in our 2021-22 programme.
Answers to your specific questions are below:
Could you please tell me what volume of traffic the flyover was originally designed to carry, whether and when that has changed since its original construction and what the current limits are for cars/vans per hour using the flyover?
The flyover was constructed in the late 1960’s / early 1970’s which is more than 30 years before TfL as a transport authority was formed therefore we don’t hold information on the volumes of traffic that the flyover was originally designed to carry.
It is possible that the London Metropolitan Archives may hold some information around this as they hold some Greater London Council Engineering Archive files. We can say however that the structure has been designed to support loads which equate to the effects of all permitted vehicles less than or equal to 7.5t so is more than adequate to carry vehicles restricted to 3t and less by the width and weight restrictions in place at the structure.
Also could you tell me when the volume of traffic using the Hogarth Flyover was last measured and what the results were in terms of cars/vans per hour at peak times?
The data attached is a survey of Hogarth Roundabout from 2013. This is the most recent survey of the roundabout we hold which includes data from the flyover. The data from the flyover is on the tab named “Great West Rd Chiswick NB”. This survey details the flows broken down into classes with counts in the morning peak, inter peak and the evening peak.
Do you have any plans to re-measure the volume of traffic using the flyover and if so when?
Finally, do you have any plans to replace the current flyover?
We have plans to improve Hogarth Roundabout as part of ourdrive to improve safety(which also includes Hogarth Flyover).The scheme, which is currently in the initial design phase, will aim to improve safety by addressing dangerous vehicle manoeuvres, make it easier and safer to walk and cycle across the roundabout, and introduce a lot more greenery.Additional data collection around volumes of traffic using the area will be carried out to inform any improvements.
Subject to funding being available, we hope to progress in the coming months and will be seeking views from the local community on current issues and future aspirations to feed into the scheme
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
