Thoughts on the A303

[Chris5156]

Such a scheme might be practical IF it took a very smoothly curving route across the north of Salisbury - perhaps no further south than Old Sarum - and IF there was also a plan to upgrade the A36 significantly, so that the A303 and A36 could share the section up the Wylye valley (one road is cheaper than two) and the A36 could bypass Salisbury using just a new section of road to the east.

There's no commitment to do anything with the A36, though, and as a standalone scheme this makes much less sense.

If you could route it on a straightish line from Porton on the A338 to Stretton on the A36 you'd have a reasonable compromise but I expect that will be too close to a number of other sensitive locations and the idea will be for a road further south.

[J6onM27]

There was a version I saw similar to this on this forum, but cannot seem to find it anymore. I would think this could be a great D2 with full GSJ solution.

[JammyDodge]

Random thought i just had.
As most will know, the Bullington Cross interchange with the A34/A303 is dreadful in terms of safety and efficiency. Traffic queues on the A303(east) heading into the junction at busy times. Merging is deadly, due to the world's shortest slip road (metaphorically) and speed is impossible to build up to with the sharp curves off of the roundabouts and the single T-Junction.

My suggestion is for an improvement:
Build a bypass for the A34 and A303 around the junction. With the A34 routed west and the A303 routed north of the existing junction. This idea is somewhat like what the A34/M4-J13 Junction (https://goo.gl/maps/ASxMcbJrdgvbnDHV8)
I think originally, the A34 went around the roundabout under the M4 until the Newbury bypass was constructed.

My idea would be to build 2 new main alignments of the trunk roads and leave bullington cross with little modification. This would allow for merging onto the existing carriageways to be unhindered by allowing lanes between slip roads to decrease, thus negating the problem with the short slip roads and difference in speeds and traffic flow. My only modification to the current bullington cross junction would be to add another roundabout in to replace the T-Junction connecting to the A303(west).

I believe that this would be the most cost effective way of modifying the junction, as well as improving safety and merging issues.

Please leave me some feedback

[Herned]

Random thought i just had.
As most will know, the Bullington Cross interchange with the A34/A303 is dreadful in terms of safety and efficiency. Traffic queues on the A303(east) heading into the junction at busy times. Merging is deadly, due to the world's shortest slip road (metaphorically) and speed is impossible to build up to with the sharp curves off of the roundabouts and the single T-Junction.

Please leave me some feedback

Firstly, not sure it's even an issue.

Secondly, if the length of the slip roads is a problem, lengthen them...

Thirdly, I assume Winchester-Andover is the biggest turning movement, and Nb-Wb already has a free flow slip, then if need be add another loop all the way round to do Eb-Sb

There is no need to replace both roads. I say this as a resident of the southwest who has used that section of the A303 up to daily for 25+ years. Obviously data and anecdote are not the same thing, so if there is data showing the junction is worse than my experience it would be good to see it

[JammyDodge]

Random thought i just had.
As most will know, the Bullington Cross interchange with the A34/A303 is dreadful in terms of safety and efficiency. Traffic queues on the A303(east) heading into the junction at busy times. Merging is deadly, due to the world's shortest slip road (metaphorically) and speed is impossible to build up to with the sharp curves off of the roundabouts and the single T-Junction.

Please leave me some feedback

Firstly, not sure it's even an issue.

Secondly, if the length of the slip roads is a problem, lengthen them...

Thirdly, I assume Winchester-Andover is the biggest turning movement, and Nb-Wb already has a free flow slip, then if need be add another loop all the way round to do Eb-Sb

There is no need to replace both roads. I say this as a resident of the southwest who has used that section of the A303 up to daily for 25+ years. Obviously data and anecdote are not the same thing, so if there is data showing the junction is worse than my experience it would be good to see it

The Biggest issues come from the heavy traffic heading Westbound on the A303, Then having heavy traffic join from the A34 Northbound struggles to merge. I have only been driving 3 months, however i have used this junction to go to and from Winchester from Andover when learning and to visit friends. The heavier the traffic, the worse the problems are. Overall, it is a good junction, however there just is not enough room to enlarge the slip roads, three bridges and the A30 to Sutton Scotney. The current A34 threads through a gap between homes.

