Gauges & Tracks — Set 4

Correct Answer: C. Inner faces of the rails

• **Inner faces of the rails** = The gauge is the minimum distance measured between the inner running faces of the two rails, taken at a point 14 mm below the top of the rail head. This precise measurement ensures the wheel flanges of rolling stock fit correctly and the train runs safely. • **Why inner face matters** — measuring from the inner face (not the outer or top) accounts for the actual contact zone where the wheel flange bears against the rail, making it the only measurement that defines effective track width. • This standard is set by international bodies; in India, the Railway Board mandates gauge tolerances of ±6 mm for Broad Gauge to prevent derailment from excessive or insufficient clearance. • 💡 Option A (Top of the rails) is wrong because the rail top is the running surface for the wheel tread, not the reference face for gauge measurement; Option B (Center of the rails) is wrong because the centerline is irrelevant — wheel flanges engage the inner face only; Option D (Outer faces of the rails) is wrong because the outer face is farther apart and does not relate to where the wheel flange contacts the rail.

Correct Answer: C. Standard Gauge

• **Standard Gauge (1435 mm)** = It is used by approximately 60% of the world's railway network, including mainline networks of the USA, China, Canada, most of Europe, and Australia's interstate network. Its global dominance makes it the de facto international standard for rail interoperability. • **Origin** — The 1435 mm dimension (4 ft 8½ in) was adopted from early British colliery wagon tramways standardised by George Stephenson; the Gauge Act of 1846 in Great Britain formally established it, and it spread worldwide through British colonial and commercial influence. • In India, Standard Gauge is used in urban Metro systems (Delhi, Mumbai, Hyderabad) and the upcoming Mumbai–Ahmedabad High-Speed Rail corridor, but the mainline Indian Railways network uses Broad Gauge (1676 mm). • 💡 Option A (Broad Gauge) is wrong because at 1676 mm it covers only a fraction of the world network (mainly India, Pakistan, Bangladesh, Argentina); Option B (Meter Gauge) is wrong because its share of global networks is small and it is being phased out in India; Option D (Narrow Gauge) is wrong because it is used mainly for mountain railways and specialty heritage lines, not the global majority.

Correct Answer: B. Higher stability and speed

• **Higher stability and speed** = Broad Gauge's wider track base (1676 mm in India) lowers the centre of gravity and increases the lateral stability of coaches and wagons, allowing trains to safely run at much higher speeds without risk of overturning. This is why Indian Railways high-speed freight and express trains all operate on Broad Gauge. • **Key engineering fact** — Broader gauge permits wider coach bodies (3.66 m in India vs 2.74 m on narrow gauge), increasing seating capacity per coach by about 30–40% and enabling heavier axle loads, which directly raises freight revenue per trip. • Narrow Gauge is cheaper to construct because it requires less earthwork, smaller tunnels, and lighter materials — making it suitable for hill terrains — but this comes at the cost of much lower speed limits (typically 30–45 km/h) and restricted traffic capacity. • 💡 Option A (Lower cost) is wrong because Broad Gauge is significantly more expensive to build due to wider cuttings, heavier rails, and larger bridges; Option C (Easier mountain climbing) is wrong because Narrow Gauge is actually preferred for steep gradients since it requires less space for curves; Option D (Less steel used) is wrong because Broad Gauge uses heavier, wider rails and more steel per kilometre than Narrow Gauge.

