Question 1

In Indian state public works departments (PWD), who is considered the technical head of the department at the state level?

Accepted Answer

Introduction / Context: Public Works Departments (PWD) in Indian states are large technical organizations responsible for planning, designing, constructing, and maintaining public infrastructure such as roads, bridges, and buildings. Understanding the administrative versus technical hierarchy helps aspirants correctly identify roles and responsibilities in government engineering services. Given Data / Assumptions: The question refers to the head of the PWD within a state. “Head” here is interpreted as the top technical authority within the engineering cadre, not the political or administrative head. Common PWD hierarchy includes: Chief Engineer (or Engineer-in-Chief), Superintending Engineer, Executive Engineer, etc. Concept / Approach: Indian PWDs have dual leadership: a political head (Minister) and an administrative head (Secretary/Principal Secretary). The senior-most engineering post is the Chief Engineer (often designated Engineer-in-Chief in some states). Exam questions typically treat the Chief Engineer as the “head” in the technical sense. Step-by-Step Solution: Identify whether the head sought is political or technical → technical head is intended in engineering exam context.Compare roles: Minister gives policy direction; Secretary manages administration; Chief Engineer leads technical decisions and engineering staff.Therefore, select “Chief Engineer.” Verification / Alternative check: State PWD organization charts consistently place the Chief Engineer/Engineer-in-Chief at the apex of the engineering hierarchy, overseeing Superintending and Executive Engineers. Why Other Options Are Wrong: Transport Minister is a political executive, not the engineering head. Superintending Engineer and Executive Engineer are subordinate technical posts. Common Pitfalls: Confusing political/administrative heads with the technical head; overlooking that design and execution authority rests with the Chief Engineer’s office. Final Answer: Chief Engineer

Question 2

For a concrete highway pavement with temperature/steel reinforcement, what depth below the top surface is reinforcement generally placed to control temperature and shrinkage stresses?

Accepted Answer

Introduction / Context: Reinforcement in cement concrete pavements is provided primarily to control temperature and shrinkage cracking. Its vertical position (cover from the top surface) significantly influences crack control and durability under traffic and environmental actions. Given Data / Assumptions: Rigid pavement (concrete road slab) with temperature steel. Typical practice under Indian/standard highway guidelines. Focus on the usual nominal depth below the top surface. Concept / Approach: To effectively control surface-origin cracks due to thermal gradients and drying shrinkage, reinforcement is placed relatively near the surface. Too deep a placement reduces its crack-arresting efficiency; too shallow a placement risks corrosion and damage during construction and service. Step-by-Step Solution: Recognize that temperature cracks initiate near the top surface because of cooling and shrinkage.Place reinforcement close enough to intercept microcracks and distribute stresses.Standard practice keeps steel about 5 cm below the surface, providing both effectiveness and adequate cover. Verification / Alternative check: Design guides commonly specify cover values around 50 mm for pavements, balancing durability and crack control. Field experience corroborates satisfactory performance with ~5 cm placement. Why Other Options Are Wrong: 6–9 cm lowers the steel, diminishing crack control for top-surface thermal stresses; 5 cm remains the accepted, effective compromise. Common Pitfalls: Confusing slab “mid-depth” reinforcement (used for other structural members) with pavement practice; ignoring the need for corrosion cover in deicing or coastal environments. Final Answer: 5 cm

Question 3

Traffic growth for highway design: If the last traffic census recorded P vehicles per day, the annual growth rate is r (fraction per year), and n years have elapsed since the last count, what is the design traffic A (vehicles/day)?

Accepted Answer

Introduction / Context: Forecasting design traffic is a key step in pavement and geometric design. A common method assumes compound annual growth from a base traffic count to estimate the current or design-year average daily traffic. Given Data / Assumptions: Base count P = vehicles/day at last census. Annual growth rate r (e.g., 0.06 for 6%). Elapsed time n years since the census. Uniform compound growth, no disruptive step changes. Concept / Approach: Compound growth increases traffic multiplicatively each year. Therefore, future traffic equals the base multiplied by the compounding factor repeated n times. Step-by-Step Solution: Annual factor = (1 + r).After n years: A = P * (1 + r)^n.Choose the option that matches this formula exactly. Verification / Alternative check: For small r, a linear approximation P(1 + n r) is sometimes used for quick checks; however, design uses the compound expression. Why Other Options Are Wrong: (b) implies decline; (c) and (d) are nonstandard exponents unrelated to elapsed years. Common Pitfalls: Using percentage (e.g., 6) instead of fraction (0.06) in (1 + r); ignoring compounding for multi-year projections. Final Answer: P (1 + r)^n

Question 4

For a lemniscate curve used as a transition throughout (total deflection angle = Δ), what is the maximum polar angle (measured from the initial tangent)?

