Traffic Lights vs Roundabouts at busy urban junctions

veryangryman

Just wanting to see others take on these.

Personally, i think that if space is not an issue, roundabouts (even mini ones) should be placed at every current traffic light junction.

Some examples...

1) Athlone Crescent Junction. Formerly a roundabout that flowed quite well (save the buses going around it). Junction changed to traffic light with traffic islands when shopping centre opened. People (clearly p1ssed off with the junction) started using Mels Terrace as rat run, which was then closed. SAKE! Its the one bottleneck for me. Usually when going into town from Monksland, i take bypass to N55 exit and straight on, but this almost makes it worth using the old road in through the medieval town bridge.

2) Approach roads to Galway junctions (M6 to Headford Rd/Browne Roundabout). All roundabouts which could likely be improved with freeflow, but in lieu of that it beats the crap out of traffic lights. Browne roundabout can be busy so the lights are probably right there. Should shut them off outside of peak hours though

3) Newbridge in general. Stupid town traffic management system. Installing traffic lights like its going out of fashion. More roundabouts please!!

As per the recent replies by ATC on the proposals on alternatives to traffic lights at N6 J9, it seems like the lights are favoured to be more pedestrian friendly.

Pedestrians should not be given priority - the roads are paid for by car owners. Id even allow this if the lights only changed by request - some traffic lights let pedestrians go without pressing button - such a joke.

Id imagine most other roadwatchers here will favour the roundabouts - remember subject title - urban roads (so freeflow in this case is assumed not an option). Let me know what ye think anyway :pac:

Victor

Traffic lights are more efficient than roundabouts in peak flows.

veryangryman wrote: »

the roads are paid for by car owners.

By the way, how do you get from car to shop?

Yawns

Not until every driver in Ireland has been extensively tested for being competent to handle roundabouts. I live in an area where there is a mini roundabout with 3 exits. 1 is on a slight hill.

Drivers to not even bother to look to their immediate right coming down the hill. It's scary cos you can't see traffic coming until you close enough to the roundabout itself but these drivers just plow on down the hill and don't slow down or look regardless of signs. There's gonna be an awful crash there one day.

sdanseo

Ah sure it's Ireland - let's have BOTH at the same time!

AAaaarrrggh!

Stark

Yawns wrote: »

Not until every driver in Ireland has been extensively tested for being competent to handle roundabouts. I live in an area where there is a mini roundabout with 3 exits. 1 is on a slight hill.

They already include roundabouts on the driving test. In any case, people tend to go through roundabouts at fender bender speed as opposed to the 60-70km/hr that you often see people accelerate to in order to catch the end of an amber light. The consequences for getting it wrong are a good deal less. The downside is that roundabouts tend to be pretty gnarly for cyclists.

Traffic lights tend to be way overused imo. Very annoying being forced to wait at a red light to get out of somewhere where there's plenty of gaps in traffic that you could easily pull out into in far less time and with no disruption to the traffic flow on the main road. Granted the gaps are probably due to lights further up the road but having fewer sets would mean less frustrating driving conditions.

Yawns

People have enough problems grasping the concept of nice long stretches of motorways. Do you really think they can function on roundabouts at nearly every junction considering they can't use lanes correctly for approaching roundabouts as it is?

corktina

Victor wrote: »

Traffic lights are more efficient than roundabouts in peak flows.



is that an opinion or can you provide evidence? IMHO a roundabout USED BY COMPETANT DRIVERS, is way better than lights as it has no dead periods that are there whilst lights change.

To have lights on a roundabout (unless they are there to prevent tailbacks (on to a major rd perhaps) is proof positive that the average irish driver is incompetant.

murphaph

I don't have links but Victor is correct. Traffic lights permit more vehicles through a junction when that junction reaches a certain volume of traffic.

None of this is simple-it also depends on the balance of traffic on each arm of the junction etc. There are sophisticated traffic modelling software packages out there to help traffic engineers decide on the right setup.

At least traffic lights in Ireland often have an inductive detection loop that allows the lights to switch quickly from red in the dead of night. In Berlin they are almost non-existant and you have to sit and wait for the timed sequence 24 hours a day (unless they are part time signals-also quite rare in the city).

