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M7/M8 Portlaoise-Castletown-Cullahill Motorway (incl. Abbeyleix Bypass)
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Um, 4 years late.THE multi-million euro in M7 and M8 motorways could be open by the end of May, with an NRA spokesperson confirming that they are a number of months ahead of schedule.
Naas?Construction of the remaining section of the M8 motorway commenced in June 2007. This final section will run south of Portlaoise, where it will diverge from the M7 as the M8. The project, officially known as the Portlaoise-Castletown-Cullahill PPP Scheme, will extend from Naas in County Kildare to the northern terminus of the Dunkettle-Cullahill segment of the current M8 (the scheme also extends the M7 from Portlaoise to Castletown).
It won't be much use for Waterford-Roscommon other than removing congestion from those towns. Its connected to the "Athlone motorway" by the M50.Bypassing Abbeyleix will be a great help when travelling up to Roscommon. I assume there will be no connection to the Athlone motorway from the M8?
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Moderators, Education Moderators, Technology & Internet Moderators, Regional South East Moderators Posts: 24,056 Mod ✭✭✭✭
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It won't be much use for Waterford-Roscommon other than removing congestion from those towns. Its connected to the "Athlone motorway" by the M50.
Oh right, so we cant use the bypass unless your actually on the motorway?
You know me, looking for ways to avoid the normal national routes and stick to motorways as much as possible.
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Chris_5339762 wrote: »Out of interest, WHY is Abbeyleix such a bottleneck? Passing through it yesterday off-peak there didnt seem to be any specific pinch point that would slow traffic down enough to jam.
The set of traffic lights generally does it.
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Chris_5339762 wrote: »Out of interest, WHY is Abbeyleix such a bottleneck? Passing through it yesterday off-peak there didnt seem to be any specific pinch point that would slow traffic down enough to jam.
Among other reasons,
- because it has a set of traffic lights giving flow to another road
- because of the distance between either end of the town when driving on the N8.
In simplified Queue Theory:
l is the rate of arrival of cars to the town
m is the rate at which the town can process one through car
if l > m, a queue builds i.e cars will start slowing down before the beginning of the town (50 kph sign). Think of a sink with a slow blockage. If the rate of water coming out of the taps is higher than the rate the plughole can handle, the sink starts to fill a bit and you have to adjust the flow of the taps.
With the lights, the average time it takes to get through the town increases dramatically. 1/m is the average time through the town. Say the lights (on average - some have to stop, some don't) increase the time to get through town by 50%. This would mean 1/m increases by 50% to 3/2m
That means the rate that cars are processed through the village decreases by one third in this example.
So the time added by the lights, along with a high rate of cars approaching the village at peak times, significantly increases the average time to get through the village.
If it wasn't for the lights, the hold up would be similar to Urlingford in the old days - slow but moving - only it would be a bit worse as the distance between the 50kph sign entering the town and the 100kph leaving is longer in the case of Abbeyleix.
Of course, this is a bit over-simplified as in reality there are a number of systems in series - the overall town queue system is a series of minor systems involving the lights, the stretch where you let locals out of the parking spaces, etc. Also, the lights do not operate continuously, instead processing batches of jobs (cars) between intermittent idle periods (from the N8's perspective)
In short:
- greater arrival rate of cars than town's processing rate of through cars means a queue
- traffic lights reduce town's process rate for through cars
- queue continues to grow for as long as arrival rate of cars is higher than town's processing rate
- queue starts to shrink when arrival rate of cars slows down.
Simples 0 -
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Among other reasons,
- because it has a set of traffic lights giving flow to another road
- because of the distance between either end of the town when driving on the N8.
In simplified Queue Theory:
l is the rate of arrival of cars to the town
m is the rate at which the town can process one through car
if l > m, a queue builds i.e cars will start slowing down before the beginning of the town (50 kph sign). Think of a sink with a slow blockage. If the rate of water coming out of the taps is higher than the rate the plughole can handle, the sink starts to fill a bit and you have to adjust the flow of the taps.
With the lights, the average time it takes to get through the town increases dramatically. 1/m is the average time through the town. Say the lights (on average - some have to stop, some don't) increase the time to get through town by 50%. This would mean 1/m increases by 50% to 3/2m
That means the rate that cars are processed through the village decreases by one third in this example.
So the time added by the lights, along with a high rate of cars approaching the village at peak times, significantly increases the average time to get through the village.
If it wasn't for the lights, the hold up would be similar to Urlingford in the old days - slow but moving - only it would be a bit worse as the distance between the 50kph sign entering the town and the 100kph leaving is longer in the case of Abbeyleix.
Of course, this is a bit over-simplified as in reality there are a number of systems in series - the overall town queue system is a series of minor systems involving the lights, the stretch where you let locals out of the parking spaces, etc. Also, the lights do not operate continuously, instead processing batches of jobs (cars) between intermittent idle periods (from the N8's perspective)
In short:
- greater arrival rate of cars than town's processing rate of through cars means a queue
- traffic lights reduce town's process rate for through cars
- queue continues to grow for as long as arrival rate of cars is higher than town's processing rate
- queue starts to shrink when arrival rate of cars slows down.
Simples
Thank you Mr. James May !0 -
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Among other reasons,
- because it has a set of traffic lights giving flow to another road
- because of the distance between either end of the town when driving on the N8.
In simplified Queue Theory:
l is the rate of arrival of cars to the town
m is the rate at which the town can process one through car
if l > m, a queue builds i.e cars will start slowing down before the beginning of the town (50 kph sign). Think of a sink with a slow blockage. If the rate of water coming out of the taps is higher than the rate the plughole can handle, the sink starts to fill a bit and you have to adjust the flow of the taps.
With the lights, the average time it takes to get through the town increases dramatically. 1/m is the average time through the town. Say the lights (on average - some have to stop, some don't) increase the time to get through town by 50%. This would mean 1/m increases by 50% to 3/2m
That means the rate that cars are processed through the village decreases by one third in this example.
So the time added by the lights, along with a high rate of cars approaching the village at peak times, significantly increases the average time to get through the village.
If it wasn't for the lights, the hold up would be similar to Urlingford in the old days - slow but moving - only it would be a bit worse as the distance between the 50kph sign entering the town and the 100kph leaving is longer in the case of Abbeyleix.
Of course, this is a bit over-simplified as in reality there are a number of systems in series - the overall town queue system is a series of minor systems involving the lights, the stretch where you let locals out of the parking spaces, etc. Also, the lights do not operate continuously, instead processing batches of jobs (cars) between intermittent idle periods (from the N8's perspective)
In short:
- greater arrival rate of cars than town's processing rate of through cars means a queue
- traffic lights reduce town's process rate for through cars
- queue continues to grow for as long as arrival rate of cars is higher than town's processing rate
- queue starts to shrink when arrival rate of cars slows down.
Simples
Queue theory - the sport of kings! 0 -
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