Accepted Answer

Introduction / Context: Lemniscate curves (commonly Bernoulli lemniscates) are used in highway geometric design to provide a continuously varying curvature suitable for higher-speed transition, especially where a large total deflection must be negotiated smoothly. Given Data / Assumptions: The total deflection through the lemniscate is Δ. The curve is transitional throughout (curvature varies from zero at the tangent to a maximum and returns appropriately). We seek the maximum polar angle from the tangent. Concept / Approach: For a lemniscate used as a fully transitional element (symmetric about the point of maximum offset/curvature), the polar angle at the point of symmetry is half of the total deflection. Thus, the “maximum” polar angle equals Δ/2. Step-by-Step Solution: Interpret Δ as the full change of direction covered by the transitional curve.For a symmetric transitional curve, the midpoint (maximum polar angle) occurs at half the total change.Hence, maximum polar angle = Δ / 2. Verification / Alternative check: Graphical construction of the lemniscate (equal areas/angles on either side) confirms symmetry and the Δ/2 result at the apex. Why Other Options Are Wrong: Δ/3, Δ/4, Δ/5, and Δ/6 underestimate the apex location, contradicting the inherent symmetry of a transitional lemniscate. Common Pitfalls: Confusing lemniscate properties with those of clothoids or simple circular transitions; misreading Δ as half the deflection rather than total. Final Answer: Δ/2

Question 5

In hill-road cross-drainage and surface drainage practice, are pavements generally provided with a two-sided camber? Choose the statement that best reflects common practice.

Accepted Answer

Introduction / Context: Camber is the two-sided cross slope often used on level terrain to shed water to both sides. Hill roads, however, have distinct drainage needs because of steep hillside and valley sides, catch-water drains, and frequent super-elevation on curves. Given Data / Assumptions: Typical two-lane hill road with an uphill (hillside) and a downhill (valley) edge. Surface water needs to be intercepted efficiently to protect the pavement and slopes. Superelevation on horizontal curves is designed independently of camber. Concept / Approach: On hill roads, a single cross-fall toward the hillside or toward adequate drainage facilities is commonly adopted rather than a traditional two-sided camber. Camber is “seldom” provided because the terrain naturally dictates a one-way slope and the use of catch-water drains on the uphill side and side drains on the valley side. Step-by-Step Solution: Identify drainage objective: move water off the carriageway quickly and safely.Apply hill-road practice: one-way cross slope and catch-water drains, with super-elevation where curves require it.Therefore, “Hill roads are seldom provided a camber.” Verification / Alternative check: Standard hill-road guidelines emphasize one-way cross slope and cut-off drains; camber is not a typical default on such sections. Why Other Options Are Wrong: Options (a) and (b) incorrectly associate camber with specific curve types; super-elevation, not camber, governs on curves. (d) is incorrect because (c) reflects the accepted practice. Common Pitfalls: Equating camber with any cross-fall; misapplying plain-terrain principles to mountainous terrain. Final Answer: Hill roads are seldom provided a camber

Question 6

In the geometric design of traffic rotaries (roundabouts), the width of the circulating carriageway (rotary) should be taken as which of the following practical rules of thumb?

Accepted Answer

Introduction / Context: Roundabout (rotary) design requires adequate circulating width to accommodate entering streams, weaving, and lane changes. A common sizing cue links the circulating width to the largest approach width with a margin to allow safe weaving. Given Data / Assumptions: Multiple approach roads with varying widths. Design aims for safe weaving and capacity with conventional passenger traffic mix. No channelization beyond standard splitter islands. Concept / Approach: A pragmatic approach is to provide a circulating width at least equal to the widest approach plus one extra lane for weaving and storage. This aligns with typical roundabout design guidance that scales circulating width to entry width and expected weaving volumes. Step-by-Step Solution: Identify the widest approach road carriageway.Add one lane width to accommodate weaving/storage demands.Adopt that sum as the circulating carriageway width (subject to detailed capacity checks). Verification / Alternative check: Detailed weaving-section analysis (weaving width and length) refined by expected flows will confirm or adjust this initial sizing. Why Other Options Are Wrong: (a) and (d) are arbitrary; (b) underestimates weaving needs and can cause conflicts. Common Pitfalls: Ignoring the weaving requirement; making the rotary too narrow, which elevates crash risk and reduces capacity. Final Answer: Equal to the width of the widest road plus one additional traffic lane

Question 7

On hill roads where several hairpin bends are necessary, what minimum intervening distance between successive hairpin bends is generally maintained to ensure safety and stability?

