Tesco at Little Lever - Dossier - Appendix to Point No 10

Appendix to Point No 10

What the original Transport Assessment concluded

The Technical note in Appendix I of the Transport Assessment states the following conclusion:-

“11 Conclusion

11.1 From undertaking the three junction assessments of proposed signalised, double mini-roundabout and existing junction configuration, we conclude that only the configuration of the existing junction operates within capacity.

11.2 This is due to the fact that this junction operates at its maximum operational capacity when there is a free flow of traffic between Market Street and Church Street - as these are the two major traffic movements.

When implementing some form of control on the junction (i.e.signalised or double mini roundabout) it inhibits the free flow of traffic along these two arms. This results in congestion and subsequent queues along both Market Street and Church Street.

11.3 However it is understood from the local authority that there a number of safety issues at this junction relating to awkward vehicle manoeuvres and pedestrian movements. 

 Therefore if the existing configuration of the junction is to remain it is felt that this would not respond to the local authority’s safety concerns and would increase safety concerns due to the additional traffic.”

………………………………………………………………………………………

What Transport for Greater Manchester subsequently said:-

-----Original Message-----

From: Michael Reese [mailto:Michael.Reese@tfgm.com]

Sent: 23 December 2011 12:05

To: ajay@assuredplanning.co.uk

Cc: McCreesh, Aubrey

Subject: Little Lever - Tesco TA Review

Ajay,

Please find attached the review of the Transport Assessment for the proposed Tesco in Little Lever.

There are a number of issues but most notably is the use of PICADY4 for assessing the signalised

crossings at the Church Street/Market Street/Ainsworth Road/Lever Street junction.

We note that PICADY4 does not model signalised crossings but PICADY5 does and as such HFAS consider that the signalised crossings should be modelled with the best available software.

Also, as both traffic data and pedestrian data is in 15-minute intervals it would be best to model as such as this will more closely model the profile for the hour.

 HFAS has undertaken a preliminary run of the model using PICADY5 and 15 minute intervals and it indicates the junction may operate within capacity with signalised crossings on all arms.

………………………………………………………………………………………

What the designers of PICARDY said:-

Hello Paul,

Yes – This is well outside out our ‘call of duty’, but as the x-Product Manager of PICADY I still like to see PICADY used appropriately……………………………

2. The modelling of signalled crossings in PICADY is limited as it cannot model blocking back effects of the crossing – it only restrains the incoming traffic.  If traffic block the side roads this will not be taken account of at all.

 In reference to using the best software – my recommendation would be to use latest TRANSYT (TRANSYT 14).  This can model the crossing effects better.  It includes the PICADY model within it, so can model the side roads too.  Interaction between the two side roads could theoretically be taken account of too, but unfortunately this would require a calibration/validation process that is difficult if the junction is not yet build. Can only go on previous use experience for this, for which there may be none.

3. Finally wrt the question you ask: PICADY cannot model this situation as accurately as, say a standard T-junction, as it the product and the method described cannot take account of the interaction of the two side roads.  The original report that PICADY is based (see references in User Guide) did not include this layout.

 On the other hand, it is the best one can do with the product being used.  One might argue that if the side road traffic is very light and the junction results come out that each junction separately are well within capacity then there would not be a problem. 

An alternative would to set up a microscopic model, but they tend to need a lot of calibration and I question how much better they would be AND it cost a lot to do. 

Recommendation – use TRANSYT because of the presence of the signalled crossing – as if this causes gaps in the traffic on the main road for side road traffic to use - this is called “indirect traffic control” – something TRANSYT can model.

I hope you find this info useful.

Regards, Jim  Jim Binning BSc (Hons) MCIHT

Software Product Manager, Transportation. TRL

…………………………………………………………………………………………

From ‘Addendum to MVA Transport Assessment’ posted 29^th February 2012

3.30 Upon request and in liaison with TfGM/HFAS a re-assessment of the junction has been undertaken. This has been carried out in LINSIG which was recommended and approved for use by TfGM/HFAS.

…………………………………………………………………………………………………