Correct Answer: C. Thermit Welding

• **Thermit Welding** = It is the process of joining two rail ends by pouring molten steel produced by the exothermic reaction of aluminium powder and iron oxide (Thermit mixture) into a mould placed around the rail gap. Temperatures in the reaction reach about 2500 °C, fusing the rail ends into a seamless joint. • **Continuous Welded Rail (CWR)** — The result of thermit welding is CWR, where individual 13-metre rail lengths are joined into continuous lengths of 250–500 m. CWR eliminates the rhythmic 'clickety-clack' sound at joints, reduces wear on wheels and rails, and allows speeds above 160 km/h that would be unsafe on jointed tracks. • Indian Railways began large-scale thermit welding in the 1980s; today over 70% of the Broad Gauge network consists of CWR, significantly cutting maintenance costs. • 💡 Option A (Bolting) is wrong because bolting uses fish bolts through fishplates to connect rails mechanically — it does not fuse the metal and leaves an expansion gap; Option B (Riveting) is wrong because riveting is used in structural steel fabrication, not rail joining; Option D (Soldering) is wrong because soldering uses low-temperature alloys (below 450 °C) meant for electrical joints, far too weak for rail loads.

Correct Answer: B. Maharashtra

• **Maharashtra** = The Matheran Hill Railway is located entirely in Raigad district, Maharashtra, running 21 km from Neral Junction to the hill station of Matheran at an altitude of 800 m. It is one of the few surviving 2 ft (610 mm) Narrow Gauge mountain railways in India. • **Heritage and unique features** — Matheran is a no-vehicle zone, making the Light Railway the only mechanised transport to the hill top; the line was built in 1907 by Abdul Hussein Adamjee Peerbhoy and features over 281 curves along its route through the Western Ghats. • The railway is maintained by Central Railway under the Western Railway Zone and is a notified Heritage Site of Maharashtra; it uses small diesel-hauled coaches that can carry around 20 passengers each. • 💡 Option A (Tamil Nadu) is wrong because Tamil Nadu is home to the Nilgiri Mountain Railway, not Matheran — a common confusion in exams; Option C (West Bengal) is wrong because West Bengal hosts the Darjeeling Himalayan Railway; Option D (Himachal Pradesh) is wrong because Himachal Pradesh has the Kalka–Shimla Railway, not the Matheran line.

Correct Answer: A. BG

• **BG (Broad Gauge)** = In all official Indian Railways technical documents, locomotive plates, wagon stencils, and timetable notations, Broad Gauge is abbreviated as BG. This two-letter code is standardised across the Ministry of Railways to avoid confusion in multilingual record-keeping across 17 railway zones. • **Other gauge codes** — MG stands for Meter Gauge (1000 mm), NG stands for Narrow Gauge (762 mm or 610 mm), and SG stands for Standard Gauge (1435 mm) in Indian context — though SG is relatively rare in official documents since Standard Gauge is used only in Metro and High-Speed projects. • BG locomotives are stencilled with the code on both sides of the cab so yard staff can visually identify the gauge compatibility of rolling stock at a glance, preventing wrong-gauge shunting operations. • 💡 Option B (MG) is wrong because MG specifically denotes Meter Gauge, which has a width of 1000 mm — different from Broad Gauge; Option C (SG) is wrong because SG denotes Standard Gauge (1435 mm), not Broad Gauge; Option D (NG) is wrong because NG denotes Narrow Gauge tracks of 762 mm or 610 mm width.

Correct Answer: B. Inner rail is higher than outer

• **Inner rail is higher than outer** = Negative super-elevation (also called adverse cant) is the condition where the inner rail of a curve is raised above the outer rail — the opposite of the normal design where the outer rail is higher to counteract centrifugal force. This reversal acts against the centrifugal tendency and sharply increases the risk of the train tilting inward or overturning. • **Where it occurs** — Negative super-elevation is unavoidable at certain complex turnouts (crossovers) where one curved route transitions into a curve in the opposite direction; Indian Railways track engineers limit the maximum permissible negative super-elevation to 25 mm on BG to reduce derailment risk. • Under normal positive super-elevation, the outer rail is raised by a calculated amount (cant) so that the resultant of gravity and centrifugal force acts vertically through the track, keeping wheels firmly seated on the rail. • 💡 Option A (Train speeds up) is wrong because super-elevation of any kind affects stability, not engine power or speed — the train's speed is controlled by the traction system independently; Option C (Track is perfectly flat) is wrong because zero cant is the normal level condition, distinct from negative cant where one rail is positively raised over the other; Option D (Rails are wider) is wrong because super-elevation refers to relative height of the rails, not the distance between them.

