Longer slips add capacity. Junction design and spacing is the biggest factor in maintaining a road’s capacity. There’s a theoretical limit to trhoughput generally taken as 2000 cars per hour, per lane on a multi-lane divided road, but every time you come to a junction, you will reduce that throughput temporarily as traffic adjusts for leavers, passers-through and joiners.
If a car has to leap into the mainline from a short slip, anyone behind has to slow down. Give that joining traffic more space to build up speed, find a safe gap and merge in cleanly, and the new car will cause no disturbance to existing traffic. The same applies to cars leaving the mainline. If the exit slips are too short, then the queue to exit can extends into the mainline, and the leftmost lane of the mainline ends up being dragged down to whatever speed the exit junction can accept cars at. Longer (and wider) exit slips allow cars to leave the mainline at the same speed as surrounding cars.
J13 and J14 on M50 are what you have to do if your junctions are too close together to allow for acceptable merge and exit lane lengths. Here, the pair of junctions has been reconfigured to function as a single interchange. Doing this allows them to effectively share the same, longer length of sliproads, which gives traffic a lot more space to enter and leave. (The Bandon Road/Sarsfield Road junctions on Corks N40 are the same idea).
The reason that adding lanes for something like N3 won’t work is that through capacity isn’t the problem: junctions are. A series of closely-spaced juctions, onto 50km/h roads means that traffic never gets enough time to take advantage of an extra traffic lane, and also, a lot of traffic joins at one junction and leaves at the next, negating any advantage. The better solution is to separate the local and through traffic using a parallel access road, but there’s not enough space here to do so, as commercial premises are built right up to the road edge (same as with N7).
Closing the direct private entrances would do more for N3 than adding a lane each way.
That’s a bit obtuse. Longer exit slip lanes absolutely add capacity by preventing queues at the exit from affecting the mainline. The construction of a 2x2 lane DC between Dundrum and Sandyford along with the segregated on/off ramps also increases capacity on the motorway. Do you think they were built for the craic?
In either case, adding more lanes to urban roads does not help in the long run. It’s been proven time and time again.
The M50 is 4 lanes wide there, 6 to the west where there’s lane drops. You can’t count slip roads as capacity increases because they’re ultimately constrained by the capacity of the mainline.
I don’t believe that adding additional lanes will do anything positive. But there are plenty of other options once we remember that moving people is important, moving cars is not.
The idea that adding lanes to “fix” congestion is how you end up with 12 lane roads. You add more lanes, you get more congestion so you add more lanes. Each time you think this is the one that will fix it.
The M50 is already 8 lanes wide in parts and 12 if you consider the motorway and it’s ancillary roads around Sandyford. That €1bn that we spent a few years ago did very little to fix congestion.
Not for me, but a contiguous motorway network would be a good start.
🙄We need 12 lane highways like the utopia in the US, right?
Closing the gaps around Dublin in the radial motorways is a logical step. It's protects the routes from unwise adjacent development with access and enhances safety.
I'm really not bothered if the 3-laning happens or not. I'm more interested in the junction upgrades and closure of bad access arrangements. If that was all they ended up building I'd be happy.
However I'm not happy they are keeping the left-in-left-out at Parslickstown. This was never a good enough arrangement and the roads here should have fed into the nearby grade-separated junction. Here's a quote from the Existing Junction Analysis Appendix:
"It is proposed to retain Parslickstown Junction with only minor alignment changes to the traffic island to facilitate three lanes on the main carriageway. The closure of private entrances along the N3 corridor is to be carried out by providing alternative access arrangements to the rear of the properties and land holdings (See Figure 4.2). The closure of these entrances is necessary so as to not prejudice the re-classification of the N3 to motorway.
However, other departures from standard resulting from the proximity of Junction 4a will be required to retain the junction layout in general if the N3 is to be designated as a motorway eastward beyond the existing end of motorway at Junction 4a."
This is interesting as I'd been hoping they would reclassify Clonee-M50 as motorway but didn't know they were still considering it.
The extra lanes here are critical and fully justified. It doesn't go far enough but we'll take it for now.
No motorway, which presumably this will be redesignated to, should have two lanes in the GDA. 3 minimum.
So the Option Selection Report for N3 M50 to Clonee has now been published. This is the justification for adding another traffic lane in the hope of solving congestion, this is one report which is well suited to its future role as a dust collector on a shelf, unfortunately it will be joining other reports which should be actioned.
About the only positive thing I can see there (and I haven't looked too closely) is the proposed closure of private entrances along the N3.
Seth Brundle wrote: » A taxi replacing someone needing to own a car is not the same as creating a false entitlement for that taxi to use a bus lane.