Stark

Yawns wrote: »

People have enough problems grasping the concept of nice long stretches of motorways. Do you really think they can function on roundabouts at nearly every junction considering they can't use lanes correctly for approaching roundabouts as it is?

Most people negotiate roundabouts without issue. Do you really think Ireland is the only country in the world that has bad drivers?

munchkin_utd

Stark wrote: »

Most people negotiate roundabouts without issue. Do you really think Ireland is the only country in the world that has bad drivers?

Nope, but it does have some well crazy roundabouts like the one in Galway at the shopping centre and the ones being fixed in Cork.

The lack of efficiency of these constructions is easily explained.
They are signalised so already the only real advantage of roundabouts is negated.
Then, you have trafic weaving about amonst each other as it negotiates the roundabout. This in itsself is a hinderance
Finally the clincher (if I can explain it clearly enough) is the slowness of ability to flush the traffic waiting before a junction - through the junction.

At a signalised roundabout you have 2 lanes of waiting traffic, 2 lanes around and 2 lanes of exiting (sometimes 3 but still.) So on a green light entering the junction - per second you are only "flushing" 2 lanes through the junction, and even then they can be jolty/ braking and swerving about the place changing lane on the roundabout.

At a signalised junction say where 2 dual carraigeways meet - you can have say 6 lanes (or more*) stacking before the junction and then "releasing" or flushing that much larger broad mass of cars per second through the junction upon green.

The all important factor is the number of cars you can flush through a junction in a sort period of time, and the roundabouts no matter how optimised (i.e. unfathomable for people not used to the shaggers) it will never be as performant as a well organised broad junction.

EDIT: heres a university paper with formulas and all which shows that for busy junctions (as per the thread title) a signalised junction will have more capacity than a roundabout.
http://www.strc.ch/conferences/2001/tan.pdf

serfboard

veryangryman wrote: »

2) Approach roads to Galway junctions (M6 to Headford Rd/Browne Roundabout). All roundabouts which could likely be improved with freeflow, but in lieu of that it beats the crap out of traffic lights. Browne roundabout can be busy so the lights are probably right there. Should shut them off outside of peak hours though

In the case of Galway, there is a proposal to replace a lot of the roundabouts with traffic lights in conjunction with a proper traffic management system, with cameras and a supervisor who can monitor junctions and change traffic lights to improve flow. If they do this, then I support the idea of replacing the roundabouts.

Stark

munchkin_utd wrote: »

Nope, but it does have some well crazy roundabouts like the one in Galway at the shopping centre and the ones being fixed in Cork.

The lack of efficiency of these constructions is easily explained.
They are signalised so already the only real advantage of roundabouts is negated.
Then, you have trafic weaving about amonst each other as it negotiates the roundabout. This in itsself is a hinderance
Finally the clincher (if I can explain it clearly enough) is the slowness of ability to flush the traffic waiting before a junction - through the junction.

At a signalised roundabout you have 2 lanes of waiting traffic, 2 lanes around and 2 lanes of exiting (sometimes 3 but still.) So on a green light entering the junction - per second you are only "flushing" 2 lanes through the junction, and even then they can be jolty/ braking and swerving about the place changing lane on the roundabout.

At a signalised junction say where 2 dual carraigeways meet - you can have say 6 lanes (or more*) stacking before the junction and then "releasing" or flushing that much larger broad mass of cars per second through the junction upon green.

The all important factor is the number of cars you can flush through a junction in a sort period of time, and the roundabouts no matter how optimised (i.e. unfathomable for people not used to the shaggers) it will never be as performant as a well organised broad junction.

EDIT: heres a university paper with formulas and all which shows that for busy junctions (as per the thread title) a signalised junction will have more capacity than a roundabout.
http://www.strc.ch/conferences/2001/tan.pdf

That traffic lights are better than roundabouts for junctions with heavy traffic flow was never in dispute as far as I'm concerned. What I do dispute is the assertion that you can't use roundabouts in areas with light traffic flow because people are too incompetent to use them. Until I see some evidence of serious accidents being more commonplace at roundabout junctions, that will continue to be my viewpoint.

