Otahuhu creates a bottleneck
Yesterday I wrote on Auckland Transport reviewing the case for Light Rail to the Airport and how heavy rail could make a come back into the mix (see: Airport Light Rail Case Study Contained Errors Prompting Review? Back to Heavy Rail?).
The basic premise was the following:
Someone asked me to do a Service Pattern for heavy rail if the Airport Line was to be the mode of the choice. So I gave it a shot and this is what I came up with:
- Dark Red (solid) = South to West (Papakura to Henderson) Line via the City Rail Line
- Dark Red (dash) = Pukekohe to Papakura extension of the South to West Line
- Blue (solid) = Eastern Loop both via Newmarket and the City Rail Link (goes both clockwise and counter-clockwise between Westfield and the City Rail Link)
- Blue (dash) = Pukekohe to Manukau via the Manukau South Line
- Black (dash) Henderson to the Airport via Newmarket and Otahuhu
- Dark Red = 10 trains per hour each direction (peak), 6 trains per hour each direction (off-peak)
- Pukekohe to Papakura extension is 50% of South-West main services (so 5 and 3 respectively meaning every second service on the South-West goes to or from Pukekohe)
- Eastern Loop = 5 trains per hour (every 12 minutes) all day, seven days a week. Note: Between Manukau and Westfield it means a total of ten trains per hour before either splitting or merging (depending on direction given the Eastern Loop runs both ways through the CRL) at the Westfield Junction)
- Pukekohe to Manukau via the South Link is every 20 minutes all day seven days a week (so 3 trains per hour each direction)
- Henderson to the Airport via Otahuhu = six trains per hour (every 10 mins) all day, seven days a week
Given the City Rail Link has a limit of 24 trains per hour each direction (I only got 20 with two lines) as well as other constraints elsewhere there are limitations to how much the heavy rail network can handle.
If you look between Westfield and Otahuhu I run into problems very quickly on rail capacity:
10 from the South-West, 10 from the Eastern Loop before the Split at Westfield and six from the Airport Line means I have 26 trains per hour each direction passing through what becomes a bottleneck. Now the Third Main from Westfield to Papakura with a third platform at Otahuhu gives me some room providing freight trains all go through the Westfield depot (Metro Port services can exit the Metro Port Southdown Facility straight onto the Southern Line at Westfield). It means a train is running through that section every 2:30mins across the three tracks. Now advanced rolling block signals as used overseas means we can achieve this kind of intensity on this short section of track.
The Fourth Main between Westfield and Wiri (although not sure how a fourth platform would fit at Otahuhu) gives breathing room and you probably could take the Airport Line to eight trains an hour although capacity constraints hit between Penrose and Newmarket.
Six trains an hour with each train holding 750 passengers (6-car set) means the Airport Line moves 4,500 passengers an hour. The Botany Line at 460 passengers (two 230 consists) every five minutes moves 5,520 passengers or some 1,000 more an hour. The Airport Line via Otahuhu would need to move at 10 trains per hour (7,500 passengers) and could be done if the Fourth Main is built and Otahuhu takes four platforms.
Can it be done? Yes but at an expense however.
Jury is out but remember a fully loaded six car set on the heavy rail network takes 566 cars off the road and if there is a train every ten minutes (6 TPH) that can mean 5,666 cars off the road.