"Building new roads just makes people drive more"

"Traffic expands to fill available space." is a well known maxim.

Adding public transport does work in modal change (whatever about motorist congestion) - however, the public transport needs to take road space from car use.

But at what point do you stop?



Whatever the system, peak capacity is the most expensive capacity to add. That counts whether you are building a road, public transport or flipping burgers.

Let us say you are building a road. Each boundary, verge, drain, etc. costs €500 per linear metre of road (not square metre of road). To construct a traffic lane will cost €1,000 per metre of road. However, a roads get wider and wider, this €1,000 per metre of road increase by 10% for each additional lane to account for more complicated bridges, junctions, etc. In the table below a one lane (per side of road) road will cost €2,000.

However, if you add an extra lane to that 1 lane road, you don't increase effective capacity by 100% - you only increase effective capacity at peak times by 100%. For the rest of the day / week, you are creating vast amounts of unusable capacity. So, let us say, that each time you add a lane, the effective capacity of the new lane is 80% of the previous lane. So the capacity of the two lane road is 1,800.

So using these assumptions, the price of a two lane road might be worthwhile, but as you make the road wider and wider, it starts to get very expensive to add the capacity (capacity that doesn't get used) and your value for money goes through the floor.

The numbers used in this example won't hold for all roads, so be careful if reusing this example.

Lanes (per side of road) Cost per lane (per metre) Total cost per metre Capacity per lane Total capacity Cost per capacity
Lanes Cost per lane (per metre) Total cost per metre Capacity per lane Total capacity Cost per capacity on the extra lane
Boundaries only €1,000 €1,000 0x 0x -
1 €1,000 €2,000 1,000x 1,000x €2.00
2 €1,100 €3,100 800x 1,800x €3.88
3 €1,210 €4,310 640x 2,440x €6.73
4 €1,331 €5,641 512x 2,952x €11.02
5 €1,464 €7,105 410x 3,362x €17.35
6 €1,611 €8,716 328x 3,689x €26.60
7 €1,772 €10,487 262x 3,951x €40.01

Deleted User wrote: »

Think there might be an error in your total capacity column...

You are correct. Apologies, it was a long day.

Deleted User wrote: »

If the "Capacity per lane" is accurate then 4 lanes and 5 lane roads have an almost identical capacity and anything more than that actually has less capacity, a 7-lane road would have less capacity than 3-lane road. :P

I'm not sure where you ware coming from. More lanes, should in theory always add more capacity, but you have to realise that at 3am Tuesday morning having 7 lanes is a waste of resources.

Apologies if my error confused you.

Quazzie wrote: »

Am i correct in saying that using your table it costs €1000 per metre to construct a single lane road way but €9488(not sure where your figure of €10,487 comes from) for a seven lane highway. Is that correct.

You need to add the €1,000 for the boundaries, drainage, etc., so it would be €10,448 - the different is in the rounding of the cents.

Sure the for each additional lane it comes in lower overall rather than higher, since you the cost of getting services etc onto site is already allowed for in the first lane.

I'm not sure where you ware coming from. More lanes, will always cost more. By "services", do you mean the building contractor's overheads? In the life of a road these are modest. However, a two lane road can go in a lot more places in the landscape than a 10 lane road, due to rivers, buildings, ground undulations, junctions, etc.

Again, apologies if my error confused people.

Victor wrote: »

But at what point do you stop?



Whatever the system, peak capacity is the most expensive capacity to add. That counts whether you are building a road, public transport or flipping burgers.

You could argue that adding roads to deal with population increase has gone to far in that pic.

I would counter that it's a question of adding different parts to the transportation mix depending on the specific circumstances. E.g. in a small town or village, you can add traffic capacity to build your way out of a traffic problem and be satisfied that will deal with the problem. All the small/medium sized towns in Ireland that were bypassed would bear this out.

Of course, in a large city, it would be more accurate to say that you cannot plan on accommodating everyone, everywhere driving everywhere by car - Robert Moses tried this in New York and it was a spectacular failure.

But if Robert Moses was an extremist in one way, one also has to guard against extremists the other way, such as those who would pretend that the same things that "work" in London or Singapore are the solution for glorified large towns.

As for Dublin, the biggest deficiency is in public transport - my current commute is less than 5 miles but takes more than an hour, why? Because the city has been neglected in terms of its public transport system. In this context, it is understandable that people are using the M50 as a commuter motorway even though it's massively congested at commuter times - if the people stuck in traffic on the M50 and other roads in the capital had a decent public transport system including considerably more rapid transit, many of those people wouldn't be driving. Yet if my own work were a few miles further out, I would be joining them because by PT there would be no point.

I would argue that the same is true in your pic - the problem is a very large scale demand for transportation, and it is at this point that public/rapid transport should be the dominating factor.

Aard wrote: »

Highway 401 around Toronto can be fairly impressive.

This was originally built as D2M, of course, but they had the foresight to leave room for expansion.



It is now wider

On those parts of the Ontario 401 with collectors you are generally driving in a 4 lane carriageway, maybe 5 lanes. So not totally different from elsewhere, although of course it is a quad rather than dual carriageway. Also Canadians are reasonably responsible drivers, by international standards.

It is to varying degrees related to the topic discussed here. A large part of this problem is down to a lack of proper planning from all parties involved (both directly and indirectly). Such parties include but are not limited to administrative counties, railway providers and bus operators. To start off, when some previous plans were drawn up to create new town centers with surrounding satellite neighborhoods, very little seemed to be done in the way of planned public transport links.

An example of this is the ongoing developments where the Dun Laoghaire Golf Club used to be. It consists of a heavily underused quality bus corridor on Upper Glenageary Road complete with at least two disused bus stops. One is located beside Park Pointe just off Upper Glenageary Road while the other is located in Honey Park near it's entrance from Kill Avenue. When planning these bus stops, did Cosgrave Developments liaise with Dublin Bus to confirm that they would introduce a bus route or routes at some point in the future or was this merely an assumption?

As I am less than impressed with the efforts of the state run public transportation bodies to deliver on their promises, I would openly accept efforts by established or start-up transportation companies to provide services. Aircoach's parent operation, First Group, provide a myriad of services in the UK ranging from intercity railway to suburban bus services. In fact, many of them are casual commuter services like Dublin Bus.

The number of journeys made by car on an ever expanding network of roads is surely indicative of latent demand for a corresponding public transport service. The lack thereof gives cause to demand for further development of motorways or dual carriageways. As I pointed out in another thread which the aforementioned hyperlink brings you to, there needs to be something of an M50 for railway services. The desired effect of that would be to curb future increases in M50 usage as well as encouraging existing users to leave their cars at home.

Currently, the M50 is already bursting at the seams predominantly between the Ballymount Junction and the N4 and again around Ballymun. Further widening would result in compulsory purchase orders. As someone who uses the M50 to get to and from work, I can see that it is rapidly reaching breaking point. While I mostly travel against the flow of traffic, tailbacks between the N81 and Sandyford are a frequent occurrence in the AM. I would certainly consider using public transport if I didn't have to go into town to come out the other end which takes 4 hours out of my day.

For inter-suburban travel, cycling is being streamlined as a healthier and more sustainable way of combating the issue being discussed in this thread. Presumably, this is to slow down the current trend of increases in car journeys as well as a replacement for ones currently undertaken by car. As has been pointed out by a few posters on other threads, upwards of 10000 car journeys a day are a kilometer or less which is cause for concern. Having said that, I do still disagree with many of the measures being taken by the DMURS for this purpose as the Dutch have far better ways of doing this.