This is is a good way to improve the future capacity of the junction, especially if the A303 is fully duelled to the A30/M5 (maybe before I'm dead) and the A34/M3-J9 junction is made free flowing, which is likely to increase traffic (as these things do overtime).

While it is just about fine for the minute, this junction will eventually need a solution.

Edit: Found some sources to support and upgrade due to capacity
https://bit.ly/2ZrR4uf - M3 Junction 9 Improvement Scheme Supporting Documents

• Section 1.2.6 - Says that HGV traffic on the M3 and A34 will have doubled between 2005 and 2020, with an overall growth of 33%

• Section 3.3.1 - The table here shows a traffic survey undertaken by SkyHigh in June 2015. It shows that the Annual Average Weekday traffic going onto the A34 Northbound is 28722 (13.8% HGV), Southbound is 27081 (13.7%) and that Average Hourly Flow between 10:00-16:00 is 2032 Northbound and 1880 Southbound

https://bit.ly/2ZpN7qG - Solent to the Midlands Route

• P9, 'A safe and serviceable network', "Further north between Winchester and Newbury, there are issues around the slip roads with accidents involving
  HGVs. The slip roads at Bullington Cross for the A34"

• P9, 'Supporting economic growth', "On the A34
  corridor between Southampton and Newbury, there are
  high traffic flows to junction 13 of the M4, reflecting its
  important strategic role in linking economic growth in the
  north and south"

• P12, Map, "A34/A303
  Northbound slip is a problem for HGVs "

• P23, 'A34 Winchester to Newbury', "Further congestion is anticipated in the longer term due to increased traffic volumes on the route, particularly at
  the junction between the A303 and A34"

• P23, 'A34 Winchester to Newbury', "There is an incident cluster site for traffic merging on the A34 northbound from Bullington Cross"

[Chris5156]

My idea would be to build 2 new main alignments of the trunk roads and leave bullington cross with little modification. This would allow for merging onto the existing carriageways to be unhindered by allowing lanes between slip roads to decrease, thus negating the problem with the short slip roads and difference in speeds and traffic flow. My only modification to the current bullington cross junction would be to add another roundabout in to replace the T-Junction connecting to the A303(west).

Welcome to SABRE!

Realigning both trunk roads around the outside of the junction, while leaving the junction alone, is a very expensive way to get anything done, and wouldn't do much to increase capacity or safety at the junction itself because it would still be there in its present form. For much less money you could leave the roads where they are and make significant changes to the layout of the junction itself. You could, for example, build just two more bridges and a couple of new sliproads, and convert the whole thing into a three-level stacked roundabout junction with much improved geometry and sliproad merges to modern standards.

[Johnathan404]

Firstly, not sure it's even an issue.

Secondly, if the length of the slip roads is a problem, lengthen them...

Thirdly, I assume Winchester-Andover is the biggest turning movement, and Nb-Wb already has a free flow slip, then if need be add another loop all the way round to do Eb-Sb

Without a doubt the junction is seriously unfit for purpose. All of the slip roads are too short, especially given the sharp bends and the steep climb on the A34. A lengthy extension is required, especially for the A34 northbound. Extending the A34 southbound onslip, where traffic regularly comes to a stop, would most likely require the A30 to be acquired and re-aligned. That is not a cheap project, before you even consider replacing the two bridges to allow for proper segregation of the deceleration lanes, which I appreciate is not likely but would be of benefit.

The roundabouts are not only far too small for such a major link, but the appalling vertical profile of the northern roundabout encourages poor driving. The only reason there aren't more HGV rollovers is that it at least looks as bad as it is. Not exactly 'mile a minute'.

The T-junction usually has a short queue which is never a good sign, but at least a shunt on the downhill is less dangerous than somebody overshooting the give way line.

The collision stats are in the public domain and are exactly where you would expect them to be: clustered around the T-junction, the northern roundabout and the A34 southbound onslip. Surprisingly there is very little collision history where the link road dives under the A34.

