[Article] Dual-carriageway speed limit increased to 120kph

unkel · 28-05-2006 1:39am

So 120km/h on the N2 and
100km/h on the M50 southern stretch?

Is that because of all those terms used such as 'D2AP' and 'D2M' you guys mention? What are these? Are these to do with compensating multi-millionaire farmers whose land these new roads are built on? Why?

murphaph · 28-05-2006 9:07am

unkel wrote:

So 120km/h on the N2 and
100km/h on the M50 southern stretch?

Is that because of all those terms used such as 'D2AP' and 'D2M' you guys mention? What are these?

No, it's because the M50 southern cross and SE motorway traverse the foothills of the Dublin mountains. The sightlines/braking distances are poorer than the N2 and the crosswinds may be a factor too.

D2AP is Dual 2 lane All Purpose, ie, nop motorway style restrictions on the vehicles or drivrs that may use it. (it could be a high quality dual carriageway or a standard one with median crossings, generally all D2AP being built in Ireland is high quality, ie, fully grade separated with no median crossings, just like a motorway)

D2M is Dual 2 lane Motorway, physically the same as HQD2AP*

(the N2 amongst others is D3AP for some of its length of course).

*not a recognised acronym that one, made that up!

unkel wrote:

Are these to do with compensating multi-millionaire farmers whose land these new roads are built on? Why?

In part, almost certainly!

corktina · 28-05-2006 9:50am

my guess on whether a road is desginated M or N has to do with the viability of the remaining infrastructure after a Mway is built (for non-motorway traffic....)
ie if the new road replaces the old with no alternative available for non-mway traffic, then it should be an N wheras if the new road is in addition to the old system then it can be an M

murphaph · 28-05-2006 9:59am

corktina wrote:

my guess on whether a road is desginated M or N has to do with the viability of the remaining infrastructure after a Mway is built (for non-motorway traffic....)
ie if the new road replaces the old with no alternative available for non-mway traffic, then it should be an N wheras if the new road is in addition to the old system then it can be an M

But this simply isn't the case for most of what's planned. The entirety of the N6 from Kinnegad to Athlone will be offline new build (as will almost all new interurban dual carriageway) which leaves the old road intact. It's got a lot more to do with placating/compensating landowners than any technical reason.

Victor · 29-05-2006 6:49pm

murphaph wrote:

No, it's because the M50 southern cross and SE motorway traverse the foothills of the Dublin mountains. The sightlines/braking distances are poorer than the N2 and the crosswinds may be a factor too.

Apparently the M50 thing was down to noise, nothing else.

jlang · 29-05-2006 9:17pm

Victor wrote:

Apparently the M50 thing was down to noise, nothing else.

Noise originally may have been the overriding factor in the preliminary design, but the design speed was 100kph and that was what the curves were designed for. Doesn't really matter because the upgrade will definitely be 100 - design speed and posted limit.

The design speed on some of the "free-flow" ramps on the upgraded interchanges will be as low as 30kph - still better than 0 when stopped at a traffic light but it's awful slow. Also, some of the ramps will only really be one vehicle wide which is fine until a truck breaks down and has to be towed away or there's a shunt. At least on the wide roundabouts, that only causes a delay, not a complete blockage.

unkel · 30-05-2006 12:27am

Thanks murphaph for explaining that. Not that it makes much sense to me

jlang wrote:

Noise originally may have been the overriding factor in the preliminary design, but the design speed was 100kph and that was what the curves were designed for

Crosswinds and curves and line of sight, etc. do not seem to be a problem @120km/h, surely?

