Post-IMF Road Design Standards

miles deas

Hi,
This thread is aimed at posting ideas and examples for a new mid-sized road option. Its all about one possible "Do Something Else Option". The debate about if one is needed could start here but lets get some options first. I'll put some background in first if that helps:



So a capacity AADT of anywhere between 14,00 and 18,000 say.

here's what we have already:





Here's the land take for off-line construction:


Any idea is worth a punt on-line, off-line, construction materials or methods. You name it, if its an idea post it. Can we aim for constructive criticism there are bound to be posters with limited experience of road design and pro's. So help those who need it get the most from their ideas critique not criticism.

miles deas

If accidents tend to happen at the end of the 2 lane section of a 2+1 because people squeeze in a cheeky overtake why not have a speed camera or dummy camera toward the end of as many such sections as possible. Could the RSA work with the NRA to publicize any such dangers intermittently.

runway16

I've been following the last thread with interest Sir.

You did indeed have a point all along, but sadly you got mired with a few misunderstandings concerning road types, compounded by some dodgy information from others.

Now that those have been resolved, you have a very worthwhile argument, and it is indeed a debate worth having on how we keep some investment going in these more frugal times.

My own view - we still need the M20, Cork Northern Ring Road, The atlantic corridor as at least a 2+2, the N24 as a 2+2, and a the remaining small sections of motorway or type 1 DC that the NRA have planned and seem to be proceeding.

I'd also argue that either the N4 or M3 corridors need to be developed as at least 2+2 to serve the North west to ensure it has equivalent access.

Beyond that, we need to examine the sort of road type for the few remaining national primaries that will never justify a motorway, and indeed for the busier national secondaries.

miles deas

Good point it doesn't stop it just changes there will always be areas of highest priority things may not change there. Its the ones in between that need thinking out of the box. If you have any ideas please share your thoughts. If your interested Sponge Bob mentioned. Sparse 2+1's. The accident rates on rural dual carriageway is about 3 x10 to the power 8 per km while 2+1 is 4 to the same power per Km. If some ideas come on how to address this the the sparse 2+1 might fly. From the other thread widening 40% of an existing road instead of 100% sounds worth investigation in these times.

Thanks, signing off now, night.

L1011

Any form of 2+1 means that one direction has no overtaking opportunities *at all* for a period of time. Seeing as we have slow moving traffic using national routes, this is the main reason that 2+1 is a failed road type and was removed from the standards list for new builds.

If you'd actually drive a bit, you'd see that 2+1 is a poor road type, and you'd also see that there is little difference between it and 2+2 in land take and carriageway width (due to 2+1 needing a larger hard strip and refuge areas on the single side, as well as much larger deceleration areas for junctions. 2+2 is a mid sized road.

Sections of 2+2 would not have this problem but would still suffer from the bunching problems familiar to anyone who ever drove the A1 to Belfast more than a couple of years ago - this at that time had patchy DC between the border and Hillsborough

dubhthach

miles deas wrote: »

If accidents tend to happen at the end of the 2 lane section of a 2+1 because people squeeze in a cheeky overtake why not have a speed camera or dummy camera toward the end of as many such sections as possible. Could the RSA work with the NRA to publicize any such dangers intermittently.

This is indeed a problem, I know for example where the M11 narrows to single carriageway (Arklow gap) that there is always a mad dash up the overtake lane to try and squeeze in before the merge.

In general I do think we need more work from the RSA for example on 3 lane motorway with "middle lane hoggers". I wouldn't be surprised that alot of problems are due to the fact that there is no mandatory driver training in Ireland. In lot of European countries you have to do 20hours certified lessons before you can do the driving test.

Sponge Bob

We should look at interspersing 2+2 and S2 on certain corridors, eg the N5 and N21 and N22. Reliable overtakling opportunities every N KM should be provided by 2+2

As regards driver behaviour

1. The end of a 2+2 should be merge only ( no overtaking) with enforcement.
2. "Move Over" laws together with laybys should be considered on National Primary S2 sections ....with enforcement.

corktina

congrats on the new thread. Now that you have "gone native", can we expect a change of name to "kilometre deas"?:D

miles deas

Kilometres Deas it is then. Regarding platooning of cars (all bunched up behind a front slower vehicle) on single carriageway sections of a 2+2-S2 alternating stretch. What would people consider acceptable is there any safety or economic data.?

