Post-IMF Road Design Standards

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.

ardmacha

Good find ardmacha. Now we have some detail in place for exits on a new mid sized road.

Encouraged by the compliments, here is another one!

long slip road on Dutch 2+1

further discussion here

Amtmann

Retrofitting does not provide a solution for bad geometry and alignment either. It would be impossible to retrofit 98% of the N24 for instance. It's a non-runner in many cases.

blacktopper

Agreed Tremelo but we're not always talking about retro fitting the very old poor geometry roads in all cases. For example, the Wexford bypass on the proposed Rosslare-Oilgate scheme is built to modern standards it has excellent alignment and geometry site lines are superb. Same again on the other side of the Ferrycarriag bridge once you go round the bend that has to follow the coastline at that point its straight.

I'm still figuring out the OSI map tool but try these its all modern quality road:

Map 1
Map 2
Map 3
Map 4
Map 5
Map 6
Map 7

Few exits too as land adjacent was sterilized from building as it was designed to be extended.

blacktopper

How many other schemes will be replacing existing modern road constructions? The work on the mid sized option with retro-fit potential is a good project and could save millions/billions.

L1011

blacktopper wrote: »

2+1 in Germany too.

Generally unbarriered.


There is very little road in Ireland suitable to be retrofitted and in general, there are no plans for upgrades to those routes. Rosslare-Oilgate is possibly the only route where you can find enough examples.

The N20, N24, N5 to Mayo (within Mayo is a different story), N17 and similar could not be retrofitted for the vast majority of their length yet these are the roads with major plans for them.

blacktopper

I am encouraged that in your opinion the Rosslare-Oilgate present N11/N25 has adequate geometry and alignment to consider on-line upgrade, MYOB. But a little disappointed that no others could be also suitable. I will bow to your greater general knowledge on Irish road alignments but are you sure there are no others with similar relatively new roads?

Do you have any idea when the Wexford Bypass or any other sections of road in that scheme were built?

Amtmann

The N25 Kilmacthomas realignment could be retrofitted in my opinion and *possibly* a short section between New Ross and Waterford. Otherwise, I'm with MYOB. Most of the N-road network was built in the period from 1700-1850, is badly aligned with poor geometry, and is now littered with private accesses.

Other roads I know well:

N28: online upgrade seems impossible to me for 10 of its 13km
N25: mostly impossible to retrofit because of shocking geometry, private access and sinuous alignment
N24: absolutely impossible to retrofit
N71, N72, N73, N74: medieval-1700s design and impossible to retrofit
N30: new section that opened in 07 could be retrofitted, but a new build is required for the rest
N80: certainly un-upgradable from Portlaoise to Tullamore; I don't know about the rest of the route as I've never driven it
N21: I've never driven, but it seems at least some of the newer sections could be retrofitted
N22: Substantial sections require a new build (i.e. Macroom to Ballyvourney) because of AWFUL alignment, some sections have good alignment and geometry but are perhaps compromised by private accesses/villages, new hqdc section required for northern bypass of Cork City
N14: Never driven there, but seems awful
N50s and 60s are the pits and many need to be downgraded

Blacktopper: You should also think about proposing new routes that would allow for several national secondary roads to be retired.

Look at a map of the centre of the country for instance. An upgraded N80/N51 (i.e. a midlands corridor) and N4 (to type 2 dual carriageway standard) would allow the NRA to retire the N52, the N62 the N80 between Tullamore and Moate, the N81, much of the N5, the N63 and N61, while changing routes to make maximum use of the motorway/type 2 dc network. This is an indirect way of saving a lot of money (cutting maintenance costs on what SppongeBob calls the 'silly soup' of redundant national secondaries, while at the same time improving safety by funneling almost all traffic away from old deathtrap routes onto new alignments.

L1011

blacktopper wrote: »

Do you have any idea when the Wexford Bypass or any other sections of road in that scheme were built?

1988 comes to mind without doing any searching; my boyfriend hails from Wexford so I'd hope to be right on pain of death...

Tremelo wrote: »

The N25 Kilmacthomas realignment could be retrofitted in my opinion and *possibly* a short section between New Ross and Waterford. Otherwise, I'm with MYOB. Most of the N-road network was built in the period from 1700-1850, is badly aligned with poor geometry, and is now littered with private accesses.

