At some point in mid-2015 a U-turn prohibition was introduced on right turn traffic from the northbound A41 at The Burroughs, to forbid such traffic U-turning to the southbound A41. Apparently at the same time, the green signal phase for left turn traffic from The Burroughs to the A41 was extended to start earlier. The two changes appeared to be connected. I am seeking (i) the dates of the two changes; (ii) all the information that was factored into the decision to prohibit this particular U-turn. In particular I wish to know if any modelling was carried out and if so, what data was involved and a summary of the model.

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Our ref: FOI-1142-1920

Thank you for your request received on 9 July 2019 asking for information about changes to traffic signalling.

Your request has been considered in accordance with the requirements of the Environmental Information Regulations and our Information Access Policy. I can confirm we do hold the information you requested. You asked:

Dates and justification for prohibiting U-turns from northbound A41 to southbound at The Burroughs

At some point in mid-2015 a U-turn prohibition was introduced on right turn traffic from the northbound A41 at The Burroughs, to forbid such traffic U-turning to the southbound A41. Apparently at the same time, the green signal phase for left turn traffic from The Burroughs to the A41 was extended to start earlier. The two changes appeared to be connected. I am seeking (i) the dates of the two changes; (ii) all the information that was factored into the decision to prohibit this particular U-turn. In particular I wish to know if any modelling was carried out and if so, what data was involved and a summary of the model.

Changes to the traffic signals at this junction were implemented in both October 2014 and May 2015. These changes were delivered as part of a scheme to increase junction capacity. This included extending the right turn lane on the southbound approach of A41 Watford Way and the addition of new pedestrian facilities across Station Road.  This resulted in the left turn out of Station Road being signalised. Furthermore, the operation of the signals at the Burroughs was altered so the left turn could receive a green signal at the same time as the northbound right turn from the A41. These changes were implemented in May 2015.

To facilitate running The Burroughs left turn movement in this new traffic stage, a traffic order was required to ban the U-turn movement whilst travelling northbound on the A41. This was necessary due to potential for conflict between u-turning traffic and left turning vehicles exiting The Burroughs. The traffic order was signed in September 2014 (https://www.thegazette.co.uk/notice/2201400) with signs banning the U-turn erected at the junction in October 2014. Traffic modelling was carried out to assess the capacity impacts of this scheme, the results of which are included below. These were used to justify the scheme being implemented.  The traffic modelling results indicate changes in Degree of Saturation (DOS), which is the way we quantify how a junction can cope in clearing queuing traffic through each phase of signals. For this junction the results show that DOS improves for all movements in the morning peak period, and on the heaviest movement (A41 Watford Way) in both directions in the evening peak period. There is an increase in DOS for The Burroughs and Station Road, but the proposed DOS is still under 100%, which is our preference when we make changes of this nature. 

Methods of Control before May 2015:

Current Method of Control, implemented May 2015:

If this is not the information you are looking for, please do not hesitate to contact me.

Please see the attached information sheet for details of your right to appeal.

Yours sincerely,

Jasmine Howard

FOI Case Officer

General Counsel

Transport for London

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