Remeber 4 lanes may offer the best driver experience but economics is important too. I know your belief that 2+2 is the ultimate mid-sized road Mr MYOB, a few years ago it would be hard to argue with you. Now maybe the best value lies in accepting a degree less of service for a cheaper option. I'm not saying necessarily 2+1 I believe its only 10% cheaper, on average. But maybe Sponge Bob's 2+2-S2 alternating road or sparse 2+1 which has mainly SSC with intermittant stretches of new 2nd lane alternating.

Mr MYOB you do a lot of driving in your line of work have you seen any other examples of road lay-outs in your travels for this target area?

I'll put up a UK slide that shows opening year AADT ranges for some roads. I'm not pushing necessarily for WS2, cos I'm not. But more the traffic range I think is worth a focus upon:



regarding dubhthach's comment on mandatory driver training, I think your right. That sort of long sighted investment lasts a driver a lifetime with an annual return through that time. I bet if you ask the ESTC they'll give you a wealth of data of financial returns 100's of percent greater than the initial investment. But it will be hard to champion at the moment when we're 7th out of the EU 27 for safety. Still if the economics is there it would be hard to dismiss.

Where else are the safety problems on 2+1's? Run with it for a second Mr MYOB just want to work this thing through.

miles deas

Just had a thought on Sponge's 2+2-S2 concept. If we had more automated traffic counters we could target the S2 to the less trafficked sections on a route. It would enable a more consistent LOS (level of Service - a measure of driver experience sudden braking or platooning of traffic in little slow moving clusters etc.). Even when the road switches to cheaper S2 single carriageway.

I'll keep putting the explanations in to keep this accessible to all. Sorry the experts amongst us. You never know where a good idea might come from so keep it accessible if you have the time.

Sponge Bob

miles deas wrote: »

Just had a thought on Sponge's 2+2-S2 concept. If we had more automated traffic counters we could target the S2 to the less trafficked sections on a route.

Exactly, instead of intermittently measuring traffic for a single scheme we do a "whole of route" analysis. In the example of the N5 there are rural sections eg east of Charlestown and west of Ballaghadereen that do not carry as much traffic as NEAR and AROUND those towns. The 2+2 stretches should generally bypass a town around where the heavier traffic is. One could nearly go for Type 2 SC on those stretches were it built offline but I am minded to build Type 1 SC de minimis on a route like the N5.

As regards S2 stretches and platooning I would point out that much platooning is caused by crap drivers and crap drivers will not pull onto hard shoulders. Therefore we need laybys at predictable intervals on those S2 stretches together with a move over law.

The move over law should generally state that where a car is not constantly driving at a MINIMUM 80% of the permissible speed limit on the stretch AND where more than 4 cars are held up by that front car THEN the driver of the front car MUST pull into the next drivethru layby and let those cars past after which they may pull out and proceed. In practice that means 80kph on a 100kph road.

That means we need proper laybys with good merges but only for 200m out of every 5km. It also means we need not build hard shoulders that nobody uses...especially those who should use them the most.

This all makes the user experience more predictable and therefore much safer but does not require WS2 type roads and their associated land take or an overabundance of 2+2. If you do find yourself bunched you know that the gobdaw in front will have to pull over within 5km.

It would be possible to implement a move over law by retrofitting laybys to existing WS2 and even S2 as well. It should certainly be piloted on one of the more adequate ones. However in most cases we have no option but to build a new offline road because the existing one cannot be upgraded properly.

miles deas

Fair point Sponge. I get frustrated by slow drivers that won't pull over. Do you know of any international examples of similar laws to 1) provide a president and 2) a possible template. Its not a necessity we can have the good ideas first. The sort of cautious drivers that do this are just the sort that would religiously follow the law with minimal enforcement needs. I'm no lawyer but airtight drafting of this law would possibly be unnecessary. Its very presence on the books would probably have a significant effect. I bet the RSA has some cool term for this phenomenon and some research to boot that it causes frustration in other drivers and dangerous overtaking and accidents. Getting that would add weight to the proposition.

