Myths & Reality #3

Back with another "Myths & Reality" post, this time I am going to be looking at the a pet hate for many self proclaimed 'urbanist' and that is the cul-de-sac.

Now I say self proclaimed as many of these folk have no formal qualifications related to urban planning but still feel they are they authority to tell others how the city should be. I'll admit that I'm not an urban planner either, however I do have many years of experience of designing transport infrastructure.

So back to today's myth:

Cul-de-sac

"Cul-de-sac's promote auto-dependency and make walking and cycling non-viable options of transport"

Background:

The background to this myth is that cul-de-sac's happens to appear in many auto-dependant suburban subdivisions that have been built in many places all over the world and so by coexistence have been accredited with the poor planning behind the subdivision as a whole.

The real issue here is that we have gone through a period of time where cities have grown under strict zoning laws that have prevented mixed use developments and have focused on building large swaths of residential land which is completely disconnected from commercial, industrial and municipal area and hence resulting in long journeys.

The Reality:

Although the cul-de-sac is accredited with promoting auto-mobile use, obesity and the decline of walking and cycling the reality is it does the complete opposite.

In the following image you can see the standard grid layout, what you will note is that it is rather dense and efficient being able to serve a large number of properties with a minimal number of roads.

The downside of this layout however is that you will get large amounts of traffic heading along every road. Due to every road being busy there will be significant disruption at every intersection as there will be no primary movement to take priority. There are no benefits from using one mode in comparison to another when you are looking at the distance needed to be travelled, you also wont find some routes that are more suited for pedestrians and cyclists and other more suited for cars and trucks.

The Grid - Hamilton

Looking at the more modern suburban layout I have the following image which is from an area of Hamilton developed in the 70s & 80s.

What you will notice here is that the road network has changed so that we now have semi-direct main roads and then various local roads that comprise of loops or cul-de-sac's. What this does is funnel the traffic onto the larger main roads leaving the local ones for the few people who live on them as opposed to the grid that had everyone driving along every road. So in the modern case the arterial road will likely have more traffic than any individual road in the grid layout, the majority of roads will actually have less traffic. In the case of the cul-de-sac it will have such a low amount of traffic you could happily let your kids learn to ride a bike out on the road when you wouldn't dream of doing such a thing on a grid road network.

The other benefit we have is that these developments tend to be focused around a community shopping centre or park, and when you look at the road network you will find the distance you need to walk or cycle to these places is significantly less than the distance you would need to drive due to various short-cuts being provided. In some cases you may only need to walk about 500m to get to the shops, whereas if you drove it could be as much as 2km. This also helps when it comes to running public transport services as the various short cuts give pedestrians easy access to the main road where the service would be running.

70s & 80s - Hamilton

Comparison:

So when you compare the two different layouts we find the following:

Grids:

• Every road is busy
• Travel distance the same for all modes of transport

Cul-de-sac's

• Busy main roads
• Quiet side streets
• Short journeys when walking or cycling
• Driving not effective for short drips

Myths & Reality #2

Today we have Part II of the "Myths @ Reality" series

You can locate Part I here.

For today we are going to look at what is quite possibly the most popular anti-road argument being.

"Building Roads Doesn't Reduce Congestion"

This one comes in multiple forms but the general idea is that when you build a new road or widen an existing road the reduction in congestion is only temporary and you quickly end up back where you were before. This implies that the work done to improve the road was a waste of time as congestion has not reduced and therefore there has been no benefit.

Background:

Like all myths and legends there is actual an element of truth to this claim; It is true that when you add more capacity to something that has unreleased demand that usage will go up, but the conclusions that there has been no benefit is completely misplaced.

In a previous post I elaborated on what congestion is and based on what was discussed there we can expect that when we upgrade a busy road to have more capacity more people will come start using that road.

What about Public Transport:

Although I have started off mentioning roads this same induced demand effect also effects Public Transport (PT), in fact you could argue that one of the main driving factors of PT usage is the inadequacy of capacity in other modes. For example, since the extensive and disruptive roadworks have been occurring on the Northwest Motorway there has been a notable uptake in rail usage on the western line.

However if you look at PT in isolation; If you had a given bus route that's operating one bus every 15mins, and each of these buses tends to be approaching its limits in terms of capacity you will find some potential users are being turned away. To increase the capacity you can start running buses every 10mins which will make life more comfortable for the existing users until the customers who were previously being turned away come back making the buses just as busy as before.

PT supporters will claim that it is cheaper to increase the capacity on PT routes as you have already done the hard part of building the road, however the issue here is that the costs of running a bus, rail or ferry service is directly related to the capacity you are operating.

The Myth and the Reality:

To test this claim, that when you build a new road you simply attract more users and leave things just as congested as before, we are going to look at the SH18 Upper Harbour Motorway here in Auckland.

This section of motorway was built during the mid to late 2000's and bypasses Hobsonville Road and Upper Harbour Drive. The way this road bypasses the old State Highway is actually very similar to when the Southern Motorway was built between 1950 and 1970 and how it bypassed Great South Road.

