Question 1

Weep holes in retaining and breast walls Typical spacing of weep holes provided to relieve hydrostatic pressure behind retaining/breast walls is:

Accepted Answer

Introduction / Context: Weep holes allow trapped water behind retaining and breast walls to escape, reducing pore water pressure and preventing uplift or sliding. Proper spacing ensures adequate drainage and durability. Given Data / Assumptions: Masonry or reinforced concrete retaining/breast wall on granular backfill. Standard small-diameter weep holes (e.g., 75–100 mm). Moderate rainfall and drainage blanket assumed. Concept / Approach: Practical guidance often calls for approximately 1 m × 1 m spacing as a baseline, adjustable with wall height, backfill permeability, and presence of drainage layers or filter media. Step-by-Step Solution: Select baseline spacing that balances drainage and constructability.Adopt 100 cm vertically and 100 cm horizontally c/c for typical cases.Place weep holes with proper filter to prevent soil piping. Verification / Alternative check: Site-specific designs refine spacing based on hydrogeology and wall height; however, 1 m × 1 m is a common rule-of-thumb in many standard drawings. Why Other Options Are Wrong: 50 cm × 50 cm is often unnecessary; 100 × 120 or 120 × 100 are asymmetric and may under-drain in one direction unless justified. Common Pitfalls: Omitting filters; placing holes too high; failing to provide a drainage layer behind the wall. Final Answer: 100 cm vertically and 100 cm centre-to-centre horizontally

Question 2

In highway vehicle dynamics, which type of resistance is generally considered negligible for a properly designed road vehicle under normal operating conditions?

Accepted Answer

Introduction / Context: When estimating tractive effort and power needs for road vehicles, engineers account for several resistances: rolling, aerodynamic (wind), grade (due to slope), acceleration, and minor mechanical losses. Understanding which components materially affect performance helps in quick, safe preliminary design calculations. Given Data / Assumptions: Vehicle is in good mechanical condition with properly lubricated bearings. Operation is at normal highway speeds on typical pavements. No extreme winds or steep grades are assumed unless stated. Concept / Approach: Total tractive resistance is commonly approximated as the sum of rolling resistance, aerodynamic drag, grade resistance, and small mechanical losses. Of these, rolling resistance and aerodynamic drag dominate at moderate and high speeds, and grade resistance dominates on slopes. Bearing or axle resistance is typically very small compared with the others and is often absorbed into rolling resistance or neglected outright in simplified models. Step-by-Step Solution: Identify principal resistances: rolling, wind, grade, and minor mechanical (axle).Compare magnitudes: axle losses are orders of magnitude smaller than rolling and wind terms for well-maintained vehicles.For preliminary design, axle resistance is commonly ignored to simplify calculations. Verification / Alternative check: Textbook tractive effort formulas usually include rolling resistance coefficient, aerodynamic drag term proportional to v^2, and grade term W * sin(theta), with no explicit axle term, confirming it is negligible or absorbed in rolling resistance. Why Other Options Are Wrong: Rolling resistance: always present from tyre deformation and pavement texture. Wind resistance: material at moderate to high speeds; grows with speed squared. Grade resistance: significant even on mild slopes due to vehicle weight component. None of these: incorrect because axle resistance is the one usually neglected. Common Pitfalls: Double-counting axle losses and rolling resistance. Ignoring aerodynamic drag at highway speeds. Final Answer: Axle (bearing) resistance

Question 3

At a standard at-grade junction, the number of severe crossing conflict points becomes 16 when the intersecting roads are:

Accepted Answer

Introduction / Context: Traffic conflicts are interactions between vehicles that can lead to crashes. At unchannelized right-angle intersections, the count of crossing, merging, and diverging conflicts depends on the directionality (one-way or two-way) of the approaches. Given Data / Assumptions: Unsignalized, unchannelized at-grade four-leg intersection. Geometric approaches have no dedicated turning lanes or medians. “Severe” conflicts refer to crossing conflicts. Concept / Approach: Two-way movements on both intersecting roads create the maximum permutations of through and turning paths that cross each other, thus maximizing the number of crossing conflict points compared to combinations that include one-way approaches. Step-by-Step Solution: Enumerate through and turning movements for each approach in two-way–two-way condition.Count unique crossing paths where two vehicle trajectories intersect at-grade.This standard configuration yields 16 crossing conflict points. Verification / Alternative check: Conflict point diagrams in traffic engineering texts show 16 crossing conflicts for two-way–two-way intersections, fewer when any approach is one-way because several opposing movements are eliminated. Why Other Options Are Wrong: Both one-way or mixed one-way/two-way: fewer opposing flows, hence fewer crossing conflicts. “None of these”: incorrect because the two-way–two-way case does have 16 crossing conflicts. Common Pitfalls: Confusing total conflicts (crossing + merging + diverging) with crossing only. Assuming channelization does not change conflict structure; it does. Final Answer: Both two-way roads

Question 4

If the degree of a road curve is defined using a standard arc length of 30 m, what is the radius of a 1° curve?