AugustusMinimus

Why not go for both.

Signalised roundabouts give the best of both worlds.

When traffic is light, have the traffic lights on flashing amber. At peaks times, have the lights in operation, thereby increasing the capacity of the roundabout.

A lot of people don't like them but they work. Putting lights on the Dunkettle Interchange greatly helped the situation.


I can't prove it, but I'd imagine that a signalised roundabout would have a higher capacity that a signalised junction due to factors such as no cross over of traffic and the fact that a certain amount of traffic can be held on the roundabout itself at any one time.

Iwannahurl

veryangryman wrote: »

Pedestrians should not be given priority - the roads are paid for by car owners. Id even allow this if the lights only changed by request - some traffic lights let pedestrians go without pressing button - such a joke.

I was considering a reply until I read the bilge in bold above. Then I lost the will to respond to such garbage.

munchkin_utd

AugustusMinimus wrote: »

Why not go for both.

Signalised roundabouts give the best of both worlds.
.

Noooooooooooooooooooooooooooooooooooooooooo

I have mental visions of the Blanchardstown roundabout/ Shopping centre in Galway/ various magic roundabouts in Cork city that make me want to scream at the thought of signalised roundabouts.

A light on a roundabout as a tweak in a medium heavy traffic scenario is one thing.
But the way they are in Ireland is often a retro fit acknowledgement that the road designers did not build the right junction in the first place to cope with seriously heavy traffic.

Whether that HIGH CAPACITY junction is a freeflow flyover or a proper broad signalised junction.

corktina

the only reason that traffic lights on roundabouts in Ireland appear to improve the system is that incompetant irish drivers dont know how to use roundabouts properley and so sit there when the lights turn green for too long and change lane where they shouldnt causing a ripple effect delay behind them etc. If they learnt how to drive properley, roundabouts are much more effeicent.

I recall a roundabout from my youth in the UK, it was at a major junction of two trunk A roads and had 4 lanes coming on to it and around it, you took your life in your hands (or so it appeared) in pulling out on to it, but everyone used their mirrors and indicators and I dont ever recall a delay or an accident there.

Iwannahurl

What is it about the Irish obsession with roundabouts anyway?

Our enthusiasm for them seems to be in inverse proportion to our ability to justify, design, construct, maintain and use them.

I've just returned from a visit to Stockholm, a very busy European capital with a population of 851,155 in the municipality, 1.37 million in the urban area, and around 2.1 million in the 6,519 km2 metropolitan area (Wikipedia figures).

As a pedestrian, I encountered the sum total of one roundabout. That was on a busy distributor road near a betalstation (automated paypoint for the famous and highly effective Stockholm Congestion Tax) and on all arms it had crossings that gave priority to pedestrians and cyclists.

Irish roads engineers and Irish drivers deserve each other, unfortunately.





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antoobrien

I don't care what any theoretical figures say Traffic lights = bad traffic flow.

I'll give a couple of very simple examples from my experiences of traffic in Galway.

Claregalway generally has a 2 mile tailback due to the traffic lights in the village. When they're off the tailbacks happen after the village.

The junction on the headford road at the court house (courthouse sq I think) - traffic runs perfectly while the lights were out (granted its main use is as a pedestrian crossing so they can't be left off).

And finally the moneen - I haven't actually spoken to any motorist, cyclist or pedestrian who uses this road regularly that likes using this junction since it was converted to lights. One person told me that if they didn't work in the offices on the hill (no right turn) they would not use it going home. Most people I've talked to just say "avoid it like the plague" and go into a rant. Any time I have used it, (i.e. when I can't go to bohermore instead) it's taken several times longer than to negotiate than at any stage when it was a RAB, which kinda defeats the stated purpose of increasing traffic flow.

AugustusMinimus

corktina wrote: »

the only reason that traffic lights on roundabouts in Ireland appear to improve the system is that incompetant irish drivers dont know how to use roundabouts properley and so sit there when the lights turn green for too long and change lane where they shouldnt causing a ripple effect delay behind them etc. If they learnt how to drive properley, roundabouts are much more effeicent..