Amtmann

I think you need to establish a list of routes scheduled for upgrades that you are happy to have as type 2 dual carriageway for the full length of the road, and then outline your compromise solution for other specific routes.

miles deas

Tremelo, I'm not so sure it might look presumptuous of me. I don't have knowledge of the whole network like some of you guys do. What I could do is lay that open for all to make comment on and then offer to summarize at the end of each week with a table with 1 column showing the route another 2 columns showing positive and negative posts for 2+2 upgrade for each route and another 2 columns for positive and negative comments on a smaller on-line development. What do you think?

miles deas

I have enough knowledge of one route to post on that. But I don't want it to become too route specific a thread. But it would add relevance and more specific useful contributions especialy if Sponge Bobs 2+2-S2 alternating route option flies. The problem is I have my true name on this and I don't want to trash the thread by seeming biased to one route or a solution. Maybe I need an alias.

Tech3

Which road do you have in mind miles deas? I think we will allow the discussion of any route once it stays on this thread.

Sponge Bob

Well we only want to see a single route as an example. I picked the N5 because I know it. People do understand the difference between an EG and Outright Advocacy around here.

You may change your username if a mod nicely asks an admin, PM a suggested new one " Blacktopper " is available for ya

miles deas

N11/N25 Rosslare-Oilgate. I think it can be argued an on line option with upgrades as proposed by Sponge Bob could fly.

dubhthach

miles deas wrote: »

I have enough knowledge of one route to post on that. But I don't want it to become too route specific a thread. But it would add relevance and more specific useful contributions especialy if Sponge Bobs 2+2-S2 alternating route option flies. The problem is I have my true name on this and I don't want to trash the thread by seeming biased to one route or a solution. Maybe I need an alias.

I wouldn't be too worried about been seen as biased when it comes to route selection. In general we all tend to have our own little "biases" -- for example as a Galway man I want the Outer bypass etc.

The important thing in general is to put forward your argument to "the floor". There could be features of that route which are applicable/similiar to other ones.

miles deas

Can a mod. change my name please to "the Scarletpumpinickle" or something equally foolish then?

Amtmann

miles deas wrote: »

The problem is I have my true name on this and I don't want to trash the thread by seeming biased to one route or a solution. Maybe I need an alias.

miles deas wrote: »

Can a mod. change my name please to "the Scarletpumpinickle" or something equally foolish then?

We all know some routes better than others. I'm clueless about most of the N50s and 80s for instance, and I don't know much about the N12-N16 either.

If you aren't happy with having your real name appearing here, maybe you'd like to register a new Boards.ie account with another email address and choose something more anonymous, and then post under that. Your posts thusfar would remain as written by Miles Deas, but all new posts would be under the new name you pick. That would be no problem in this case, seen as how you are being very open about everything. Up to you entirely! None of us have the ability to change your username though, unless you actually subscribe to Boards.ie for a small fee, in which case the admins will do it for you. Otherwise, registering a new account would be the best solution for you.

But I do think it would be good to have a few specific routes named and discussed for your design ideas, just so people can better visualise the solution as well as spot potential problems, practical difficulties, etc.

Sponge Bob

miles deas wrote: »

N11/N25 Rosslare-Oilgate. I think it can be argued an on line option with upgrades as proposed by Sponge Bob could fly.

Dunno about that one The Only Online possibility I see is that the Wexford Bypass could be made 2+2 with Offline S2 south and Offline 2+2 North to Enniscorthy.

The road further north has too many entrances for it to be online upgradeable...in my opinion and from memory.