Sam Russell wrote: » But those car sharing cars (GoCar) can park legally in Dublin for free, so quite an incentive. If their numbers of cars and subscribers were to increase to the level where they operate like Dublin Bikes, they become more user friendly. It then becomes used for going from A to B instead of A to B and back to A before the driver can sign off. I think they could transform city traffic, along with the e-scooter. All that is needed then is Metro, and congestion charging.
KrisW1001 wrote: » It’s my opinion that the availability of taxis reduces demand for private parking in city centres, but it shouldn’t be hard to see why. Take fast taxi journeys out of the picture, and city dwellers will find themselves pushed into buying a car for those occasional trips that are difficult to make on scheduled public transport. That car will then spend most of its time parked somewhere.
markpb wrote: » People without cars can still take taxis that drive in normal lanes. I understand that taxis being able to use the bus lanes is an appealing thing but people are also happy to use car sharing businesses in lieu of car ownership and those cars aren't allowed drive in bus lanes.
Seth Brundle wrote: » Is there any actual evidence that they are important and reduce private car parking or is this your opinion?
markpb wrote: » Those two buses could be carrying over 200 people. Plus: queueing theory, it’s not as intuitive as it seems. Do you believe that a slow-but-moving M50 is an efficient use of road space?
KrisW1001 wrote: » Allowing taxis to use bus lanes reduces demand for private-car parking in cities, where land is expensive and could be put to more productive use. Taxis are an important part of a public transport system, as they fill the short, point-to-point journeys that scheduled bus services can’t.
Aontachtoir wrote: » Besides, isn't a bus lane sitting relatively unused a waste of road space? There will be a bus or two passing every few minutes, sure, but the rest of the time the lane will sit empty even if the other lanes are immobile
Aontachtoir wrote: » I don't think anyone is saying that cars should be able to use bus lanes regardless of occupancy, only cars with a certain number of passengers. Two lanes is not enough for a major artery that carries thousands of commuters. That's why we're discussing widening the road.
Aontachtoir wrote: » Besides, isn't a bus lane sitting relatively unused a waste of road space? There will be a bus or two passing every few minutes, sure, but the rest of the time the lane will sit empty even if the other lanes are immobile. That doesn't seem like the most efficient use of space. Giving some benefits to HOVs would help to increase passenger density in private cars. If enforcement is a problem, then invest in enforcement. A couple of highly visible cameras and high fines will help nicely.
Pete_Cavan wrote: » Surely the logical thing for the N3 between Clonee and M50 would be to have a dedicated bus lane, a HOV lane and a general traffic lane. It could operate at peak times only. Suggesting that cars, regardless of occupancy, should be allowed to use a bus lane when they already have two lanes available to them is beyond stupid.
markpb wrote: » It’s a demonstrably terrible idea. Three cars with four people takes up more road space than a bus with over one hundred people. It wouldn’t take many cars in the bus lane to cause congestion holding up the bus or buses behind. That’s before you factor in the piss-takers abusing it and the waste of AGS time enforcing it. Then the delay and danger to cyclists who are also trying to use the bus lane and the additional lane changes at junctions when non-HOV cars are trying to merge in to turn left.
The Dark Knight wrote: » There are stories for people using blow up dolls in carpool lanes in the US. But.....€500 fines for breaking the rules may help with enforcement here. I think it's a great idea and we should have done this years ago. 4 people = use bus lane at peak times.
spacetweek wrote: » Too hard to enforce and people would take the piss.....
Aontachtoir wrote: » I would also suggest looking into allowing non-single user cars (at least 2 or 3 occupants) to use bus lanes. We already allow taxis to use bus lanes, so if the problem with private cars is low capacity (and I accept that as a valid criticism), then incentivise increased passenger density in private cars.
Aontachtoir wrote: » II would also suggest looking into allowing non-single user cars (at least 2 or 3 occupants) to use bus lanes. We already allow taxis to use bus lanes, so if the problem with private cars is low capacity (and I accept that as a valid criticism), then incentivise increased passenger density in private cars.
Aontachtoir wrote: » If the people of Dublin oppose both tree cutting and taking away road space, why does this mean that we must take away road space? Cut down trees and dig up gardens as needed, like Bus Connects originally called for before being watered down.
cgcsb wrote: » People in Dublin have generally responded negatively to tree cutting and positively re-allocating road space to bus and cycleways. There is often little choice in Dublin. Most roads can't be widened so the space has to come from the least efficient road user.
KrisW1001 wrote: » We are talking about the N3 Clonee to M50 here. The majority of journeys using this stretch of road will terminate in Dublin city at locations already served by buses. But it's pretty clear you don't agree, so speak up: what would you do to improve the current situation here?