That is simply not true. Signalised roundabout have a far higher capacity as traffic flows much more smoothly.

When there are no lights, traffic must enter a roundabout haphazardly when gaps appear. This system doesn't allow traffic to be near as close together on the roundabout.

Unsignalised roundabouts with high traffic are an absolute mess as the traffic is non-laminar, compared to signalised traffic which would be described as laminar.

corktina

. If you want lights why have a roundabout at all. Stationary two or three times whilst gyrating is not efficent and the pauses whilst the ligths change cause delays.

And as for plain lights, In Mallow at the bridge at Christmas they turn off the lights to help the traffic flow...and it does!

niloc1951

Back in days long before ABS Airbags etc. etc. I learned how to negotiate roundabouts in rush hour when I regularly had to use the one on the end of Holland Park Avenue in Sheperds Bush (London).
If it wasn't part of your plan to have a picnic while waiting to get home you 'hit' the roundabout slowing just to the speed of the traffic circulating on it, and timed your arrival to slot into an arriving gap, often not much more than about one and a half car lengths and slipped off when you came to your exit.
The whole thing worked because, everyone use their indicators correctly and nobody blew horns when someone 'slipped in' half a car length in front of them, In fact it seemed like everyone seemed to be helping everyone else get home with as little delay as possible

How very mature and un-Irish.

marmurr1916

corktina wrote: »

the only reason that traffic lights on roundabouts in Ireland appear to improve the system is that incompetant irish drivers dont know how to use roundabouts properley and so sit there when the lights turn green for too long and change lane where they shouldnt causing a ripple effect delay behind them etc. If they learnt how to drive properley, roundabouts are much more effeicent.

I recall a roundabout from my youth in the UK, it was at a major junction of two trunk A roads and had 4 lanes coming on to it and around it, you took your life in your hands (or so it appeared) in pulling out on to it, but everyone used their mirrors and indicators and I dont ever recall a delay or an accident there.

I live in the UK and drivers here are no better. Most of the busiest local roundabouts have traffic lights which are either on permanently or switched on at rush hour.

Pretty much every major roundabout junction is clogged up at rush hour - one roundabout is so bad it can take over 40 minutes to get through. It's due to be replaced at some point by a grade-separated junction.

As for indicating and using mirrors (and giving way!) - drivers here are as bad as in Ireland.

I think the idea that Irish drivers are far worse than their British counterparts isn't really justified.

However, you're more likely to be caught driving badly and prosecuted in the UK than in Ireland. Drivers aren't the problem in Ireland - enforcement is.

AugustusMinimus

corktina wrote: »

. If you want lights why have a roundabout at all. Stationary two or three times whilst gyrating is not efficent and the pauses whilst the ligths change cause delays.

A roundabout allows more movements to occur at the same time vis-a-vis a flat junction. Allows more capacity.

In order for a non-signalised roundabout to have the same capacity as a signalised roundabout, it would require drivers to take incredibly rash decisions. It would prob be beyond human reflexes as the gaps would be required to be that tight to full it off.

Could you time it perfectly so that if you saw a car coming around a roundabout, that you would pull out at the exact time it would require you to accelerate to 50kph without having the other driver brake but also have about a 3m gap between you and the other driver when the manouver is over. This is what it would require.

Iwannahurl

antoobrien wrote: »

I don't care what any theoretical figures say Traffic lights = bad traffic flow.

I'll give a couple of very simple examples from my experiences of traffic in Galway.

Claregalway generally has a 2 mile tailback due to the traffic lights in the village. When they're off the tailbacks happen after the village.

The junction on the headford road at the court house (courthouse sq I think) - traffic runs perfectly while the lights were out (granted its main use is as a pedestrian crossing so they can't be left off).

And finally the moneen - I haven't actually spoken to any motorist, cyclist or pedestrian who uses this road regularly that likes using this junction since it was converted to lights. One person told me that if they didn't work in the offices on the hill (no right turn) they would not use it going home. Most people I've talked to just say "avoid it like the plague" and go into a rant. Any time I have used it, (i.e. when I can't go to bohermore instead) it's taken several times longer than to negotiate than at any stage when it was a RAB, which kinda defeats the stated purpose of increasing traffic flow.