Accepted Answer

Introduction / Context: Hairpin bends (switchbacks) are sharp 180-degree turns used to rapidly gain elevation on steep terrain. Spacing these bends properly is essential for safety, sight distance, vehicle maneuverability, and slope stability. Given Data / Assumptions: Standard two-lane hill road geometry. Typical design vehicles include buses and medium trucks. Terrain and right-of-way permit recommended spacing. Concept / Approach: Providing a minimum intervening distance helps in accommodating transition lengths, superelevation runoff, driver comfort, and drainage works between curves. A commonly adopted minimum is about 60 m under Indian hill-road practice. Step-by-Step Solution: Assess required space for curve transition and super-elevation development.Ensure adequate sight distance and room for protective works (retaining, breast walls, drains).Adopt 60 m as the minimum safe intervening distance between hairpins where feasible. Verification / Alternative check: Where terrain allows, larger spacing (e.g., 100 m) may be used for improved comfort; however, 60 m is widely accepted as the lower bound. Why Other Options Are Wrong: 20–40 m are too short for safe transitions and sight distance; 100 m, while safe, is not the typical minimum and may be impractical in steep terrain. Common Pitfalls: Placing bends too close due to right-of-way constraints; neglecting super-elevation runoff length between successive hairpins. Final Answer: 60 m

Question 8

Historic road construction principle: Who stated that stone size used in a road should not exceed about 2.5 cm in any dimension because the wheel contact length on a smooth level surface is roughly 2.5 cm, and larger stones are “mischievous” for the…

Accepted Answer

Introduction / Context: Classical road builders proposed distinct philosophies for pavement layers and stone size. Understanding who advocated which principle helps in remembering construction methods like Telford’s large hand-packed stones vs. Macadam’s small broken-stone surface. Given Data / Assumptions: Quotation emphasizes limiting stone size to about 2.5 cm (1 inch). Focus is on the wearing surface and wheel contact characteristics. Historical figures: Telford, Macadam, Tresaguet, Sully. Concept / Approach: John Loudon McAdam revolutionized road building by insisting on well-graded, small broken stones, compacted to form an impermeable, stable surface. He explicitly argued against large stones on the running surface, declaring them harmful (“mischievous”). Step-by-Step Solution: Identify which engineer advocated small broken stones: Macadam.Recall Telford preferred a foundation of large stones, but not as the wearing course.Therefore, the quotation aligns with Macadam’s doctrine. Verification / Alternative check: Historic literature on “macadamized” roads cites the 1-inch (≈2.5 cm) maximum size for surface stones to ensure tight interlock and fine running quality. Why Other Options Are Wrong: Telford and Tresaguet used larger foundation stones; Sully is not associated with this specific principle. Common Pitfalls: Assuming all pioneers endorsed the same stone sizes; mixing up foundation versus wearing course specifications. Final Answer: Macadam

Question 9

Highway design basis: Modern highway geometric and pavement design considers multiple vehicle-related parameters. Which of the following set best represents the core vehicle parameters used (in combination with traffic and environmental inputs)?