So this section of motorway was built in two sections:

1) Hobsonville Section - Bypassing Hobsonville Road 

2) Greenhithe Section - Bypassing Upper harbour Drive

Hobsonville Section:

Hobsonville Road 2010 = 37,000 vpd

Hobsonville Road 2014 = 6,700 vpd

SH18 Motorway 2014 = 35,000 vpd

Greenhithe Section:

Upper Harbvour Drive 2006 = 31,000 vpd

Upper Harbvour Drive 2012 = 4,500 vpd

SH18 Motorway 2014 = 43,700 vpd

So as you can see from the numbers above there has been a significant reduction, >80%, in traffic on the existing route. For those of you that are not familiar with this section of road, the existing road alignment was a two-lane two-way road which that was at its absolute limits of capacity presenting a hazardous environment for cyclists and locals and a very low Level of Service (LoS) for all users.

Biking along this road now is both quiet and pleasant with there being very few cars, nice views and an open environment.

Upper Harbour Drive - Google Maps

Here Comes the Induced Demand:

So the above Upper Harbour Drive section has had 8 years for the induced demand to come and fill up the released capacity, however it seems here we are with 85% traffic less traffic than before. The motorway meanwhile as been growing as can be expected due to the demand that was being held back by the existing route that was at capacity, this will also be driven by cross harbour traffic which is unable to cross the main harbour bridge which is also at capacity.

2010 = 31,100

2011 = 33,700 +8.3%

2012 = 38,900 +15.4%

2013 = 40,900 +5.1%

2014 = 43.700 +6.8%

So yes we can see that motorway is attracting more traffic, but what about the existing roads that have had their traffic flows reduced by over 80%. Well if Auckland stopped changing, the city stopped growing and new business stopped establishing quite possibly these traffic volumes would stay down, however this is not the case.

One of the reasons for building the new motorway through this section was that the existing roads were at capacity and therefore development was on hold. Now that all this new capacity has been opened up the area can now handle more people and business.

The planned growth is shown in the following image of the Northern Strategic Growth Area (NorSGA).

NorSGA - AT

Busted:

In terms of the short term, ie 5 years we can safely say this myth is busted, however one issue we have is that the people who make this claim never actually quantify any of their claims. If their talking about 20-50 year time frames I guess they are correct in that any arterial roads we built in a growing city have a good chance of getting congested, but it makes you wonder what they are arguing against.

Are they arguing against roads or are they arguing against growth?

In most cases the people who make this claim live in large metropolitans and their greatest joys come as by-products of large number of people and the concentrations of wealth found in a growing city yet it seems they don't appreciate that this growth comes with increased travel and therefore congestion for all modes of transport.

Myths & Reality #1

I'm going to start a little series on "Myths & Reality"

It's quite common to see these from a pro-PT anti-road point of view but I'm going to try and make this series cover both sides.

So to start things off here is Number 1.

"Roads are Designed to Eliminate Peak Hour Congestion and are Empty for the Rest of the Day"

This is a common one from the anti-road brigade and is generally used as an argument against road improvements and motorways as it is claimed they are significantly under utilised for most of the time.

The reality is we can't afford to design roads to eliminate the peak hour traffic congestion, what road designers do is design roads to "manage" peak hour congestion. This may very well mean that the average speed is reduced from 100km/h down to 70km/h but the aim is to keep traffic flowing smoothly and safely.

It is the inter-peak hours that we try and keep traffic flowing at optimal conditions.

The following photo shows the Northern Motorway on a Saturday afternoon. You can see here that there are quite a few cars and if it were a video you would note the traffic was flowing smoothly. It is however in a bit of a fragile state in that one crash could cause some real issues, and when you have 160,000 vehicles a day driving along a given section of road the chance of there being is crash is quite high. Given there are wide shoulders here the traffic impacts of a minor crash would be much less than what we have been seeing on the North-Western Motorway (SH1) where a single crash would bring this level of traffic to a stand still.

Northern Motorway (SH1) Weekend Traffic

The next photo shows the South-Eastern Motorway (SH20) on a Sunday afternoon. You can see here that the road is rather quiet and flowing completely smoothly. A minor crash here would be of little consequence in terms of the of traffic flows. This section of road gets about 70,000 vehicles a day and potentially you could question as to why it was recently upgraded from 2-lanes each way to 3-lanes each way. The simple answer to that is forward planning as in 2017 the Waterview Tunnel is expected to open which will result in another 60,000 vehicles driving this route every day.

South-Western Motorway (SH20) Weekend Traffic

So what does any of this have to do with designing roads to handle peak hour congestion?

Well basically these photos are showing the motorway operating in near optimal conditions. The Northern Motorway is a little too close to capacity and the South-Western is a quite a bit under.

When it comes to peak hour when there is two or three times more traffic however, the northern motorway will be in stop start condition and the south-western will be close to flow breakdown. In both cases one minor crash would result in significant delays.