As for noise, what one does is build a noise-reducing wall in relevant areas to eliminate the problem. Was this never considered?

jlang wrote:

The design speed on some of the "free-flow" ramps on the upgraded interchanges will be as low as 30kph - still better than 0 when stopped at a traffic light but it's awful slow

That's very slow. Ideally they should be designed to maximum motorway speed, but if there's not enough space, you'd expect at least 80km/h. Then again it's much better than traffic lights

jlang wrote:

the upgrade will definitely be 100 - design speed and posted limit

After the upgrade, is the whole of the M50 going to be 100 or just the southern cross part where the limit is currently 100?

murphaph · 30-05-2006 9:33am

unkel wrote:

Thanks murphaph for explaining that. Not that it makes much sense to me

You're welcome Unkel!
Roads are classified thus;
S1 (single carriageway, single lane, think country boreen with grass in he middle!)
S2 (single carriageway, 2 lanes)
WS2 (wide single carriageway, 2 lanes-a lot of the N road network is like this, hard shoulders generally visible)
D2/3/4* (Dual carriageway, 2, 3 or 4 lanes each side etc. Note there is no accepted way of implying a dual carriageway with say 3 lanes on one side and 2 on the other, weird but there you go. The * can be AP for all purpose or M for motorway).
Oh, and not forgetting 2+1 whch we'll be seeing a lot more of.

unkel wrote:

After the upgrade, is the whole of the M50 going to be 100 or just the southern cross part where the limit is currently 100?

100 everywhere. The lanes are being reduced from 3.75m to 3.5m in width along almost the entire M50.

unkel · 30-05-2006 9:53am

Thanks again, Philip. I understand now

murphaph wrote:

Oh, and not forgetting 2+1 whch we'll be seeing a lot more of

Yeah they seem to refer to it as the "Swedish system", but it is quite common in most continental countries, notably France where it is used as a climbing lane (2 lanes up, 1 lane down). A good replacement for WS2 if D2 is not quite necessary

murphaph · 30-05-2006 11:35am

unkel wrote:

Yeah they seem to refer to it as the "Swedish system", but it is quite common in most continental countries, notably France where it is used as a climbing lane (2 lanes up, 1 lane down). A good replacement for WS2 if D2 is not quite necessary

The jury is still out on 2+1 in many quarters. If drivers all behaved in a responsible manner then S3 would be better than 2+1. We never had S3 in Ireland tro my knowledge but they had plenty of it in Britain (slowly being converted to 2+1). It requires you to drive on the left and overtake in the middle 'suicide lane'. If people only overtake when it's safe to do so then S3 provides faster journeys as you won't generally be caught behind a tractor on the single lane side as can happen on 2+1. Unfortunately driver behaviour makes 2+1 preferable in many instances. There are issues even on 2+1 where drivers accelerate dangerously to 'cut in' front of that tractor just before the 2 lane section givew way to 1 lane to avoid being stuck behind a slow moving vehicle for a kilometre. It all works better in Sweden because the mentality is different.

unkel · 30-05-2006 11:58am

murphaph wrote:

The jury is still out on 2+1 in many quarters. If drivers all behaved in a responsible manner then S3 would be better than 2+1. We never had S3 in Ireland tro my knowledge but they had plenty of it in Britain

:eek:

I sure hope they'll never go back to S3. In theory they are fine but in practice they're utter carnage...

The last time I was on an S3 was nearly 20 years ago in France. IIRC it was the oldest road from Bordeaux in the southwest direction (towards Arcachon), which was superseded by both a newer Autoroute and a newer Route Nationale. In fact it is probably the only time I ever drove on an S3 myself

S3 was common in many countries many years ago, e.g. in the Netherlands most intercity national roads were S3. They were all replaced by motorways back in the 60s

unkel · 30-05-2006 12:31pm

Here's a pic of an S3 in the UK:

Victor · 30-05-2006 9:45pm

Parts of the N8 in Cork were / are effectively S3, but is it really just lots of climbing lane (actually signed "slow lanes") joined together.

murphaph · 30-05-2006 10:03pm

Climbing lanes are 2+1 configurations. A 'true' S3 looks like the picture unkel posted. No hatching, no prohibitions on overtaking from any lane. In theory it would be legal to overtake a car in the middle lane by overtaking it on the right most lane. So you could legally have all 3 cars headed the same direction stretching beside each other across the road. That's why they're so dangerous because people act the maggot on them. Shame really, they could be really useful.