Accepted Answer

Introduction / Context: Highway design does not rely on a single vehicle parameter. Instead, it integrates several vehicle characteristics with traffic, climate, and subgrade inputs to arrive at safe and durable geometric and pavement designs. Recognizing these parameters helps explain why standards specify lane widths, turning radii, load repetitions, and pavement layer thicknesses. Given Data / Assumptions: The options list major vehicle-related parameters relevant to design. Question asks which are used for design (not which one parameter dominates). Applies to both geometric elements (e.g., curves, intersections) and pavement thickness design. Concept / Approach: Pavement thickness is mainly governed by axle loads (magnitude), axle configurations/spacing (load repetitions and damage), and traffic spectra. Geometric design (turning, layout, clearances) depends on wheelbase, track width, and overall length. Therefore, all listed parameters contribute to some aspect of design. Step-by-Step Solution: Identify pavement-critical parameters → axle loads and axle spacing (load interaction and damage).Identify geometry-critical parameters → wheelbase and overall length (turning paths, swept path).Conclude multiple parameters are concurrently used → select the comprehensive option. Verification / Alternative check: Standard design guides compile vehicle design templates (overall length and wheelbase) for intersections and curves, and axle loading spectra for mechanistic-empirical pavement design—confirming the multi-parameter basis. Why Other Options Are Wrong: Axle loads only: ignores geometry and load spacing effects. Axle spacing only: does not capture magnitude or geometry. Wheelbase or overall length alone: cover turning geometry but not structural design. Common Pitfalls: Assuming one parameter (e.g., axle load) governs all aspects; geometry still needs length and wheelbase. Final Answer: All the above.

Question 10

Night visibility and valley-curve design checks: Select the correct statements used in headlight-sight-distance considerations for valley curves on highways.

Accepted Answer

Introduction / Context: At night, the safety on valley curves is checked using the headlight sight distance concept. The geometry must ensure that the illuminated beam can reveal an obstacle in time for a driver to react and stop. This check uses standardized assumptions about headlight mounting height, beam angle, and object height. Given Data / Assumptions: Headlight height above road surface ≈ 0.75 m. Beam angle ≈ 1 degree above the grade line. Object height for nighttime visibility on valley curves ≈ 0 m (lying object). Concept / Approach: In a valley curve, the vehicle dips; the headlight beam may overshoot if the curve is too sharp. Using a standard headlight height and small upward beam angle, the length of curve must be sufficient so the beam hits the road surface far enough ahead to provide the required stopping sight distance. Assuming object height zero is conservative for safety. Step-by-Step Solution: Adopt headlight height H = 0.75 m.Adopt upward beam angle α ≈ 1°.Assume object height = 0 m on the pavement.Check valley curve length so illuminated point ≥ required stopping sight distance. Verification / Alternative check: These assumptions are widely used in highway design manuals to simplify a complex light-geometry problem while maintaining conservative safety margins. Why Other Options Are Wrong: Any single statement alone is incomplete; all three together describe the standard headlight criterion. “None of these” contradicts established practice. Common Pitfalls: Using object height 0.15 m (daytime summit-curve check) instead of 0 m for valley curves at night. Final Answer: All the above.

Question 11

Transport modes in India: Which of the following systems is not used for the conveyance of passengers in India?

Accepted Answer

Introduction / Context: India employs multiple transport modes for passenger movement: railways, roads, civil aviation, and coastal/inland waterways (shipping). Understanding what counts as a passenger mode clarifies planning priorities and infrastructure investments. Given Data / Assumptions: We are concerned with systems carrying passengers in routine public service. Pipelines primarily carry fluids and gases. Shipping includes ferries and cruise/liner services for people. Concept / Approach: Passenger transport modes must support boarding, seating, tickets, and safety systems for people. Railways, roads (buses, taxis), shipping (ferries), and airlines obviously satisfy this. Pipelines are engineered for commodities (petroleum, gas, water, slurry) and do not carry passengers. Step-by-Step Reasoning: List recognized passenger modes → rail, road, air, water.Identify pipeline purpose → commodity conveyance only.Select “Pipe lines” as not used for passengers. Verification / Alternative check: National transport statistics and policy documents classify pipelines strictly as freight/utility networks, not passenger systems. Why Other Options Are Wrong: Railways, roads, shipping, airlines: core passenger modes with established public services across India. Common Pitfalls: Assuming “shipping” is freight-only; India operates passenger ferries in several states. Final Answer: Pipe lines.

Question 12

Rigid pavement analysis: For the design of cement concrete pavement under corner loading, which formula does the Indian practice (IRC) recommend?

