Green Tracking of Light Rail in Auckland

Green tracking in Rotterdam, Holland

This is a guest post from Ed Clayton

While this post concerns how to develop a transport network that improves water quality, to do this first we need to look at the upcoming water reforms and why reliance on cars and e-vehicles is incompatible with ensuring clean freshwater for future generations.

Aotearoa New Zealand has a new national direction governing water management with the introduction of the Essential Freshwater reforms. This demands immediate improvement to our freshwater systems and the need to bring waterways to a healthy state within a generation. Te Mana o te Wai is the central concept of this and sets out the directions councils need to take to improve waterways. Key to this are the principles of governance and stewardship, where those with authority must prioritize (improving and enhancing where required) the health of waterways now and into the future to ensure the needs of future generations are sustained.

To give effect to Te Mana o te Wai councils must apply the hierarchies of obligation, being the following:

1. the health and well-being of water;
2. the health needs of people; and
3. the social, economic and cultural well-being of people and communities.

Following such directions, it can be reasonably interpreted that councils should take steps to ensure that infrastructure supports Te Mana o te Wai. For transport this means building infrastructure that firstly has low pollutant generation and secondly can actively treat pollutant loads through sequestering contaminants within its structure, ensuring any discharged water is filtered and cleaned before entering the receiving environment.

But our current transport paradigm is inherently polluting. Centering cars and private vehicles in our urban spaces creates swathes of impervious surfaces. This results in “Urban Stream Syndrome”, where paved areas create faster runoff, leading to streams that have higher flood peaks and more erosive power, transport more pollutants and sediment and have fewer species and less complex ecosystems. Compounding this is that the more we drive not only do we require more impervious surfaces to drive on, we increase the number of tyres. And tyres are major sources of heavy metals and microplastics. Tyres are 1-2% zinc oxide by weight, added during vulcanization to make tyres harder wearing and longer lasting. In Auckland zinc is a major contaminant in our marine receiving environments, where too much zinc creates toxic conditions for the little critters that are integral parts of the food web. And tyres also produce microplastics from wear and tear on road surfaces with it being estimated that 10% of all microplastics in the world’s oceans are directly sourced from tyre wear.

None of the above is new. Auckland Council recognizes that roads carrying more than 10,000 vehicles per day are high contaminant generating activities. To mitigate this, such roads should have treatment devices within the corridor that can do a mix of reducing pollution and runoff. Yet retrofitting existing roads is challenging because these treatments devices generally take up more room than is available without a drastic reshaping of the corridor. And changing our vehicle fleet from ICE cars to electric vehicles will not address tyre wear either.

Knowing that we need to improve our waterways and knowing that cars create toxic freshwater environments leads to incompatible outcomes. The requirements of Te Mana o te Wai legislation will place responsibilities on local government that creates conflict with building roads as normal. We need to ask the question “What would urban transport look like if the fundamental requirement was a net-gain in water quality?”

We may have an answer if we can build a light rail network that is integrated with engineered swales and biofiltration devices. Overseas, the use of “lawn tracking” in light rails is extensive in Europe and implemented in a range of other countries including China, the U.S.A and Australia. These tracks incorporate grasses and groundcover plants over infilled soil. Often the only visible parts of the light rail network will be the rails themselves and the overhead wires. Such designs have important benefits. Compared to a standard concrete light rail surface, they reduce the noise associated with light rail vehicle movement, lower urban heat island effects and have lower embedded emissions as there is less concrete used in construction. They improve air quality through helping filter airborne contaminants and help improve community wellbeing through increased visual green space. And most importantly for this discussion, they allow surface water to soak in, thereby removing contaminants and slowing stormwater runoff with studies showing up to 90% of rain falling within the rail corridor soaking in and being used by the plants. Yet these tracks are not designed with water quality outcomes as a priority. Usually, lawn tracks are built to delineate the light rail lines, stop cars from using them and provide aesthetic quality to local areas.

While the final alignment of Auckland light rail is yet to be decided, it is likely to go via either Sandringham Road or Dominion Road in the central isthmus before heading to Onehunga and then on to Mangere. This alignment will likely be adjacent to roads carrying between 15,000 and 25,000 vpd, all classified as high contaminant generating activities. In the isthmus, some of it overlies fractured basalt zones where stormwater is directed to soakage (and then to aquifers) or combined stormwater/sewer networks. These soakage systems feed the Meola and Motions Creeks catchments that in turn discharge to coastal areas under permanent swimming bans. Other areas have more standard stormwater systems that discharge directly to urban streams. Treatment for these roads is sporadic at best with gross pollutant traps only at a select few locations (usually not good enough to filter out microplastics and particulate bound contaminants such as zinc). Making a conscious decision to put water quality outcomes first means that we could build light rail with swales and raingardens that can treat all of the runoff from adjacent road surfaces.

How this might look is similar to the photos of overseas examples but with specific engineered soils designed to infiltrate and treat contaminants. Cross sections would be altered to drain water from road surfaces to a center running light rail line. Effective treatment trains would consist of vegetated swales for pre-treatment before discharge to raingardens, removing sediment in swales and ensuring efficient infiltration in the raingardens. Native plants could be used to provide a rough surface texture that slows water movement, keeping water visible at the surface when it rains and providing food for bees and pollinators when dry.  In areas where road stormwater discharges to streams and marine areas, we could remove contaminants generated from tyres. Where possible, clean water would soak to the aquifers below in much the same way as it does now, but at slower and more manageable rates. In places where the corridor has a wide margin, such as the section between Mt Roskill and Onehunga running adjacent to the motorway, trees could be planted to create a linear forest. We know that climate change is likely to deliver more extreme heat events that impact on rail systems, trees can create a more consistent microclimate that shade and protect the infrastructure.

#Trees. The option is not public transit or trees. It’s both: public transit AND trees, lots of trees. Citywide public transit & trees, less cars, more density, safe & enjoyable walking & riding bicycles to access BRTs, LRTs, and TREEs. pic.twitter.com/4gyYoZVgsC

— Penalosa_G (@Penalosa_G) July 10, 2021

As an example, to treat the 4.9 km stretch of Dominion Road between the two proposed stations at Mt Roskill Junction and Dominion Road Junction (see the proposed Dominion Road route map), only 1500 m of swales and 150 m of raingardens would be needed (assuming treatment efficiencies as described in Auckland Council’s GD01 document). And these would not be needed in a continuous stretch, rather short sections of treatment could be targeted at suitable areas with enough hard space in between for stations, vehicle crossings and intersections (although let’s face it, more is better!).

We could build such a system to tie into a revitalized Queen Street that has been returned to the Waihorotiu, making a green and blue space that, if extended to additional parts of the proposed light rail line, created a stunning biophilic linear transport network from the city center to Mangere.

Recreating the Waihorotiu stream that once flowed down the Queen St valley, has been on my mind for a few years. Artist Chris Dews has got me thinking of how we could imagine light rail gliding down Queen in a blue and green environment. pic.twitter.com/nAglweuFxQ

— Chris DARBY (@DarbyatCouncil) July 4, 2021

So how can we make this happen? Currently the Auckland Light Rail Establishment Unit is beginning to consult with the public. What this entails is not clear as well-deserved criticism has emphasized already. We may only have 6-months to seize this opportunity to create a sustainable light rail network that can achieve Te Mana o te Wai. This could be the example we need to put our freshwater systems first when we plan infrastructure. And it must be part of an urban design process that addresses not just the light rail line but the adjacent land use too. At a personal level these ideas need to be communicated as widely as possible so spread and share this post on social media. Tāmaki Makarau deserves great public transport. Let’s make it happen.

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