Response to HCC 003

BAA/3/Q revised

Response to HCC 003

This note has been prepared in response to the note HCC003 and relates to queries emerging from Ian Forshew’s evidence as requested by Counsel.

The delivery of the first version of HCC/1/G crossed with the delivery of the first version of BAA/3/Q.

This is a revised BAA/3/Q which elaborates on the earlier version and provides answers to specific points raised in HCC/1/G. These answers are referenced using the HCC/1/G paragraph numbers:

3. BAA had understood from HCC/1/A paragraph 4.10 that the improvements to the Little Hadham traffic signals had occurred in 2005. In any event, as explained earlier, the improvement had not taken place at the time that the traffic model was built and Halcrow had to make an assumption as to the signal set up and cycle time that would eventually be adopted. The recent test with the current set up and cycle time was undertaken to demonstrate why it is that the results referred to in Table D1 of HCC/1/D show a capacity in 2014 which is lower that that observed in 2003.

5. The highest recorded two-way flows are marginally under 1400 (Table D2 of HCC/1/A indicates an observed 2007 two-way flow of 1384 vehicles per hour) and the 2014 forecast two-way flow for the 35 mppa case with current traffic signal settings is 1537 (shown in Table G1 of HCC/1/G). This predicted increase in throughput is because there is presently some spare capacity insystem.

6 and 7. The BAA offer of a contribution toward the Little Hadham bypass was based on the incremental difference in traffic flows between the 25 mppa case and the 35 mppa enhanced +15% case both with a bypass in place (as shown in Annex A of BAA/3/E). For this reason, BAA do not consider that the issue of comparing the results from tests with different signal settings to be relevant. Nevertheless, we have responded to this issue in item 1 below.

8. It is correct that with the bypass the incremental difference between the 25 and 35 mppa cases is forecast to be 10 vehicles in the AM peak hour. Mr Forshew explained why it is that he considered this small change to be reasonable and pointed out that there was a decrease in AM peak hour traffic between the years 1999 and 2004in a period of rapid passenger growth and employee growth.

9 to 14. These paragraphs, like paragraphs 6 and 7, are all discussing the effect of the different signal settings and for the reasons stated above are not considered by BAA to be relevant but have, in any event, been addressed in item 1 below.

15. The new traffic forecasts, like the original forecasts, demonstrate that the impact of growth from 25 mppa to 35 mppa is extremely small (of the order of 10 vehicles per hour).

16. Growth to 35 mppa does not ‘trigger’ the need for a Little Hadham bypass. The relevant benefit has been calculated using the ‘with bypass’ forecasts of 25 mppa and 35 mppa +15% forecasts (see Tables A3 and A4 of BAA/3/E), which has an incremental growth in airport-related traffic of some 25 to 27 vehicles per hour.

1. Further details in the ‘Improved signalisation’ Traffic Forecasts produced by BAA week of 215 September.

The issue here focuses on the difference in flows as predicted by the SRTM traffic model for a 2014 AM peak hour between old and current signal timings at Little Hadham.

In BAA/3/F we provided the results for the 35 mppa 2014 AM peak hour test using the signal settings observed in September 2007 and in BAA/3/L we provided a simplified explanation to the question of how traffic would be predicted to re-route on the network. Figure 2 presented therein clearly showed where traffic had increased or decreased (in red and green) and where there had been no change. By looking at where the red and green diverge from a position where there is no colour, it is possible to see where the model is predicting that traffic will divert as a result of the increase in signal capacity. The figure presented was not intended to be comprehensive but it clearly showed how the model predicted that traffic would divert away from the B1004 and other east west routes onto the A120.

Understanding how the model predicts traffic re-routing is not simple and many factors are at play. These include:

PASSQ

The assignment process used in SRTM makes use of the PASSQ facility in SATURN (the ability to pass queued traffic from the previous hour in to the peak modelled hour). Use of the current signal timings result in an increased capacity at Little Hadham, which in turn reduces the queues in the ‘previous hour’, and thus reduces the PASSQ traffic that is passed. This will mean that the total number of trips in the tests of old and current signal settings will be slightly different.

Multiple User Class Assignment

The SRTM included 11 vehicle classes. Five of these are airport related; the other 6 are for non-airport traffic. They each have different generalised cost parameters, and thus in the assignment process, each could choose slightly different routes. As the delays at Little Hadham change between the old and current settings, the routes chosen by each of the 11 user classes could be affected.