Victor · 30-05-2006 10:14pm

That would be "interesting" with the curve in that picture. :eek:

Our man in Havana · 30-05-2006 10:30pm

There was a S3 section in Cork city for years heading out from Turners Cross towards the model farm road. Scary times! :eek:

Victor · 30-05-2006 10:35pm

Victoria Cross maybe? You mean Wilton Road? The lower section was 4-lane and the upper section was 2-lane (I think it later got a bus lane)

Our man in Havana · 30-05-2006 10:49pm

Yes indeed victor.

Still dangerous though.

Our man in Havana · 30-05-2006 11:05pm

Here is an S4 in Britain.

:eek: :eek:

Victor · 30-05-2006 11:16pm

Hmmm, odd that the central lanes look wider than the side lanes (where one expects more of the trucks).

nordydan · 30-05-2006 11:18pm

Victor wrote:

Hmmm, odd that the central lanes look wider than the side lanes (where one expects more of the trucks).

That's perspective Dougal. These cows are small, the others are far away!

jd · 30-05-2006 11:43pm

The use those S3's a bit in California. I think the road through 29 Palms/Joshua Tree from La is one in parts.

jd · 30-05-2006 11:49pm

jd wrote:

They use those S3's a bit in California. I think the road through 29 Palms/Joshua Tree from La is one in parts.

or even this (bit between yellow if for junctions)

Our man in Havana · 30-05-2006 11:57pm

Centre lane is for turns only.

jd · 31-05-2006 12:51am

Bond-007 wrote:

Centre lane is for turns only.

oops

Well I knew that in the case ab ove..

murphaph · 31-05-2006 10:32am

That pic shows the geatest thing about US road markings. In Europe the centre dividing line is always white, with maybe a different length/width than running lanes such as in that UK S4 example. This is potentially very hazardous as it's hard to tell what lanes run which way! The US solves this problem by marking any lane to the driver's left which runs against him with a yellow line rather than a white one. So obviously all US S2's are divided with a yellow line as the lane to your left is obvoulsy for oncoming traffic but on a freeway you'll see the markings are regular white ones like here. So simple but really effective.

unkel · 31-05-2006 11:21am

Bond-007 wrote:

Here is an S4 in Britain

Looks more like an S2 with hard shoulders to me, but I suppose technically you're right because of the interrupted lines

icdg · 31-05-2006 8:32pm

TO bring this back to its' original topic...there's a perhaps throwaway line in an article on the front page of today's Irish Times Motoring supplement about the NRA wanting legislation to reclassify dual carrigeways as motorways. Since this can be done under existing legislation - maybe they want legislation to make it able to be done easier (and not paying compensation...)

Chris_533976 · 01-06-2006 1:02pm

Good. They should be able to. I reckon the NRA can see how daft it is to have Motorway roads classed as DC. The 120kmh limit is hopefully a stopgap measure to make them effectively DC, while they go through the procedure of making them OFFICIALLY motorway.

Fool 5000 · 05-06-2006 7:57pm

Bump!

It seems that this change in speed limit will be rolled out throughout the country as soon as all the new interurbans are built.

The National Roads Authority (NRA) is considering raising speed limits on the dual carriageways that are located on the major inter-urban (MRU) routes from Galway to Dublin.

Sections of the Dublin to Galway MRU route are still under construction. At present, parts of it are designated as dual carriageways and sections are motorway. The NRA has revealed that it is considering raising the speed limit on certain sections of the dual carriageways from 100 kph to 120 kph.

The NRA is also considering what the speed limit will be on the Gort to Crusheen dual carriageway. The Compulsory Purchase Order (CPO) and the Environmental Impact Statement (EIS) sections of the project have been completed. The NRA is currently waiting for planning permission from the planning authorities. And a speed limit of 120 kph will be considered on the road when it is constructed.

A spokesperson for the NRA added, ?The existing ones (speed limits on dual carriageways) in the county would also be considered but there is very strict safety criteria that need to be looked at and that would be the number one priority.?

[Article] Dual-carriageway speed limit increased to 120kph

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