1. Re "theoretical figures". Luckily motorists' anecdotes and perceptions are not the principal bases for traffic management and transport planning.

2. Re Claregalway tailbacks. Does it matter much where the tailbacks occur? AFAIK, the lights in Claregalway also have a pedestrian crossing function.

3. Re "traffic runs perfectly" when the signals near the Courthouse/Town Hall Theatre are off. How is such perfection of any use to pedestrians? EDIT: I see you have acknowledged this point already.

4. Re the Moneenageisha signalised junction. I used this junction a number of times very recently on trips in and out of Galway City centre. I much prefer it to the roundabout that was there previously, or indeed to any other roundabout I encounter when in Galway City. There, now you can no longer claim not to have communicated with a motorist/cyclist/pedestrian that has something positive to say about the new Moneenageisha junction.

5. I have just returned from Stockholm, a city with a much larger population, much higher population density and a higher rate of car ownership than Galway City. I encountered a single solitary roundabout and innumerable traffic lights, yet no "bad traffic flow" whatsoever. How does your anti-theory explain that?




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AugustusMinimus

Iwannahurl wrote: »

1. Re "theoretical figures". Luckily motorists' anecdotes and perceptions are not the principal bases for traffic management and transport planning.

2. Re Claregalway tailbacks. Does it matter much where the tailbacks occur? AFAIK, the lights in Claregalway also have a pedestrian crossing function.

3. Re "traffic runs perfectly" when the signals near the Courthouse/Town Hall Theatre are off. How is such perfection of any use to pedestrians? EDIT: I see you have acknowledged this point already.

4. Re the Moneenageisha signalised junction. I used this junction a number of times very recently on trips in and out of Galway City centre. I much prefer it to the roundabout that was there previously, or indeed to any other roundabout I encounter when in Galway City. There, now you can no longer claim not to have communicated with a motorist/cyclist/pedestrian that has something positive to say about the new Moneenageisha junction.

5. I have just returned from Stockholm, a city with a much larger population, much higher population density and a higher rate of car ownership than Galway City. I encountered a single solitary roundabout and innumerable traffic lights, yet no "bad traffic flow" whatsoever. How does your anti-theory explain that?




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Roundabout have huge benefits

1. Way more useful where low to medium traffic is experienced at a junction. No body gets held up.
2. Less petrol/diesel being burned, less CO2 released
3. Less chance of t-bone accidents which are about the most dangerous impact you can have.
4. Less accidents overall. Generally regarded as being safer overall.
5. Even in an urban setting, a roundabout looks much more attractive than a signalised junction.
6. Are cheaper to maintain


I think it says it all that in the most anti-roundabout country in the world (USA) that roundabouts are now becoming much more frequent. Various states, cities and towns realise the advantage of roundabouts over signalised junctions.

antoobrien

Iwannahurl wrote: »

5. I have just returned from Stockholm, a city with a much larger population, much higher population density and a higher rate of car ownership than Galway City. I encountered a single solitary roundabout and innumerable traffic lights, yet no "bad traffic flow" whatsoever. How does your anti-theory explain that?

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It might have something to do with the multi lane ring road around it and a somewhat reasonable PT system - though Galway city is so small it doesn't really need an extensive PT network ans Stockholm is the capital of Sweden.

Try a fair comparison, like oh say Dublin (which has proportionally the same population as Stockholm, if a slightly higher density) where there's massive tailbacks from traffic lights for most of the day, a (now) well functioning ring road and a fairly extensive (if aparently shambolically run) pt network as well.

Iwannahurl

AugustusMinimus wrote: »

Roundabout have huge benefits

1. Way more useful where low to medium traffic is experienced at a junction. No body gets held up.
2. Less petrol/diesel being burned, less CO2 released
3. Less chance of t-bone accidents which are about the most dangerous impact you can have.
4. Less accidents overall. Generally regarded as being safer overall.
5. Even in an urban setting, a roundabout looks much more attractive than a signalised junction.
6. Are cheaper to maintain


I think it says it all that in the most anti-roundabout country in the world (USA) that roundabouts are now becoming much more frequent. Various states, cities and towns realise the advantage of roundabouts over signalised junctions.