Having said that I agree a complete realignment would be excessive. It is difficult to think of a practical way to untangle the mess especially given that the turning manoeuvres are still relatively low, just too high for an S2 T-junction.

[Herned]

....Section 3.3.1 - The table here shows a traffic survey undertaken by SkyHigh in June 2015. It shows that the Annual Average Weekday traffic going onto the A34 Northbound is 28722 (13.8% HGV), Southbound is 27081 (13.7%) and that Average Hourly Flow between 10:00-16:00 is 2032 Northbound and 1880 Southbound[/list]
...
Northbound slip is a problem for HGVs ....There is an incident cluster site for traffic merging on the A34 northbound from Bullington Cross

That's interesting, I would have thought the HGV proportion would be even higher than those numbers

Fair enough then, either extend the sliproad, or add a third lane up the hill (ideally all the way to the M40!), or even add an entirely new free flow slip road from the A303 to the A34N.

For E-S traffic a new slip road could be fitted in along the course of the old railway. Which would save demolishing homes

[jackal]

Just needs two new bridges to be rearranged as a full freeflow partially-unrolled cloverleaf. A third bridge would be needed for a new A30 GSJ to the south.

[JammyDodge]

My idea would be to build 2 new main alignments of the trunk roads and leave bullington cross with little modification. This would allow for merging onto the existing carriageways to be unhindered by allowing lanes between slip roads to decrease, thus negating the problem with the short slip roads and difference in speeds and traffic flow. My only modification to the current bullington cross junction would be to add another roundabout in to replace the T-Junction connecting to the A303(west).

Welcome to SABRE!

Realigning both trunk roads around the outside of the junction, while leaving the junction alone, is a very expensive way to get anything done, and wouldn't do much to increase capacity or safety at the junction itself because it would still be there in its present form. For much less money you could leave the roads where they are and make significant changes to the layout of the junction itself. You could, for example, build just two more bridges and a couple of new sliproads, and convert the whole thing into a three-level stacked roundabout junction with much improved geometry and sliproad merges to modern standards.

My idea for the junction would be to reduce lanes after the slips from the A34(N)-A303(W), between the other slip on the A34(N), as well as the slip off of the A34(S), A303(W) and A303(E). This would allow for safer merging in this idea, with longer acceleration lanes, merges and allowing the A34(N)-A303(W) traffic have its own lane when using the sliproad. This would be done using paint, signs and extending some curbs

I understand that this would be expensive, however capacity of the junction would increase as the A34 and A303 traffic passing through the junction would be removed, thus only traffic changing roads will pass through the junction.

Another thing is that the realignment would pave the way for a full replacement for the junction in the future, around the crossing of the new alignments. This would help solve one of the big problems with infrastructure in general in this country, where cost is everything, and that the future isn't planned for with such thinking.

[JammyDodge]

Just needs two new bridges to be rearranged as a full freeflow partially-unrolled cloverleaf. A third bridge would be needed for a new A30 GSJ to the south.



a34 a303 big - Copy.jpg

This is good, and i thought the same, however the disruption caused would be great. This junction also does not provide for the scrapyard in the middle of the junction, the farm access and the A30, which I believe is the A34 diversion route

[Peter350]

Just needs two new bridges to be rearranged as a full freeflow partially-unrolled cloverleaf. A third bridge would be needed for a new A30 GSJ to the south.



a34 a303 big - Copy.jpg

You wouldn’t need the A303 Westbound - A34 Southbound slips and vice versa as traffic wishing to use that movement would take the M3.

[JammyDodge]

Just needs two new bridges to be rearranged as a full freeflow partially-unrolled cloverleaf. A third bridge would be needed for a new A30 GSJ to the south.



a34 a303 big - Copy.jpg

You wouldn’t need the A303 Westbound - A34 Southbound slips and vice versa as traffic wishing to use that movement would take the M3.

