Maymorn - Kaitoke

The proposed Rimutaka Incline Railway route would start at Maymorn station, connecting with the Tranz Rail network. Old and new routes were connected via a tortuous temporary alignment, traces of which can still be detected today. A new connection is proposed, conforming to the ruling gradient and curvature of the rest of the route.

The railway climbed out of the Mangaroa valley, heading northeast to the valley of the Pakuratahi River. Reverse curves of 5 chain (100 metre) radius were used to keep earthworks to a minimum. An initial gradient of 1 in 50 steepened to 1 in 41 on entering the 242 yard (221 metre) Mangaroa Tunnel.

The gradient relented slightly to 1 in 53 on exiting the tunnel, curving through an 8 chain (160 metre) radius curve and heading south-east for four chains (80 metres). Collins Stream was crossed by a bridge consisting of four 20-foot spans, recently (2002) replaced by a concrete pipe culvert, the formation excavated to a lower level. A roadway occupies the former horseshoe curve of 5 chain (100 metre) radius, used for public access to Tunnel Gully Reserve, and utility access to radio transmission equipment on Mount Climie. A short 6 foot (1.8 metre) bridge is located towards the end of the curve.

The formation continues northwards through a couple of shallow 9 chain radius curves, the public road parting company as more 5 chain radius curves are encountered. For the next mile, heavy curvature and gradients characterise the route. Eight 5 chain and one 6 chain radius curves take up 45 of the 80 chains, whilst a gradient of 1 in 40 flattens slightly to 1 in 42 for the second half mile. The longest 5 chain radius curve of 11 chains length or 130 degrees is located in a deep waterlogged cutting that must have given trouble both during construction and service.

The watershed between Collins Stream and Pakuratahi River catchments is surmounted 28 chains (560 metres) short of Kaitoke station. The final approach to the station is made on a gently falling 1 in 660 gradient, with reverse 5 and 6 chain radius curves.

Main features

• 242 yard (221 metre) Mangaroa tunnel on 1 in 41 gradient
• Proximity to the Rimutaka tunnel and deviation at Maymorn
• Steep, incessant gradients, typically 1 in 40 - 45
• 40% of section length in tight 5 chains (100 metres) radius curvature
• Three bridges of single 6', 12' and 19' length spans on masonry abutments