Accepted Answer

Introduction / Context: Cement concrete (rigid) pavements are analyzed for critical load positions: interior, edge, and corner. Corner loading is particularly severe because slab support is limited, leading to higher tensile stresses at the top or bottom fibers depending on conditions. Given Data / Assumptions: Rigid slab resting on subgrade idealized as a dense liquid or Winkler foundation. Corner load case considered critical for design. Standard Indian practice references classical analytical solutions. Concept / Approach: Westergaard’s theory provides closed-form stress solutions for different load positions accounting for slab dimensions, load radius of contact, modulus of subgrade reaction, and slab stiffness. For corner loads, the stress expression allows designers to check slab thickness and joint layout to prevent cracking. Step-by-Step Solution: Idealize slab–subgrade system and identify load position (corner).Apply Westergaard corner-stress formula with appropriate radius of relative stiffness and load contact area.Verify tensile stress ≤ allowable flexural strength → select slab thickness. Verification / Alternative check: Modern mechanistic–empirical methods still rely on Westergaard principles for baseline checks, corroborating its continued relevance in design manuals. Why Other Options Are Wrong: Kelly, Goldbeck, Spanlar, Picker: not the standard corner-load reference in IRC-based rigid pavement design. Common Pitfalls: Using interior-load formulas for corner cases, underestimating tensile stress. Final Answer: Westergaard's formula.

Question 13

Moisture cut-off in embankment sections: When the subgrade is about 0.6–1.0 m above the water table (embankment), what thickness of a coarse sand cut-off layer is typically provided to prevent upward moisture movement?

Accepted Answer

Introduction / Context: Moisture ingress from a nearby water table can weaken subgrades, reduce bearing capacity, and accelerate pavement deterioration. In embankment situations where the subgrade is moderately above the water table, a thin capillary cut-off of coarse sand is commonly provided to interrupt capillary rise. Given Data / Assumptions: Water table lies roughly 0.6–1.0 m below subgrade level (embankment condition). Capillary rise through fine soils can reach the pavement unless interrupted. Coarse sand has low capillarity; a thin layer can act as a capillary break. Concept / Approach: The objective is to create a drainage/cut-off interface that prevents moisture migration to the upper layers. For moderate separations from the water table, a 15 cm coarse-sand blanket is usually adequate as a practical and economical capillary break. Step-by-Step Solution: Assess risk of capillary rise given water table distance.Select a non-capillary medium (coarse sand) to disrupt upward suction.Adopt standard practical minimum thickness → 15 cm. Verification / Alternative check: For more severe conditions (water table near subgrade or highly fine soils), thicker blankets or additional drainage layers may be specified, but 15 cm is a common baseline for the stated condition. Why Other Options Are Wrong: 20–45 cm: used in more severe capillarity or perched water problems; not the typical minimum for the given range. “None of these” contradicts standard practice. Common Pitfalls: Relying on coarse sand without providing outlets for intercepted moisture. Final Answer: 15 cm.

Question 14

Traffic operations: The distance a vehicle travels during the driver’s perception and brake-reaction time is known as what?

Accepted Answer

Introduction / Context: Stopping sight distance (SSD) is the sum of two components: the distance covered during the driver’s perception–reaction time and the distance required to actually brake to a stop. Distinguishing these components helps in setting safe sight distances and sign placement. Given Data / Assumptions: Driver perceives a hazard and reacts (moves foot to brake) over a standard reaction time. Vehicle is initially at design speed. No grade adjustments are considered in the definition itself. Concept / Approach: The distance traveled during perception and reaction—before effective braking starts—is called the lag distance. After this, the braking distance is added to get SSD. Mislabeling these can lead to under-designed sight distances. Step-by-Step Solution: SSD = lag distance + braking distance.Lag distance depends on speed and reaction time (typically 2.5 seconds in many manuals).Identify the asked component → distance during perception–reaction → lag distance. Verification / Alternative check: Design manuals consistently define lag distance as the perception–reaction component of SSD. Braking distance is computed separately using deceleration assumptions. Why Other Options Are Wrong: Sight distance/Stopping distance: broader measures that include or exceed lag distance. Headway distance: spacing between vehicles, unrelated to perception–reaction distance definition. Common Pitfalls: Confusing lag distance with total SSD, leading to insufficient sight lines. Final Answer: Lag distance.

Question 15

Camber shape effect: On a pavement with a parabolic camber, how does the angle of inclination (cross slope) of vehicles vary from the crown to the edges?

