zig zag

Advantages

Zig zags tend to be cheaper to construct because the grades required are discontinuous. Civil engineers can generally find a series of shorter segments going back and forth up the side of a hill more easily and with less grading than they for continuous grade, which must contend with the larger-scale geography of the hills to be surmounted.

Disadvantages

Zig zags suffer from a number of limitations:

The length of trains is limited to what will fit on the shortest stub track in the zig zag. For that reason, the Lithgow Zig Zag's stubs were extended at great expense in 1908. Even then, delays were such that the zig zag had eventually to be bypassed by a new route, which opened two years later.

Reversing a locomotive-hauled train not purposely equipped for push-pull operation without first running the engine around to the rear of the train can be hazardous; however, operating the train with two locomotives, one at each end (a practice known as "topping-and-tailing"), can mitigate the dangers.

The need to stop the train after each segment, throw the switch, and reverse means that progress through the zig zag is slow.

Passenger cars with transverse seating force riders to travel in reverse for at least part of the journey though that issue is largely solved by longitudinal seating on cars serving such routes.

Hazards

If the wagons in a freight train are marshaled poorly, with a light vehicle located between heavier ones (particularly with buffer couplings), the move on the middle road of a zig zag can cause derailment of the light wagon.

Examples

Argentina

Tren a las Nubes (1921)

Australia

Lithgow Zig Zag, New South Wales (1869–1910) preserved – see Zig Zag Railway

Out of use:

Kalamunda Zig Zag, Western Australia – two reversals (dismantled)

Lake Margaret Tram, Tasmania, 610 mm (2 ft) (dismantled)

Lapstone Zig Zag, New South Wales – two reversals (1865) (dismantled)

Mundaring Weir branch railway, Western Australia (dismantled)

Thornleigh Zig Zag, New South Wales (dismantled)

Yarloop, Western Australia (dismantled)

Yarraglen (dismantled)

Chile

Pisagua – Three reversals; long out of use but earthworks easy to trace

China

Mifengyan on the Jiayang Coal Railway 762 mm (2 ft 6 in) – one reversal

Qinglongqiao on the Jingbao Railway

Czech Republic

Dubí – local railway between Moldava and Most (Most–Moldava railway), trains have to change direction in Dubí station to continue further. Only one half of a 'Z' is placed