But I await the case...agog! Try using OSI maps to illustrate a point rather than Google which has dreadful road maps. Here is one spot with different overlays selected according to the number at the end. Practise a tad.

http://maps.osi.ie/publicviewer/#V1,700586,628607,6,1
http://maps.osi.ie/publicviewer/#V1,700586,628607,6,2
http://maps.osi.ie/publicviewer/#V1,700586,628607,6,3
http://maps.osi.ie/publicviewer/#V1,700586,628607,6,4
http://maps.osi.ie/publicviewer/#V1,700586,628607,6,5
http://maps.osi.ie/publicviewer/#V1,700586,628607,6,6

Convert OSI to Long and Lat ( or vice versa) using

http://www.fieldenmaps.info/cconv/cconv_ie.html

Simply enter OSI x and y example above, ie 700586 628607 into Irish Transverse Mercator field and press convert

Yahoo maps are vastly superior for Irish Roads as they NOW exist.

eg

http://maps.yahoo.com/#mvt=m&lat=55.431618&lon=-7.241814&zoom=14

blacktopper

Good afternoon gentlemen. I would like to contribute to the lads comments regarding Rosslare-Oilgate's proposed scheme. I wonder if there are sufficient grounds to advocate 2+2 throughout. Such as the port itself, is it a sufficient driver. I would like to show the traffic growth between 2007-2010 right at the port NRA automated counter N25-1 on the proposed route and surrounding counters as my first piece of evidence showing the fall in traffic around the proposed route:



Traffic, particularly at the port is shrinking at an ever increasing rate. What conclusions do you draw?

blacktopper

Just got the above Sponge will have a go.

Sponge Bob

You may presume we all read this too

blacktopper

I presume some of you may even of had a hand in writing it.

Sponge Bob

We would also know about this and personally I would generally consider Jan and Dec 2010 to be weather related anomalies.

blacktopper

If we ignore the falling traffic but follow present NRA predicted growth as per appendix 6 we show traffic growth as per below:



We never get to the max capacity threshold of S2. This is what got me interested 6 months ago. What would your initial thoughts be if you were me?

munchkin_utd

Again to re-iterate, on long cross country journeys, a mere or 3 individual slow motorist, holing up entire swathes of traffic, can add hours to your journey.

i suggested an idea before that is cheap and maybe suited to the more frugal post IMF times. It occured to me after many many frustrating kilometres en route from North of Cavan to the far side of Cork City.

On the N3 between Cavan Town and the Kells ByPass, I was behind a reasonably quick truck doing mostly 80, which at the same time slowed to 60kph for the crack of it every so often. The road is good quality, but still hard to overtake as its also busy in the other direction. So on a quiet day you would tip along at 90/ 100kmh no bother with the exception of Virginia Town.

Anyhow, we both slowed at the roundabout at the Cavan/ Meath border, but afterwards where theres 2 lanes, I blasted by him within seconds (as trucks and pensioners driving clapped out fiats have VERY slow acceleration)

The same happened to me on the 2+1 heading out of Letterkenny. The 2 lanes AFTER the roundabout afforded me the chance to very quickly steam by slower traffic that I was behind since the town.

To compare, the 1km overtaking sections on the Mallow 2+1 are not long enough, as you are moving along at 80 or 90, so actually have very little time to overtake.

The essence and elegance of my idea is that by overtaking at a slower speed, you get the advantage of a better acceleration of car vs truck (/15year old fiat) and you are both travelling slower, so you have longer to overtake so more people can overtake.
AND its a localised solution, as opposed to the long stretches that otherwise would be built.

And going back to the Roslare-Oilgate section.
Heres heading away from the roundabout at the southernmost section of the Wexford bypass, where a car is stuck behind a horse trailer, which on all probability they have been behind for kilometres.
http://maps.google.de/maps?f=q&source=s_q&hl=en&geocode=FYCfHQMdfoye_yk9iHeEJxpoSDFAHjKXqccACg%3BFbXgHwMd2mCc_ynPaK1uwgNoSDHwlTGXqccACg&q=Rosslare+to+Oilgate&aq=&sll=51.151786,10.415039&sspn=15.571663,47.768555&ie=UTF8&ll=52.303231,-6.461377&spn=0,0.046649&z=15&saddr=Rosslare&daddr=Oilgate&layer=c&cbll=52.30322,-6.461389&panoid=R4e_v6VXZe1hFTSKQgHaxg&cbp=12,242.59,,0,14.19
You could say that the horse trailer pull in for the car behind.
With my solution, the car would be past the horse trailer already after leaving the roundabout!!

