As we know which has been covered in this blog in various forms previously, we do have an interest here in rail suburban passenger services on the Christchurch-Rolleston and Christchurch-Rangiora rail corridors.
The current pattern of urban development in Greater Christchurch is impacted by the location of Christchurch International Airport and the imposition of noise corridors on the axes of the airport’s runways. The traditionally used noise contour corridor imposed is labelled “50 dB Ldn” or similar and extends over most of the rail corridor from Islington to Rolleston, and from the north bank of the Waimakariri River to Kaiapoi. The noise corridor is influenced by the commercial imperative of Christchurch International Airport Ltd (75% owned by Christchurch City Council vial CCHL) which strongly asserts the airport should be operable 24/7 without curfews. These assumptions have been challenged numerous times in the Courts and in the recent Recovery Planning processes followed after the Christchurch quakes. These have resulted in a small relaxation in the noise contour over Rolleston and some limited additional development being permitted in Kaiapoi but the bulk of the zoning remains unchanged. In future the question of whether the imposition of curfews would be unduly onerous will no doubt come up as it has already many times.
The key question therefore is how the imposition of these contours will affect the future development of the area along with the prospects of rail passenger services. It is an unfortunate reality that the alignment of the north-south runway at Christchurch International Airport is nearly parallel to the Main South Line rail corridor between Islington and Rolleston and therefore overlaps it significantly, partly due to the curve in the corridor just past Islington where it changes from a due west heading to a south west heading. In practical terms of the railway geography, the limited area encompasses around 10 km of the Main South Line corridor. When we’re referring to the total distance from Christchurch out to Rolleston, this is about half of the total distance to Rolleston and is therefore quite significant. Development right along the edges of the rail corridor is therefore restricted at the current time. However the noise corridor is relatively narrow at the point where it most overlaps the rail corridor, being based on the assumption that aircraft will navigate on strict headings and altitude limits for short final approaches to the main north-south runway.
As far as the practicality of rail development on the Main South Line corridor goes, it would be impractical to develop residentially on both sides of the corridor from about 21 to 31 km milepegs. This is quite a substantial chunk out of the 22 km of the distance from Christchurch to Rolleston and does create a significant impact on the prospect for suburban trains being able to serve enough population. To overcome the impact of this 10 km of no residential population, the area of southern Rolleston would need to be able to develop to a much larger population than currently to make up for the loss of the population along that 10 km. The township of Templeton is entirely within the noise corridor and presumably is limited to its existing boundaries.
The impact on the northern corridor is somewhat less due to it being nearly at right angles to the north-south runway axis at the point where the noise corridor mostly impacts. This is due to the way the rail corridor curves around from north-easterly to north-westerly for a period, almost a 90 degree turn, just south of the Waimakariri River, in order to line up with Kaiapoi and Rangiora, before crossing the Ashley River and turning due east for a period and then back to north-east. Due to the proximity of the Waimakariri River and other waterways the practical impact of the corridor would be to limit development from about the 15 km milepeg to about 22 km. The main difference is that there is already development under the noise corridor which has been expanded since the quakes in the city of Kaiapoi and this means that Kaiapoi can be extended on its northern boundary just as Rangiora expands south.
I’ll take a more indepth look at the differences between the North and South rail corridors as far as these factors along with some operational questions for the rail line itself are to be considered.