Accepted Answer

Introduction / Context: Camber (cross fall) shapes the transverse slope of a road to drain water. A popular shape is a true (quadratic) parabolic camber, which avoids abrupt slope changes and improves riding comfort compared to a straight-line (plane) camber. Given Data / Assumptions: Parabolic camber profile across the carriageway. Angle of inclination refers to the local cross slope at a given offset from the crown. Concept / Approach: In a parabolic camber, the slope is zero at the crown and increases with distance from the centerline, reaching its maximum at the pavement edges. This yields gentle near-crown slopes to enhance comfort and larger edge slopes to provide drainage capacity. Step-by-Step Reasoning: Parabolic profile y = kx^2 (measured from crown).Local slope dy/dx = 2kx → increases linearly with x.Hence, slope is smallest near crown and largest at edges → vehicles are more inclined at edges. Verification / Alternative check: Camber tables show edge slopes equal to the specified camber percentage, while slope at the crown is effectively zero for a parabolic form. Why Other Options Are Wrong: “More at the crown” or “Less at the edges” contradict the mathematics of a parabola. “Same at edges and crown” applies to plane camber, not parabolic. Common Pitfalls: Assuming a uniform cross slope for all camber shapes; only straight-line camber has constant slope. Final Answer: More at the edges.

Question 16

Definition check (degree of curve): In highway engineering, the degree of a road curve is defined as the central angle (in degrees) subtended by an arc length of how many metres?

Accepted Answer

Introduction / Context: The “degree of curve” is a convenient way to express curvature without directly quoting the radius. Indian highway practice defines degree of curve with a fixed arc length so that designers and surveyors can translate between degree and radius easily. Given Data / Assumptions: Highway (not railway) convention. Degree is the central angle for a specified arc length. We must choose the correct reference arc length. Concept / Approach: For roads, the degree of curve is based on an arc length of 30 metres. Therefore, if D is the degree of curve, the radius can be computed by R = 30 * 180 / (π * D) ≈ 1718.9 / D (metres). This linkage supports quick conversion between geometry set-out (by degrees) and design radius. Step-by-Step Reasoning: Recall definition → angle subtended by a 30 m arc.Recognize derived relation R ≈ 1718.9 / D.Select the corresponding arc length value from options → 30 metres. Verification / Alternative check: Survey and geometric design texts for roads consistently adopt the 30 m arc definition; railways commonly use a chord-based 30 m definition in some contexts, but for highway curves, the 30 m arc is the standard reference. Why Other Options Are Wrong: 10, 20, 25, 50 m: not the standard arc length used to define road curve degree in highway design. Common Pitfalls: Confusing arc-based road definition with chord-based railway definitions. Final Answer: 30 metres.

Question 17

Condition for “no super-elevation” provision: A circular curve of radius R = 1400 m carries traffic at 80 km/h. If the practice is to omit super-elevation when camber alone is adequate, what camber (%) would satisfy this condition?

Accepted Answer

Introduction / Context: Super-elevation (e) and side friction (f) together balance the lateral acceleration on curves according to the relation e + f = V^2 / (225 R) when V is in km/h and R in metres. For gentle curves, practice sometimes omits super-elevation if the normal camber provides sufficient cross fall to meet the equilibrium condition comfortably. Given Data / Assumptions: Design speed V = 80 km/h. Curve radius R = 1400 m. No super-elevation provided → e = 0; camber provides the cross slope. Check uses the equilibrium equality for threshold. Concept / Approach: Set e = 0 and compute the equilibrium value V^2 / (225 R). If the available camber equals or exceeds this value, super-elevation may be omitted. Typical bituminous road cambers are around 2% on straights, which may be adequate for very large-radius curves at moderate speeds. Step-by-Step Solution: Compute V^2 = 80^2 = 6400.Compute denominator = 225 * 1400 = 315000.Evaluate V^2 / (225 R) = 6400 / 315000 ≈ 0.02032 → 2.032%.For “no super-elevation,” select camber ≈ 2% (closest listed value). Verification / Alternative check: With camber 2%, the small remaining demand is within practical tolerance, especially considering conservative rounding and operational variability. Why Other Options Are Wrong: 4%, 3%: Higher than necessary; super-elevation would certainly not be required, but these exceed typical straight-road cambers. 1.7% or 1%: Too small; would not satisfy the equilibrium threshold (~2.03%). Common Pitfalls: Using the constant 127 from railway formulas; highway practice with friction uses 225 for km/h and metres. Final Answer: 2%.

Question 18

Highway design – superelevation formula If V is the design speed in km/h and R is the radius of a horizontal circular curve in metres, the required superelevation e (as a fraction) is given by which expression?