Another advantage is that the cars are NOT going at full tilt coming into/ exiting a roundabout. With the lower speeds the solution is cheaper than a normal 2+1 as you could even get away without a central barrier (making the solution in the case of existing roundabouts like the roslare bypass no more than the cost of re-painting lines !!)

Amtmann

And again, please DO NOT make AADT the sole determinant in your analyses. You must also consider the current road's alignment AND geometry, as well as the amount of private accesses along it. Private accesses include houses, farmyards, pubs and field gates. Then you must consider junctions, where regional and local roads meet the main road. AADT may be a lot lower than the maximum capacity, but when you factor in all of the above, you see that the road's viability and utility as a transport corridor is greatly diminished.

blacktopper

Fair point Tremelo, but do those junctions affect say collisions on the road? after all that's one of the important factors regarding junctions and say 15% of the economic benefits. If I trawl the older work I found this:



I get your point, but where would the BCR be if traffic is down and accidents were low to start with. Quid pro quo.

blacktopper

munchkin_utd, regarding the overtaking opportunity maximisation after roundabouts. If treated right and mindful of safety why not. I like all this astute observations once someone puts it down in writing you can immediately identify with it.

The find on google maps street view is a good one.:D

Amtmann

Private accesses and junctions affect many things (including safety), particularly where they coincide with an undulation in the road's geometry, or a bend in its alignment, or both. They severely restrict overtaking opportunities and contribute to bunching. They also mix local, slow-moving traffic with national, long-distance traffic. They can restrict sightlines and mean that the speed limit of 100km/h can often not be reached, even when drivers are not stuck behind a lorry or tractor. Where private accesses occur on bends, the NRA cannot remove said bends because it would mean expensive CPO-ing for minimum improvement (not enough bang for the buck). These factors all drastically affect the level of service* offered by the road, and mean that even though the AADT is technically rather low, functionally the road is at capacity or above it for all intents and purposes.

I presume you all know what 'level of service' refers to. If not, these relate to the utility of roads as transport corridors, pegged to economic goals. For more, see the Road Needs Study (1998), available in part here.

blacktopper

Yes I understand LOS. I posted an explanation on the other thread. I think the application is made a bit arbitrarily. Once a section of road comes under scrutiny then it ain't difficult to use such arguments. When just up the road there might be several more severe examples that have been ignored. That sort of thing might diminish the argument a bit.

marmurr1916

Tremelo wrote: »

And again, please DO NOT make AADT the sole determinant in your analyses. You must also consider the current road's alignment AND geometry, as well as the amount of private accesses along it. Private accesses include houses, farmyards, pubs and field gates. Then you must consider junctions, where regional and local roads meet the main road. AADT may be a lot lower than the maximum capacity, but when you factor in all of the above, you see that the road's viability and utility as a transport corridor is greatly diminished.

This is a very important point. The ability to progress along a route at a decent average speed, and a high degree of certainty about journey times, should be equally important considerations when road designs are being discussed.

Even a route with relatively low AADT can have low average journey speed, with uncertain journey times because of the factors outlined above.

Optimal road design not only takes into account AADT figures but also allows for adequate progression along the route and certainty about journey times.

blacktopper

Off to work now. But this is interesting will post when home tomorrow.

Thanks

L1011

miles deas wrote: »

Where else are the safety problems on 2+1's? Run with it for a second Mr MYOB just want to work this thing through.

*Scramble overtaking as a 2 section ends and the inherent dangers thereof
*High speed rear-ends as someone turns off from a 1 section. There is often a slightly wider hard strip but not enough to remove anything bigger than a small car from the driving lane.
*Sideswipes as people attempt to let someone pass on a +1 by pulling in to the hard strip while moving, ala WS2 (this would work with two Micras passing, but nothing else).

Basically, 2+1's are lethal with Irish driving and traffic levels. They are used to provide passing places on low traffic rural roads in Scandinavia. Here we use climbing/crawler lanes to similar affect but far cheaper.

There is another safety risk of using passing lanes on flat surfaces as you again reach the possibility of a 250km/h headon, because generally these lanes are marked as usable by both directions with a priority for one. 2+1s would be safer than that but then introduce their own problems.



