Follow-on from 1942-1920: Thank you very much for your response of 19 September. It is certainly informative, but doesn't go quite into the level of detail I was seeking. I am seeking further detail as follows: 1. The answer you give states the no U-turn signs were erected in October 2014, yet Google images from May 2015 clearly show that neither of two no U-turn signs had been fixed to the signals by then, can you explain this? https://www.google.com/maps/@51.5857104,-0.2308789,3a,15y,358.37h,91.88t/data=!3m7!1e1!3m5!1s4YryIVOhfDtqJexgCPN6NQ!2e0!5s20150501T000000!7i13312!8i6656 2. The magnitude of the changes to saturation clearly shows they result mostly from other changes than the ones I raised in my question. What modelling, if any, was done to specifically compare options: (i) Make all the changes implemented by May 2015 versus (ii) Make most of the changes implemented by May 2015, BUT do not permit flow G during stage 3 (the 'extended left turn' from the Burroughs), and maintain the U-turn from northbound A41 to southbound A41? With or without keeping the vehicle movements in the sequence they follow in the pre-2015 Method of Control, so that flow G remains unbroken between stages. and if so, how do the results compare? 3. In the model, what is the assumed ratio of traffic in flow G to that in flow F? 4. When modelling the full May 2015 implemented option, what assumptions were made re the behaviour of the displaced U-turn traffic, which would have U-turned from northbound to southbound but must now take alternative route, and quantities? E.g. mean of 1.9 vehicles displaced per traffic signal cycle at busy times, 30% of those displaced might enter the Burroughs and U-turn there then proceed to southbound A41, 20% enter the Burroughs and detour via Wykeham Road, 20% enter Station Road and U-turn there, 10% change to making right turn from northbound A41 at Central Circus, being locally destined, 20% divert down Rundell or Neeld Crescent then east along Vivian Avenue, being from local start point. 5. How were the consequences of these displaced movements presented/summarised? E.g. were they reflected in terms of increased junction saturation on the Burroughs and Station Road resulting from those U-turning there, and junction saturation displaced from this junction to Central Circus A41 northbound resulting from those displaced to turning right there? 6. Were the increased journey times and emissions from the mostly longer displaced movements also quantified and presented as a consequence? Kind regards,

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Dear Mr Levy

TfL Ref: 2013-1920

Thank you for your request received by us on 24 September 2019 asking for information about traffic modelling following your previous request for information (reference: 1142-1920).

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. You asked for the following:

1. The answer you give states the no U-turn signs were erected in October 2014, yet Google images from May 2015 clearly show that neither of two no U-turn signs had been fixed to the signals by then, can you explain this? https://www.google.com/maps/@51.5857104,-0.2308789,3a,15y,358.37h,91.88t/data=!3m7!1e1!3m5!1s4YryIVOhfDtqJexgCPN6NQ!2e0!5s20150501T000000!7i13312!8i6656

We apologise for the incorrect information regarding the date that the banned u-turn signs were erected. We will answer your questions as best as we can from the information that is available to us. The paperwork we initially reviewed suggested it was October 2014, however, further investigations indicate that these signs were added when the new traffic signal timings were implemented on street, which was on 30 May 2015.

2. The magnitude of the changes to saturation clearly shows they result mostly from other changes than the ones I raised in my question. What modelling, if any, was done to specifically compare options:

(i) Make all the changes implemented by May 2015

versus

(ii) Make most of the changes implemented by May 2015, BUT do not permit flow G during stage 3 (the 'extended left turn' from the Burroughs), and maintain the U-turn from northbound A41 to southbound A41? With or without keeping the vehicle movements in the sequence they follow in the pre-2015 Method of Control, so that flow G remains unbroken between stages.

and if so, how do the results compare?

Modelling was carried out that tested the ‘original’ Method of Control (MoC – this is a term we use to describe the traffic signal stages and phases which operate at a junction without Phase G in what became Stage Three. We have referred to them as MoC A (Original), and MoC B (Present-day), and we have compiled the results from the models attached.
 
The attached data shows the degree of saturation in percentage terms. Saturation is a measure of demand versus capacity used in junction traffic modelling to ensure that timings are balanced effectively according to demand from all users.

3. In the model, what is the assumed ratio of traffic in flow G to that in flow F?

In the morning peak hour, Phase F has more than four times the number of PCU (Passenger Car Units) as Phase G. In the evening peak hour, Phase F has more than 3 times the number of PCU’s as Phase G. For reference, a car has a PCU value of 1; a bus or HGV has a value of around 2 PCU’s. 3

4. When modelling the full May 2015 implemented option, what assumptions were made re the behaviour of the displaced U-turn traffic, which would have U-turned from northbound to southbound but must now take alternative route, and quantities? E.g. mean of 1.9 vehicles displaced per traffic signal cycle at busy times, 30% of those displaced might enter the Burroughs and U-turn there then proceed to southbound A41, 20% enter the Burroughs and detour via Wykeham Road, 20% enter Station Road and U-turn there, 10% change to making right turn from northbound A41 at Central Circus, being locally destined, 20% divert down Rundell or Neeld Crescent then east along Vivian Avenue, being from local start point.

The u-turn movement was not modelled in the pre-2014 base scenario. Therefore no assumptions were made as to where these vehicles would be displaced to, or the impacts of any displacement. There is no documented reason as to why this movement was not modelled, so our assumption, based on extensive experience is that the numbers of vehicles making this turn were very low.

5. How were the consequences of these displaced movements presented/summarised? E.g. were they reflected in terms of increased junction saturation on the Burroughs and Station Road resulting from those U-turning there, and junction saturation displaced from this junction to Central Circus A41 northbound resulting from those displaced to turning right there?

6. Were the increased journey times and emissions from the mostly longer displaced movements also quantified and presented as a consequence?

As the u-turn was not included in the original 2014 base model, the displace movement’s consequences were not summarised.

Journey time and emission changes as a result of the U-turn ban were not modelled. Such a modelling assessment would not be undertaken for this type of small scheme. The purpose of this change was to remove instances where vehicles were blocking back over junctions on the A41, in addition to improving journey times on the A41.

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

Jasmine Howard
FOI Case Officer
Information Governance
Transport For London

 

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