SW Exeter P&R – where will that traffic come from?

At the recent public consultation event on the proposed site, there was a curious display – one that on the face of it should undermine the whole concept of the siting of a park & ride scheme anywhere to the west of the city.

It was this one:

APHINGTON P&R: Origin of traffic on Alphington Road
APHINGTON P&R: Origin of traffic on Alphington Road

Let’s take a closer look at the pie-chart – taken at face value it is suggesting that 60% of the traffic currently using the Alphington Road corridor – and thereby potential users of the new P&R site by the Ide Interchange.

But the chart also raises a number of questions – questions that a statistician would be likely to ask.

Percentages in such diagrams hide a number of sins – where is the total number of vehicles surveyed?

Was it 100? Was it 1000? Or 10,000? and remember that 10,000 would only be about the number of vehicles using Alphington Road in a day.

So was the survey taken over an hour? A day? Or a week?

And how was the data collected?

Was it the result of roadside interviews? Or analysis of data collected by some sort of automatic numberplate recognition?

Earlier data collection has been well documented.

In August 2009, Parsons Brinckerhoff prepared  the Alphington Junction Part and Ride Transport Assessment.

The report contained a table of a survey was conducted by Parsons Brinckerhoff at Matford P&R in June 2003. Users of the P&R were asked the origin of their journey and the results are summarised in the table below.

Origin of Matford users
Origin of Matford users [2003]

In 2004, roadside interviews [RSI] were undertaken at several sites, detailed in the map below.

2004 Roadside Interview Sites
2004 Roadside Interview Sites

These RSI identified the total market for potential Park & Ride users was identified using the origin and destination locations of cars.

This data was used in the Devon County Council’s Alphington Interchange Park and Ride Transport Report published in March 2011.

Origin of traffic from 2004 Road Side Interviews
Origin of traffic from 2004 Road Side Interviews

So is that new pie-chart an outlier? I believe so, and I think the problem stems from WHEN the data was collected.

I’ve already suggested there was a problem presenting undated data, so f my guess is correct, the figures stem from 2014 when Junction 29 was being remodelled and unusual traffic movements would mean drivers were seeking new and unusual ways to get into the city centre.

Whatever the reason for the errors, DCC must stop using this chart if they want to convince people that a P&R scheme is necessary on this site!

UPDATE [24 July 2015]
I have heard from DCC over their definition of East and West.

It appears that those coming from the East aren’t following a star or anything, but from A30 East or from Teignbridge and Plymouth direction. Which in turn means come from the (south) west, via A38 not the east and M5

The data was collected from from Roadside Interviews (RSIs) which are the most accurate surveying method for being able to establish where drivers are starting and ending their journey and therefore what the potential market for Park and Ride may be.

Due to the significant disruption and cost associated with organising these surveys, RSIs are rarely undertaken to support Transport Assessments for planning applications (so in this respect, having the data is a luxury).

There is no intention to undertake any further surveys of this type but I am told  that the Transport Assessment will use Automatic Traffic Count 2014 data.

Generally, the Department for Transport considers traffic data collected within 5 years of the submitted analysis to be suitably representative of conditions

Update from @DevonCC on #SWExeter Park & Ride

I’ve had a update from Devon County Council to summarise the current position, which I post unedited – I trust this is helpful…

The County Council maintains that there is a strong case for a Park and Ride site (with opportunities to Park and Cycle, Park and CarShare) at the interchange of the A30/A377; however, we took a decision to pause and re-evaluate the alternative options as we may at some point need to demonstrate why no other alternative site is suitable. We have always been clear that the site must be within the vicinity of this junction because it will attract people from both the A30 and A38 directions, therefore our assessment included sites within 500m of the junction. Outside of this range and traffic is expected to find it too remote and there would also be substantially increased revenue costs associated with running bus services to the facility.

I’ve set out below some of our reasons for proceeding with pre-application discussions on the basis of the ’round field’ site…

Environmental
There are a number of challenges in delivering a Park and Ride facility on the Oaklands site, which is part of the Alphin Brook Conservation Area and Valley Park.

Whilst we believe that there are opportunities to sensitively design the site to minimise landscape/visual impacts and enhance the park with additional planting and new improved routes, it remains a sensitive issue amongst the local community and key stakeholders, including English Heritage.

The Round Field site is part of an Area of Great Landscape Value; however, is an isolated field located between the A30, which runs directly alongside one edge of the field and the road that leads to Ide (it is largely out of view from this approach). Although a raised site, we believe that with appropriate planting, the impacts from long distance views can be minimised.

Accessibility
Given the busy nature of Alphington Road, in order to serve the Oaklands site there would need to be significant junction works to introduce signals and also address the level changes between Alphington Road and the site itself. Furthermore, at some places, a 4 lane-wide carriageway would be needed to provide for an inbound bus lane, an inbound all-traffic lane, an outbound traffic lane and an outbound right turn lane into the P&R. This would require loss of the screen of trees running along Alphington Road and would be costly in engineering terms.

The round field site, by comparison, is served off a less busy road and could be accessed by a simple roundabout junction. A junction in this location may also have the benefit of slowing speeds for traffic exiting the A30 and heading towards Ide.

In the morning peaks, traffic exiting the A30 (and turning right towards the city) can queue in lane 2 on the slip road.

Similarly, traffic exiting the A30 (from Okehampton) queues in lane 1 on the slip road.

The Park and Ride traffic would be able to use the comparatively empty lanes towards Ide to bypass the queues and gain easy access to the facility.

There would still be plans to create an inbound bus lane but this would make Alphington Road only 3 lanes wide and could retain the screen of trees along its length, therefore minimising the environmental impacts.

There is scope to improve cycle routes from the round field site towards the city centre as there is a route under the A30 adjacent to it.

There is also potential to improve walking and cycling routes to local communities, offering opportunities for residents to interchange with a frequent and direct bus service to the city centre.

Size
Our most recent assessment concluded that a 600-space P&R facility would be sufficient based on predicted demand; however, the ’round field’ site was previously rejected on the basis of a 900-space car park. Our assessment suggests approximately 600 spaces could be accommodated at the round field site and therefore should not be discounted as an option for being ‘too small’.

Cost
Both the County Council and District Councils have less funding directly available to them and there are significant demands on Community Infrastructure Levy, therefore it is important that we find a solution that delivers best value for money.

There were significant costs associated with the Oaklands Site, namely the need to raise the site by 1 metre in order to achieve satisfactory drainage and the highway works described above under ‘Accessibility’.

Although a full cost assessment has not been carried out for the ’round field’ site, the fewer environmental constraints and ‘simplified’ highway works would suggest it could be delivered at a reduced cost to the Oaklands site.

We are planning to host a public consultation at West Exe School between 4pm and 8pm on 21st July, where there will of course be opportunities to ask officers questions about the proposals.