I think it says it all that in the most car-dependent and energy-wasting country in the world (USA) roundabouts are now becoming more common.

Relatively few roundabouts (certainly of the design common in Ireland) in European urban centres with relatively low levels of car use and high levels of active commuting. Please explain that, with reference to countries and cities where traffic congestion and transport policy are tackled sustainably.



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Iwannahurl

antoobrien wrote: »

It might have something to do with the multi lane ring road around it and a somewhat reasonable PT system - though Galway city is so small it doesn't really need an extensive PT network ans Stockholm is the capital of Sweden.

Try a fair comparison, like oh say Dublin (which has proportionally the same population as Stockholm, if a slightly higher density) where there's massive tailbacks from traffic lights for most of the day, a (now) well functioning ring road and a fairly extensive (if aparently shambolically run) pt network as well.

Stockholm is festooned with traffic signals. No traffic congestion that I could see (though there were hordes of visitors queueing for toilets!) and AFAIK congestion is not regarded as a problem there. They introduced a congestion tax in 2006 and took one in five cars out of the area inside the cordon.

They have almost no roundabouts in the urban zone where most people live and where most commerce, civic buildings, amenities etc are located.

Their public transport is excellent (an adult with a child in a buggy currently goes free, though that is under review).

Do you think there might be a connection between their deliberate policy to reduce car use, their use of bus priority measures and signalised junctions, and their low levels of traffic congestion?

Do you think they might be planning wholesale replacement of traffic signals with roundabouts to improve traffic flow?

Do you think the Swedes have much to learn from Irish roads engineers, urban "planners" and motoring interests?





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AugustusMinimus

Please tell me exactly what is wrong with roundabouts, and why these negatives outweight the positives I've listed.

I don't care about Stockholm. I've never been there and know nothing about the place. How can you be sure that traffic wouldn't flow even better in Stockholm if the signalised junctions were replaced with roundabouts for instance ?

Iwannahurl

AugustusMinimus wrote: »

Please tell me exactly what is wrong with roundabouts, and why these negatives outweight the positives I've listed.

I don't care about Stockholm. I've never been there and know nothing about the place. How can you be sure that traffic wouldn't flow even better in Stockholm if the signalised junctions were replaced with roundabouts for instance ?

You seem to care about the USA, though, for some reason.

Perhaps some Irish roads engineers should go on a professional visit to Stockholm, to enlighten them on how to fix their traffic problems with roundabouts. I'm sure the cloddish Swedes are just waiting to be rescued with some new cutting edge Irish engineering fixes that they never thought of, and no doubt they'll see the light when they're shown the achievements of a successful car-dependent country like Ireland. If there's a Galway City engineer on the delegation they can introduce the Swedes to the delighful practice of naming the revered roundabouts after mediaeval merchant families. Maybe they could even change the name of Stockholm's Ringvägen to the Claddagh Ring Road to immortalise the time they were saved by the Paddies...

Roundabouts cease to function properly in certain traffic conditions, eg when a dominant stream can lock up the junction at peak times. This is why traffic signals are retrofitted to some roundabouts, and why some roundabouts are replaced by signalised junctions, eg as is inevitably happening in Galway City.

Roundabouts, being uncontrolled junctions by design, do not allow the provision of bus priority measures or Adaptive Urban Traffic Control (AUTC) systems.

Roundabouts, of the design typically used in Ireland, are dangerous and intimidating for cyclists and pedestrians. Cyclists in particular face a greatly increased risk of collision.

Roundabouts, as seen in Ireland, are a barrier to bus users, since users of public transport are pedestrians at the start and end of their journeys.

Roundabouts, as used in Ireland, greatly favour private car use, though only in certain traffic conditions. Facilitating private car use at the expense of public transport, cycling and walking is not sustainable transport policy.

veryangryman

Iwannahurl wrote: »

You seem to care about the USA, though, for some reason.

Maybe hes been there? Or knows alot more about it than Sweden (most do), hence the caring