Unlocking the “Britomart Bottleneck”
A key reason to construct the City Rail Link (CRL) project is to increase the capacity of the Auckland rail network. The current network consists of three main lines (the Western, Eastern and Southern) and two branch lines (Onehunga and Manukau), all of which converge on the Britomart train station. This is shown in the diagram below: As Britomart is a ‘dead-end’ terminal station, with all trains having to exit via the same two tracks they arrived on, there is a relatively low limit (approximately 21 trains per hour inbound) to the number of trains the station can handle. As Britomart station is by far the most popular station on the network, a bottleneck is created which limits the number of trains that can operate on the entire network. The track arrangement at Newmarket station also limits the capacity of the rail system, as Western Line trains must cross over other trains and perform a reversing manoeuvre.
The track bottleneck at Britomart, and the constraints this bottleneck puts on the network as a whole, means that Auckland cannot yet extract full value out of the extensive investment that has been undertaken in the rail network over the past decade. The introduction of electric trains from 2013 onwards will boost the passenger capacity of the network, but because the three main lines will still be ‘capped’ at six trains per hour, the rail network will still carry far fewer people than the maximum capacity of the lines. In short, the Britomart bottleneck is like having three motorways converge onto a cul-de-sac.
The City Rail Link, by turning that cul-de-sac into a ‘through route’, opens up the capacity of the entire network, ensuring we get value for money from the rail network and significantly enhancing the capacity of Auckland’s entire transport network. The City Rail Link creates a second rail entrance to the city centre (from Mt Eden), doubling the number of trains that can enter the city centre at any one time. Capacity is further increased through the reduction of conflicting movements on the rail network as trains do not have to ‘turn around’ and return the way they came – they can simply keep on going.
Increasing transport capacity to and through the city centre:
The pictures below illustrate the capacity increase (in people per hour) provided by the City Rail Link, with arrow width equivalent to the possible number of people per hour. (Further detail on the numbers behind the diagrams here).
- The lines represent places where people enter the CBD from, Red lines are access points from the motorways, Blue from local streets, Yellow from the ferries and Green is the rail network. The size of the line represent the number of people (not vehicles) coming via that route.
- For the streets the bus and vehicle counts are merged into one arrow, bus patronage is worked out at approx 30 people per bus for the current map, 40 per bus for the 2017 map and 50 people per bus for the 2022 map.
- For the rail network the current count only includes people entering Britomart so other heavily used stations like Grafton and Newmarket are not included which take up much of the reserve capacity. The final map only shows the network at 60% capacity with the assumption that people would still get off at stations like Newmarket.
Post Electrification: Post City Rail Link:It is important to note that the City Rail Link does not only increase the capacity of the rail system for trips to the city centre, but also vastly increases capacity across the entire network. Many more trains will be able to operate at much higher frequencies, benefiting travellers at any point along the rail system.
- The current rail system is constrained with only 21 trains per hour able to enter Britomart during the peak hour – meaning that frequencies on the three main lines (west, south and east) can never be improved from a train every 10 minutes.
- The CRL opens up the capacity of the whole rail network by creating a second entrance to the city centre at Mt Eden and allowing trains to travel through the city without having to turn back.
- The CRL reduces conflicting movements at Newmarket station, which otherwise constrain the capacity of the rail network.
- The CRL makes much higher frequency trains possible across the whole rail network, utilising past and present investment in that network to a greater extent.
- The CRL provides sufficient capacity to allow further expansion of the rail network in the future [more on this matter to be added]