Gradients and Curvature
From Kingston the line ran west along the coastal plain, within 50 feet (15.2 m) of sea level, for about 40 miles (64 km) before starting a gentle climb over 5.25 miles (8.45 km) from Bodles to 250 feet (76.2 m) near Lancaster Halt. From here there was a plateau for about 24.25 miles (39.03 km) to the Milk River and the start of the 20 miles (32 km) climb through Scotts Pass and Porus to 1,500 feet (457.2 m) just north of Kendal.
Between Kendal and Mile Gully the line reaches its summit at around 1,700 feet (518.2 m); in this section the ruling curvature was 300 feet (91.4 m) and the ruling gradient was 1 in 30 (3.33%).
From Mile Gully there was a gentle descent over 17 miles (27 km) to 500 feet (152.4 m) near Raheen. From here the line ran on the level across the Appleton Plain to Maggotty and the start of a climb to 1,000 feet (304.8 m) near Stonehenge. From here to Catadupa the line ran on the level then descended to 500 feet (152.4 m) at Seven River. Another level section brought it to Long Hill Tunnel and the final descent into Montego Bay.
Read more about this topic: Railways Of Jamaica: Kingston To Montego Bay