You would still need these slips as the M3 is a little while away, and as such would be providing for local traffic as well as if the M3(N) is shut, it would be a possible diversion route

[Peter350]

Just needs two new bridges to be rearranged as a full freeflow partially-unrolled cloverleaf. A third bridge would be needed for a new A30 GSJ to the south.



a34 a303 big - Copy.jpg

You wouldn’t need the A303 Westbound - A34 Southbound slips and vice versa as traffic wishing to use that movement would take the M3.

You would still need these slips as the M3 is a little while away, and as such would be providing for local traffic as well as if the M3(N) is shut, it would be a possible diversion route

I did a similar drawing over a year ago which utilises the old A30 for the A34 - A303(E) turning movements.

download/file.php?id=12782&mode=view

[Glom]

Just needs two new bridges to be rearranged as a full freeflow partially-unrolled cloverleaf. A third bridge would be needed for a new A30 GSJ to the south.

a34 a303 big - Copy.jpg

Sort of nice except the biggest problems are the merges from the cloverleaves and this doesn't change that.

[jackal]

Just needs two new bridges to be rearranged as a full freeflow partially-unrolled cloverleaf. A third bridge would be needed for a new A30 GSJ to the south.

a34 a303 big - Copy.jpg

Sort of nice except the biggest problems are the merges from the cloverleaves and this doesn't change that.

Two of them are removed entirely, the third is realigned with a larger radius and merge.

[Richardf]

While you would lose a couple of free flow links a basic 3 level roundabout junction would be the simplest solution, and could still include freeflow filter lanes for the busiest movements.

Trying to provide a fully freeflow junction here is too optimistic, I think what we have now is the best it could be in that regard. If you could take the A30 connection out of the equation then it's possible but I don't think removing the A30 is a feasible option.

Consider the history of the junction. The present layout was designed to give access to the Bullington Cross Inn, while making the junction as freeflow as possible. If the pub hadn't been there a much better layout would have been used. The fact that the pub no longer exists doesn't really change things.

[Johnathan404]

Consider the history of the junction. The present layout was designed to give access to the Bullington Cross Inn, while making the junction as freeflow as possible. If the pub hadn't been there a much better layout would have been used. The fact that the pub no longer exists doesn't really change things.

Is there any evidence for that or is it just an urban myth? I ask because it sounds an awful lot like "the M62 was routed around a stubborn farmer".

The publicity at the time suggested the main priority was keeping the A34 on a gentle gradient, which would help explain the layout. There was also a lot of talk about keeping costs down. I'd suggest the fact the chosen design could easily factor in the pub was a mere coincidence.

[jackal]

I've never really understood the obsession with three-level roundabouts. There is no net advantage compared to the basic structural form that's already there. Some movements would be better, some worse, but the basic situation of two grade separated mainlines with low turning capacity between them would remain. Seems a pretty pointless way of spending a couple of hundred million (as indeed was the related proposal for M2 J5).

If the complaint is with length of slips then just lengthen the slips. If more raw capacity is needed put in more freeflow left turns, still at a tiny fraction of the cost and disruption. If yet more capacity is needed (which I doubt tbh) then a stackabout wouldn't work either and a freeflow rebuild is required such as that I posted above. This would of course be disruptive and expensive but at least it gives you a step change in functionality, which is not the case with a stackabout sidegrade.

[KeithW]

Consider the history of the junction. The present layout was designed to give access to the Bullington Cross Inn, while making the junction as freeflow as possible. If the pub hadn't been there a much better layout would have been used. The fact that the pub no longer exists doesn't really change things.

Is there any evidence for that or is it just an urban myth? I ask because it sounds an awful lot like "the M62 was routed around a stubborn farmer".

The publicity at the time suggested the main priority was keeping the A34 on a gentle gradient, which would help explain the layout. There was also a lot of talk about keeping costs down. I'd suggest the fact the chosen design could easily factor in the pub was a mere coincidence.

There is in fact a wiki entry that covers this and a very old thread discussing it. The consensus was that it was built the way its to keep the A34 gradient down and minimise the land take and cost.
viewtopic.php?f=1&t=11211
https://www.sabre-roads.org.uk/wiki/ind ... gton_Cross

It certainly was not built for the benefit of the Inn which lost trade, was closed in 2007 before being demolished and the site has become scrap yard.