Zone Definition

The SRTM has 452 zones, which included 27 zones for the airport, 36 zones for Bishop’s Stortford, and 24 zones for Harlow. The remaining 365 zones vary in size with greater definition close to the airport and less so further a field. Thus for an area such as Ware, a single zone represents the whole of the urban area, and the internal trips on the roads in Ware cannot be represented in the SRTM. As the proportion of airport related traffic in Ware is very low, this level of detail in the zone definition was, and still is, considered to be appropriate.

Model Noise

The SATURN assignment process does not provide a unique answer but relies on successive assignment/simulation loops to reach a position of ‘convergence’ in calculating network optimum routing solutions. This leads to small variations between successive loops, and between tests of different options. These variations, known as model noise, can contribute to small differences in flows. Model noise will play a very small part in the differences between the old and current signal model runs.

In Summary

Considering all of these factors, and most importantly, the purpose for which the SRTM was developed, the model can be seen to have provided a very credible response to the effect of changing the signal timings; there is nothing unusual in the results presented.

1. Traffic forecasts for Bishop’s Stortford

The issue regarding the 88 vehicles at the Tesco’s roundabout relates to the zone definition for this area. As was stated earlier, there are 36 zones in the SRTM model representing the urban area of Bishop’s Stortford. These zones match those used in HCC’s Bishop’s Stortford model.

One of these zones has been used to represent the housing areas to the west of the town (see Figure 1). This zone represents two distinct areas of housing that are not directly connected by a physical road. Figure 2 shows how this zone is connected to the road network, while Figure 3 shows the flow differences between the two tests.

Figure 3 reveals that the 88 trips are in fact modelled as entering the network on the B1004 and travelling into Bishop’s Stortford rather than using the bypass to the north of Bishop’s Stortford. In reality this demand would of course remain on the A120 and, as pointed out earlier, if the planned improvements to the A120/B1383 junction were incorporated into the model, then it would almost certainly reassign the demand back to the A120.

1. 24 hour or late night/early morning STEX services

The following statement has been taken from the Network Rail website.

STANSTED EXPRESS ANNOUNCES MORE SERVICES FOR PASSENGERS

Friday 5 October 2007 11:30

An extra 13 Stansted Express services a week will run from 9 December 2007 as improved night time working measures implemented by Network Rail allow more time to run passenger services.

The new extended timetable will help meet increased demand from business and leisure travellers, in particular at peak times (Fri-Mon), and will provide greater choice for people on late arriving or early departing planes to travel via rail using Stansted Express – the fastest way to and from the airport and central London.
A further nine additional earlier and later trains will also run on the West Anglia route, providing extra trains to stations including Bishops Stortford, Cambridge, Harlow Town and Sawbridgeworth as part of this initiative.

Derek Noakes, Business Director at Stansted Express said “We are delighted that, in partnership with Network Rail and One Railway, we have been able to introduce this added service for our customers. With the customer at heart, this new timetable furthers our commitment to provide a seamless link between London and onward destinations from Stansted Airport.”

Robin Gisby, Director of Operations & Customer Services at Network Rail said: “Increasing demand for rail means that passengers want trains to run from very early till very late, every day. We share this aspiration, but the challenge we face is how to make the very best of the few hours each night we have to undertake the necessary maintenance to keep trains running.

“By analysing how we plan our work on this stretch of track, we’ve identified where we can focus and be more efficient with our resources to get the same job done. This will enable more services to run and is a massive step towards our seven day railway vision and will make a real difference to people using Stansted Airport.”

A major communications and media plan to launch the new timetable to consumers, including advertising across the ‘One’ network, at key rail stations and at the airport, will start later this month.

Notes to Editors:

The new services will be as follows:

Last Trains from Stansted:

The 0030 Stansted Airport to Liverpool Street which previously ran each Monday, Friday, Saturday and Sunday mornings, now runs EVERY DAY.

An additional 0100 and 0130 Stansted Airport to Liverpool Street will run each Monday, Friday and Saturday morning.

First Trains from Liverpool Street:
The 0430 Liverpool Street to Stansted Airport which runs Monday, Friday, Saturday and Sunday mornings is retimed to start at 0410.

The 0455 Liverpool Street to Stansted Airport which runs every day is retimed to start at 0440.

On Sundays the 0525 and 0555 Liverpool Street to Stansted Airport departs at 0510 and 0540 respectively.

On Mondays there is an additional 0340 Liverpool Street to Stansted Airport service.

For More Information on Stansted Express and its services please contact the One press office on 020 7549 5964.

For more information contact:

Media Relations (London & South East)
t:020 7557 8359/9495
e:

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