Correct Answer: B. Meter Gauge

• **Meter Gauge (1000 mm)** = The Nilgiri Mountain Railway (NMR) in Tamil Nadu operates on a 1000 mm Meter Gauge track running 46 km from Mettupalayam to Ooty (Udhagamandalam) through the Nilgiri Hills. It is the only rack-and-pinion mountain railway in India. • **Rack-and-pinion system** — To climb the steep 1-in-12 gradient (the steepest rack section in Asia), the NMR uses the Abt rack system where a central toothed rail (rack) engages a pinion gear under the locomotive, providing traction impossible for adhesion-only railways. Maximum gradient on the rack section is 8.33%. • The NMR was inscribed as a UNESCO World Heritage Site in 2005 as part of the 'Mountain Railways of India' grouping (along with Darjeeling and Kalka–Shimla railways); it was built by the British between 1891 and 1908. • 💡 Option A (Broad Gauge) is wrong because Broad Gauge (1676 mm) is used on Indian mainline railways, not the steep Nilgiri gradients which demand the lighter, tighter Meter Gauge; Option C (Standard Gauge) is wrong because Standard Gauge (1435 mm) is used for Metro systems in India, not heritage hill railways; Option D (Narrow Gauge) is wrong because Narrow Gauge (762 mm or 610 mm) is used in Darjeeling and Matheran, not NMR, which is specifically a Meter Gauge line.

Correct Answer: B. Preventing wheel flange from climbing

• **Preventing wheel flange from climbing** = Check rails (also called guard rails) are short lengths of rail fixed parallel and close to the inner rail on sharp curves and at level crossings. They constrain the inner face of the wheel flange so that, under high lateral centrifugal force, the outer wheel cannot ride up over the rail head and cause a derailment. • **Placement detail** — Check rails are placed on the inner (low) rail side of a curve, with a clearance of 44–51 mm from the running rail on Broad Gauge. They are mandatory on curves sharper than a 600 m radius on Indian Railways and at all level crossings. • In addition to preventing flange climbing, check rails reduce gauge spread on sharp curves by opposing the lateral thrust of the wheels, protecting the fastening system of the running rail. • 💡 Option A (Beautification) is wrong because check rails are purely a functional safety component with no aesthetic purpose — they are unpainted structural steel elements; Option C (Holding ballast) is wrong because ballast is held in place by the track geometry and shoulder ballast design, not by check rails; Option D (Increasing speed) is wrong because check rails actually impose a speed restriction on the curve segment by guiding wheels safely through tight geometry.

Correct Answer: A. Maintaining track gauge

• **Maintaining track gauge** = Sleepers (also called cross-ties or railway ties) are laid perpendicular to the rails and hold them at the precise gauge distance — 1676 mm for Broad Gauge. They are the primary structural element that prevents the rails from spreading apart under the lateral thrust of wheel flanges. • **Additional functions** — Beyond gauge maintenance, sleepers transfer the vertical load from rails to the ballast bed, absorb and dampen vibration and shock from passing trains, and provide the elastic fixing point for rail fasteners (spikes, clips, or screws). In India, pre-stressed concrete (PSC) sleepers have largely replaced wooden ones since the 1970s for longer service life. • Indian Railways specifies 1540 sleepers per kilometre of track on high-speed routes to ensure adequate load distribution; on loops and sidings, the density is lower. The standard PSC sleeper weighs about 268–290 kg. • 💡 Option B (Providing electricity) is wrong because sleepers are mechanical structural elements — electricity for signalling is carried through separate insulated track circuits, not through sleepers; Option C (Decorating the track) is wrong because sleepers are engineering components designed for structural performance, not appearance; Option D (Reducing train weight) is wrong because sleepers are fixed ground infrastructure and have no effect on the weight of the rolling stock above them.