Sponge Bob's suggestion of interspersed S2/2+2 has legs. The problem is that this isn't generally possible as a retrofit except to areas where the existing road is already offline. The ribbon development along any decent quality older road in Ireland means that they are dotted with private accesses, crossing traffic, etc.

As soon as you go offline, the cost benefits realistically vanish, and its quite likely that five years down the track you'll need to 'bore out' the S2 sections to 2+2 due to traffic rises.

There are many mostly upgraded routes where this could be done, though. Taking the N25, a 2+2 bypass of Castlemartyr, a 2+2 bypass of Dungarvan, 2+2 of New Ross and sporadic 2-3km stretches of 2+2 overlaid on new build WS2 such as the Youghal and Kilmacthomas bypasses could easily be sufficient for the next few decades. But there's not many routes with as much % of already decent S2. N4, N5 through Mayo alone, parts of the N15 maybe.

L1011

munchkin_utd wrote: »

The same happened to me on the 2+1 heading out of Letterkenny. The 2 lanes AFTER the roundabout afforded me the chance to very quickly steam by slower traffic that I was behind since the town.

That's a full 1980s quality "standard DC" (similar to the Midleton BP, Nass-Newbridge, N4 Downs or other old DC) not a 2+1... i

ardmacha

I don't think 2+1 is ideal except for retrofit. However

They are used to provide passing places on low traffic rural roads in Scandinavia.

What traffic levels are these used at, exactly?

Scramble overtaking as a 2 section ends and the inherent dangers thereof

Camera here, and strict enforcement, would do wonders.

*High speed rear-ends as someone turns off from a 1 section.

It should be possible to build a short section of declaration lane here. I agree that these are very much needed.

L1011

ardmacha wrote: »

What traffic levels are these used at, exactly?

Dunno. I've driven one and it felt similar in numbers to the sections of the N9 that had 6-7,000. Googling suggests some are as low as 4,000.

ardmacha wrote: »

Camera here, and strict enforcement, would do wonders.

No automated way for a camera to determine "dangerous overtaking", and it is possible to be dangerous below the speed limit.

ardmacha wrote: »

It should be possible to build a short section of declaration lane here. I agree that these are very much needed.

Could be done but they've made a hames of out where they've tried to so far - narrow, short 'pockets' more than lanes, all they really do is let you in enough to stop a trailing car smacking your arse. Even on the totally virgin new build that has grade seperated junctions (Castleblayney) this is a major fault. As is having 2 sections going *downhill*. Twice!

ardmacha

No automated way for a camera to determine "dangerous overtaking", and it is possible to be dangerous below the speed limit.

Hatch an area a bit back from the merge, ticket any car that enters the hatched area.
I don;t think it has to totally automated, just identify suspicious behaviour that can be reviewed by a person.

Even on the totally virgin new build that has grade seperated junctions (Castleblayney) this is a major fault. As is having 2 sections going *downhill*. Twice!

I couldn't agree more!

L1011

ardmacha wrote: »

Hatch an area a bit back from the merge, ticket any car that enters the hatched area.
I don;t think it has to totally automated, just identify suspicious behaviour that can be reviewed by a person.

Workload would be huge but that could work. Would be lots of "they wouldn't let me merge back in, waaaaaaah" defences though.

ardmacha wrote: »

I couldn't agree more!

If it wasn't for your username I'd suspect you were my brother. But he'd be in C&T more

dubhthach

MYOB wrote: »

Workload would be huge but that could work. Would be lots of "they wouldn't let me merge back in, waaaaaaah" defences though.

Given the general standard of driving in Ireland you would probably win the case with that argument.

MYOB wrote: »

If it wasn't for your username I'd suspect you were my brother. But he'd be in C&T more

Thar be dragons!

runway16

dubhthach wrote: »

This is indeed a problem, I know for example where the M11 narrows to single carriageway (Arklow gap) that there is always a mad dash up the overtake lane to try and squeeze in before the merge.

In general I do think we need more work from the RSA for example on 3 lane motorway with "middle lane hoggers". I wouldn't be surprised that alot of problems are due to the fact that there is no mandatory driver training in Ireland. In lot of European countries you have to do 20hours certified lessons before you can do the driving test.