I'd think the Youghal BP and maybe a few bits more of the N25 might be doable for retrofitting or overlay with very minimal land-take - 2M along an edge or so. Depends really on how long we'd want for a retrofit, a lot of the "runway" bits of the N25 are literally 1KM long overlays done when cash allowed in the past.

I would agree with your list of un-upgradeables above there, I've already given my limited list of roads that could be retrofitted, forgot the N4 though.

The N4 got an awful lot of attention due to Albert and other influences, there are a lot of 1990s S2/WS2 sections that are generally unimpinged or have a few farm accesses. But the NRAs plans for the N4 already include vast amounts of retrofit, the plan for the 2+2 from Dromod to the Carrick-on-Shannon BP includes only one deviation off the existing road, to blip around the hamlet of Aghamore. They've understood what can be done with the existing alignment, a lot of which predates the NRA in design terms. Of all the roads in the country I know the N4 and its development like the back of my hand, as its the road from "home" to home...

Realistically, for any nationwide retrofit plans, we're looking at late 1980s onwards WS2 work only - anything earlier has been completely compromised. Even the late 70s/early 80s N15 Ballintra Bypass has had commercial development open on to it for instance.

blacktopper

How many Km's are we considering suitable for retrofit then? Would it be economically feasible to develop a mid sized road option for these and also greenfield developments? I still think we need to develop this option otherwise few developments will occur. I still think "spreading the value" is the strategy we should at least be exploring with some degree of seriousness. The inner Midlands Corridor to the MIU's spokes suggested by Tremelo and Sponge Bob make sense but unless we can save money on construction and find a "do something else option" where possible such ideas may well remain thick blue lines on pdf's for decades. We need some openness about NRA future scenario's they probably have developed a number. Peer review will provide a consensus as to what is the most favoured scenario and highlight a number of valuable points during the process of discussion that could only be of benefit. At the moment we are playing other peoples tunes going on about Euro Routes. Other nations put S2's on parts of such routes they play their own tune for national advantage. The Dublin-Hub radials are in place. Linking the Hubs will help remove the ongoing Dublin-centric nature of the network. Opening faster economic routes between hubs. But treating all present schemes by 2+2 will render it a pipe dream. There is not the money. Other EU nations have mid sized roads so should we. Sure pool the best of what is out there but when something like a 2+1 doesn't work rather than shelve an approx. 10% saving on construction analyse what is at fault. Speed cameras at the closure of the 2 lane section back down to 1 lane; more sympathetic approaches to exits on left turns maybe even allowing hard shoulder stacking of traffic exiting on existing 2+1's would require little extra construction on a small section of the hard strip prior to an exit. What else can we consider or use? Sparse 2+1's as used in Sweden but with our safety considerations incorporated. There is a gap in the schedule of roads it was recognised by the NRA in the 2006 interim guidelines. Now we're broke we need to rediscover that gap but being older and more experienced in road building fill it better. Ideas on design welcome.

MYOB sorry to call you Mr. My apologises, it was presumptuous of me.

L1011

blacktopper wrote: »

How many Km's are we considering suitable for retrofit then?

200 or less nationwide. I'll admit to having relatively poor knowledge of the N2x in the south west, I've driven them all but generally only once or twice.

blacktopper wrote: »

Would it be economically feasible to develop a mid sized road option for these and also greenfield developments?

At this stage I think we're not going to agree on what is and what isn't a mid sized road option

blacktopper wrote: »

But treating all present schemes by 2+2 will render it a pipe dream. There is not the money.

We're not planning all present schemes as 2+2 though. The bulk of desperate-for-upgrade roads in Ireland are being planned to be replaced with Type 3 SC, those being the N5x and N6x series roads in general.

blacktopper wrote: »

There is a gap in the schedule of roads it was recognised by the NRA in the 2006 interim guidelines. Now we're broke we need to rediscover that gap but being older and more experienced in road building fill it better. Ideas on design welcome.
[/QUOTE

The NRA replaced 2+1 with 2+2 as their mid sized option.

The only option I can see thats "smaller" than 2+2 yet not just S2 is interpolating them. 2+1 just has too many problems, even with improvements for junctions and better relation of road shape to land shape; it shouldn't be considered for greenfield and I'd argue against it for retrofit either.

blacktopper wrote: »

MYOB sorry to call you Mr. My apologises, it was presumptuous of me.

Its not incorrect though...