Justification for road layout - Bath Road (A4)

The request was successful.

Dear Bristol City Council,

I wish to request information on the planning reasoning and justification for the layout at the crossroads of Bath Road, with Stockwood Road & Emery Road.

1) Why is this junction not a roundabout without traffic lights
2) why the Bath Road lanes split into two (heading East toward Keynsham) to then simply merge again around 500 yards later...

My main confusion lies in this splitting of the lane into two at the Bath Road crossroad junction, to then merge the two lanes of traffic later to no efficiency nor benefit to road users. As is the fact, drivers fundamentally struggle to merge when driving - this is evident.

I would like to know the justification around this and what the council plans to do as this area builds up considerable amounts of congestion at many peak times throughout the day.

https://www.google.co.uk/maps/@51.428863...

= My suggestion =

Run a trial to soothe the traffic heading East by using traffic cones to close off one of the two lanes before they split, thereby preventing two lanes of traffic queuing to merge yards later. This single queue of traffic has no further obstruction and will help reduce the congestion.

Yours faithfully,
James Wellington - Bristol resident

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No Reply @ Bristol, Bristol City Council

Dear James Wellington 
This is a courtesy email to let you know your Public Information
Request has been received on : 24/11/2017. 
Your unique reference number is "CRN00142645 ". Please keep this
number safe, as you may be required to provide it in the future. 
If you need to add further information concerning your case or
require an update about your response date, please email
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Customer Relations Team

"Customer Relations Team" <complaints.feedback@bristol.gov.uk>, Bristol City Council

You sent us a Freedom of Information request on 24/11/2017

Your request number is CRN00142645

We’ve looked at your request and you should receive a reply on or before 22/12/2017 13:15 This will be 20 working days since your original request.

The request

From: James Wellington [mailto:[FOI #448479 email]]
Sent: 24 November 2017 12:33
To: Freedom of Information
Subject: Freedom of Information request - Justification for road layout - Bath Road (A4)

Dear Bristol City Council,

I wish to request information on the planning reasoning and justification for the layout at the crossroads of Bath Road, with Stockwood Road & Emery Road.

1) Why is this junction not a roundabout without traffic lights
2) why the Bath Road lanes split into two (heading East toward Keynsham) to then simply merge again around 500 yards later...

My main confusion lies in this splitting of the lane into two at the Bath Road crossroad junction, to then merge the two lanes of traffic later to no efficiency nor benefit to road users. As is the fact, drivers fundamentally struggle to merge when driving - this is evident.

I would like to know the justification around this and what the council plans to do as this area builds up considerable amounts of congestion at many peak times throughout the day.

https://urldefense.proofpoint.com/v2/url...

= My suggestion =

Run a trial to soothe the traffic heading East by using traffic cones to close off one of the two lanes before they split, thereby preventing two lanes of traffic queuing to merge yards later. This single queue of traffic has no further obstruction and will help reduce the congestion.

Yours faithfully,
James Wellington - Bristol resident

Additional Information (if any)

If you don’t hear from us by this time please contact [Bristol City Council request email]
Contact details we have for you
James Wellington
 [FOI #448479 email]

 

Thanks

Bristol City Council

Max Thorley, Bristol City Council

Dear Mr Wellington,

 

The works at this site were carried out as part of the Greater Bristol Bus
Network project.  The outcome of the project was to improve bus
reliability and journey times along a series of arterial corridors around
the City.  The proposals also aimed to improve pedestrian accessibility
and enhancements to the public realm where possible.

 

As part of the preliminary design a range of options were considered,
these included:

·         Pedestrian accessibility and desire lines

·         Bus priority

·         Linking and progression along a signalised corridor

·         Traffic flow and congestion

·         Safety

·         Junction footprint

·         Construction

·         Cost

 

The junction lies between St Brendan’s college and Oasis Academy
Brislington and as such is the pedestrian route for a very large number of
students.  The junction modification included additional pedestrian
facilities, which is part of a wider strategy for ‘safer routes to
schools’.  Bristol’s local transport plan prioritises sustainable modes of
transport, such as walking and cycling.  With the traffic flows in the
area an equivalent crossing facility is not achievable by an un-signalised
roundabout.

 

Funding for the scheme was provided centrally as part of a drive to
improve public transport and linked to the local transport plan, it is
imperative that any changes to the junction did not have a negative
impact.  To help with the priority of Park and Ride buses, located next to
the junction, a bus gate was installed on Stockwood Road.  This allows the
buses to bypass the queue.  In addition buses are equipped with a
transponder, which requests the signals to be extended or demanded when a
late bus approaches.  This cannot be replicated if traffic signals aren’t
part of the design.

 

In urban areas traffic signals are usually linked to provide progression
along a route.  In Bristol we use a UTC (Urban traffic control) system,
which receives live data from sensors in the road to coordinate signalised
junctions.  This is a very effective way of maximising traffic flow along
a busy corridor.  However each road and junction has its capacity and
through this section of the A4 the traffic flows are higher than the
capacity of the network.  Once the traffic flows exceed the capacity of
the network queues start to form and congestion occurs.  Unfortunately
this is not easy to resolve and would require additional capacity by a
combination of more lanes, roads and/or bigger junctions, although an
increase in capacity often leads to an increase in the number of cars and
vehicles, which is not sustainable.  Alternatively measures such as gating
(queuing vehicles on the entry to a junction so that only what is
manageable on the network is allowed in) can be used, or to prioritise
sustainable modes of transports (walking, cycling, park and rides,
buses). 

 

With regard to safety in 2006 a national survey was carried out to the
reasons roundabouts were signalised.  The main reason was to provide queue
control (balancing the length of queues on all arms) at 80%.  The second
reason was safety, with a total of 72%.  Hengrove roundabout was
signalised nearly 10 years ago to reduce the number of rear end shunts.

 

For a roundabout to operate effectively particularly if there are high
numbers of right turning traffic it needs to be very large.  The inside
section of Hengrove Roundabout is approximately 120m, which is
approximately 3 or 4 times bigger than the Bath Road / Emery Road
junction, in all directions.  To build a roundabout of this size would
require significant land, which would need to be purchased at great
expense.  The budget for this scheme was a fraction of the cost required
to build a large roundabout.

 

The Bath Road / Emery Road junction is large, which accommodate additional
lanes at the signal stop lines.  This allows a reservoir to fill up while
the lights are on red, so that when a green light is shown more traffic
can proceed in the same length of time.  A rule of thumb is a car every 2
seconds, so 10 seconds of green for two lanes would equal 10 cars. 
However traffic does not always function like this.  Driver behaviour
varies and where there was a short merge on the exit, drivers would not
always use both lanes effectively, so perhaps only 6 or 7 cars got
through.  By increasing the merge to the Park and Ride signals it
increased the usage at the key point, Bath Road / Emery Road junction.
 The traffic signals on the outbound approach of the Park and Ride site
have a green light for a much longer period, so there is less of a
requirement to maximise two lanes of traffic through the green light.  

 

In the past we have had incidents or road works, which have caused one of
the outbound lanes to be closed.  When this happens there is a significant
impact on traffic flows leaving the City.  I am sorry that I cannot agree
to your request, however I hope my response provides some explanation to
the rationale behind the junction design.

 

Kind regards,

 

Max Thorley BSc (Hons) IEng FIHE

Traffic Signals & UTMC Manager

 

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