The NRA and RSA know about the "middle lane hogging" problem. They were told, and there response was that a new TV motorway driving ad campaign would start last november. It did, but was the same old campaign about driving on two lane motorways.

These guys just dont listen - they dont even seem to drive these roads themselves. The only thing the RSA really give a **** about is speed.

blacktopper

Regarding ardmacha's useful comments. He asks for max. AADT Swedish 2+1 information, its 20,000 veh./day, see below:



notice we have lower max. capacity, once again pushing to more costly alternatives:



He also asked about treatment of exits to prevent rear ending queuing, exiting traffic. I thought this might help.HA UK using existing hard shoulder (obviously standard of construction of hard shoulder would need to be considered):



see, link.

These ideas coupled with the camera idea at the end of the 2 section are all good adding to the existing 1m hard strip to create an exit lane is good.

L1011

They may have 20k as their max capacity but the majority of their 2+1 roads are nowhere close in current usage. Remember their 2+1 network was done by stringing barriers down existing wide rural roads, not high capacity routes.

I'd suspect they leave significantly more headway than we do.

dubhthach

Regarding Sweden I'd be curious about the population densities through the area's that they mostly run 2+1. I know from some photo's I've seen that some of the area's with 2+1 look as desolate as parts of Connemara.

ardmacha

High speed rear-ends as someone turns off from a 1 section.

Compare a Swedish road junction (taken at random from Google) with the right angled nature of the N2 / R183 junction at Castleblayney.

I know from some photo's I've seen that some of the area's with 2+1 look as desolate as parts of Connemara.

Its says on Wikipedia that there is some 2+1 in Denmark, which may be more similar ti Ireland, I wonder where they are?

blacktopper

2+1 in Germany too.

blacktopper

I think each nation has it's own driving characteristics and therefore accident risks. We need therefore to adapt imported road layouts to reflect this. for example from a communication from Swedish Roads Authority. Accidents around exits aren't a problem so they don't take measures:



I've just looked at ardmacha Google Street View pic.'s, go look. They say they don't have accidents around exits in Sweden so they don't treat. the reason they don't have exit accidents is because they have a partial exit lane already in place. Good find ardmacha. Now we have some detail in place for exits on a new mid sized road.

SeanW

A problem with most of our current single carriageways - including WS2 roads, is that they have frequent private accesses and junctions with minor roads, which, in their capacity as a single carriageway, long distance or not, doesn't bother me too much.

Case in point the N4 between Palmerstown (Co. Dublin) and Edgeworthstown (Co. Longford) where, due to a variety of Urban dual carriageway, Motorway, Reduced Dual Carriageway (RD2, abolished early 2000s) Standard Dual carriageway (Mullingar BP) and finally Single Carriageway from Mullingar to the Edgeworthstown relief road ... you can "cruise" between Palmerstown and Edgeworthstown only stopping to pay the M4 toll.

Needless to say the RD2 type dual carriageway is gone, so the 2+2s commonly used roundabouts instead, and roundabouts are used, a little too much I think, on new road schemes.

However, I digress. If you propose to "retrofit" an older single carriageway with some kind of divided DC, be it 2+1 or 2+2 or anything else, you have to provide for the myriad of private houses etc that will no longer be able to safely exit/enter their premises to/from both directions. They would either have to cross the road at an SC section making a U-turn (not very safe), or have a roundabout provided for them (pain in the bollix for long distance drivers).

So here would be my plan, after seeing the main corridors upgraded to a high quality DC/Motorway type (by this I mean M20 Cork-Limerick, N4 Mullingar to Longford etc):
1) Bring back the RD2 standard for low AADT routes - where traffic using the junctions would be limited - allowing linked roads access to the DC while ensuring long distance traffic gets to "cruise" through with priority. Similar to the current Downs dual carriageway in Westmeath.
2) For existing wide roads for which there is no real money available, simply repaint the roads to have no hard shoulders but instead have overtaking lanes, in as much as they are wide enough. It would not be as safe as a 2+2 or even RD2 or 2+1, but it would limit the potential of slowpokes to cause tailbacks. As an example I would say do this on the N5, the N4 while it waits for upgrade, and any wide sections on the national secondary roads.