Accepted Answer

Introduction / Context: Superelevation is the transverse upward tilt of the pavement on horizontal curves to counteract the lateral acceleration experienced by vehicles. In highway engineering, it is expressed as a fraction e (rise per unit width) related to speed and curvature. Choosing the correct formula is essential for comfort and safety. Given Data / Assumptions: V = design speed in km/h. R = radius of the horizontal curve in metres. Standard highway relationship that neglects lateral friction at the chosen design speed (all centripetal demand provided by superelevation). Concept / Approach: For equilibrium on a banked curve, the required centripetal acceleration V^2/(225R) (with V in km/h) is balanced by the component of gravity along the road surface. This yields e = V^2/(225R) when lateral friction is not relied upon at the design speed. When friction is also considered, the combined relation becomes e + f = V^2/(127R), where f is the side-friction factor. Step-by-Step Solution: Start from equilibrium: e = (v^2)/(gR) in consistent units.Convert v from km/h to m/s and simplify constants to obtain 225 in the denominator.Therefore, with no reliance on side friction at design speed, e = V^2 / (225 * R). Verification / Alternative check: Compare with the combined design relation e + f = V^2/(127R). Setting f = 0 for the design (conservative) case gives e = V^2/(127R). But standard IRC-type practice commonly uses e = V^2/(225R) for the equilibrium-only expression and keeps a separate check with friction for higher speeds. Why Other Options Are Wrong: Options C and D invert the relationship. Option B corresponds to the combined e + f form. Option E has incorrect dimensions. Common Pitfalls: Mixing the two constants 127 and 225; using metres per second for V without unit conversion; exceeding maximum permissible e in practice (typically capped). Final Answer: e = V^2 / (225 * R)

Question 19

Flexible pavement – recommended sub-base thickness for a poorly graded subgrade soil For a poorly graded (weak) subgrade soil under ordinary traffic, which thickness of sub-base is commonly provided?

Accepted Answer

Introduction / Context: The sub-base layer distributes wheel loads and protects the underlying subgrade. When the subgrade is poorly graded or weak, designers increase the sub-base thickness to improve support and durability. Given Data / Assumptions: Poorly graded subgrade indicating low bearing capacity. Ordinary rural/urban highway traffic (not expressway level). Standard granular sub-base material. Concept / Approach: Empirical catalogues and experience suggest thicker sub-bases for weaker subgrades to limit stress and rutting. A thickness around 25 cm is a common baseline for such conditions; lighter subgrades may require more, while strong subgrades may allow less. Step-by-Step Solution: Identify subgrade condition → poorly graded/weak.Consult typical design tables → increased sub-base thickness recommended.Select practical standard thickness → 25 cm among the given choices. Verification / Alternative check: Checks using CBR-based design charts typically map low CBR (poor subgrade) to higher granular thicknesses near 0.25 m or more for conventional traffic categories. Why Other Options Are Wrong: 10–20 cm are often inadequate on weak subgrades; 30 cm can be used for heavier traffic but is beyond a common baseline. Common Pitfalls: Ignoring drainage and frost; not compacting to target density; skipping a filter/separator geotextile where fines pumping is expected. Final Answer: 25 cm

Question 20

Road markings – meaning of broken white longitudinal lines What is the correct interpretation of broken (discontinuous) white longitudinal pavement lines for drivers?

Accepted Answer

Introduction / Context: Pavement markings communicate lane usage and overtaking permissions. Broken white longitudinal lines are among the most common road markings and must be understood for safe operations. Given Data / Assumptions: Broken (dashed) white line separating same-direction lanes or guiding a single carriageway. Normal daylight and visibility conditions; other signs and markings may also apply. Concept / Approach: Broken white lines indicate that lane changing or overtaking is allowed when safe, after adequate observation and signaling. In contrast, continuous lines typically prohibit crossing. Step-by-Step Solution: Interpret marking type: broken white → permissive.Evaluate safety: check mirrors, blind spots, opposing/adjacent traffic.Execute maneuver only if adequate sight distance and gaps exist. Verification / Alternative check: Traffic control manuals uniformly classify broken white lines as permissive lane lines; solid lines are restrictive or warning-based. Why Other Options Are Wrong: Option A is incomplete (does not specify permissive crossing). Option B contradicts standard meaning. Option D cannot be true since B is incorrect. Option E is inapplicable. Common Pitfalls: Crossing near intersections or pedestrian crossings without extra caution; ignoring additional signs that might temporarily restrict overtaking. Final Answer: They may be crossed over at the driver’s discretion when safe

Highway Engineering Questions