Accepted Answer

Introduction / Context: The degree of curve provides a convenient measure of curvature used in highway and railway alignment. Two common definitions are the arc definition and the chord definition. Here, the arc definition with a 30 m standard arc length is specified. Given Data / Assumptions: Arc definition of degree of curve. Standard arc length = 30 m. Degree D = 1° (central angle subtended by the 30 m arc). Concept / Approach: For the arc definition, the relation between radius R and degree D (in degrees) for an arc length s is s = (π/180) * R * D. Solving for R with s = 30 m and D = 1° gives the desired radius. Step-by-Step Solution: s = (π/180) * R * D30 = (π/180) * R * 1R = 30 * 180 / πR ≈ 5400 / 3.1416 ≈ 1718.9 m ≈ 1719 m Verification / Alternative check: Rule of thumb for arc definition with 30 m arc: R ≈ 1720 / D (with R in metres, D in degrees). For D = 1°, R ≈ 1720 m, consistent with 1719 m when calculated precisely. Why Other Options Are Wrong: 1146, 1046, 1619, 1573 m: do not satisfy the arc-length relation for D = 1° with s = 30 m; they correspond to other D values or alternate definitions. Common Pitfalls: Using the chord definition formula instead of arc definition. Mixing units (degrees vs radians) when computing. Final Answer: 1719 m

Question 5

In parking lot layout, customers generally prefer stall orientation at which angle to the aisle (consider ease of use and familiarity in public car parks)?

Accepted Answer

Introduction / Context: Stall orientation affects driver comfort, maneuvering effort, capacity, and circulation. While operators may optimize for capacity and flow, customer preference often reflects familiarity and straightforward approach geometry. Given Data / Assumptions: Public parking with mixed-skill drivers. Typical bay widths and aisle widths provided per local standards. Two-way aisles are common with 90° layouts. Concept / Approach: Perception of ease by customers is influenced by simple alignment (head-in parking), predictable reversing, and finding spaces without specialized one-way circulation. Perpendicular (90°) parking is ubiquitous in many public facilities, making it the most familiar and often preferred by casual users despite somewhat higher turning effort than shallow-angle stalls. Step-by-Step Solution: Compare turning paths: angled stalls (60°–75°) reduce steering angle but require one-way aisles and wayfinding discipline.90° stalls allow access from either direction in two-way aisles, simplifying wayfinding.Users often perceive 90° parking as straightforward and familiar, hence “preferred.” Verification / Alternative check: Many municipal lots and retail centers adopt 90° stalls for general customer use. Although angled parking can ease entry/exit, its operational constraints (one-way aisles) can confuse users, especially in constrained sites. Why Other Options Are Wrong: 60°–85°: operationally efficient in some layouts but not as universally familiar to the public. 75°: a compromise option but still typically requires one-way circulation and is less common in general-purpose facilities. Common Pitfalls: Equating operator preference (capacity, aisle flow) with user preference. Ignoring the impact of signing and one-way patterns on user comfort. Final Answer: 90° to aisles

Question 6

For a lemniscate transition used in highway geometry, if the maximum polar angle is α and the matched circle radius is R at the junction, the maximum radial distance along the lemniscate is:

Accepted Answer

Introduction / Context: Lemniscate curves are sometimes used as transition elements where curvature needs to vary in a prescribed manner. Unlike a simple clothoid, a lemniscate can provide specific curvature properties over larger deflection angles. Understanding the relationship between polar angle and radial distance helps in geometric checks and staking out the curve in the field. Given Data / Assumptions: A lemniscate transition is adopted with maximum polar angle α. R is the matched circular-arc radius at the junction with the main circular curve. Standard lemniscate proportioning used for highway transition design. Concept / Approach: In the polar formulation of a lemniscate transition, radial distance r is a function of the polar angle and the matching radius R. For the selected family used in practice, the maximum radial reach along the lemniscate develops as a sine function of twice the polar angle, scaled by a constant factor tied to R. Step-by-Step Solution (parameter reasoning): Relate the transition geometry to the adjoining circle of radius R at the junction.Use the standard lemniscate proportion that produces r proportional to sin(2α) at the limit angle.This leads to r_max = 3 * R * sin(2α) for the adopted family. Verification / Alternative check: Design handbooks tabulate lemniscate offsets and polar relations. The dependency on sin(2α) matches the symmetry of the curve lobes and its curvature progression, providing a quick check during layout. Why Other Options Are Wrong: 3 R sin α and 3 R sin(α/2): wrong angular argument; do not reflect the curve’s two-lobed symmetry. 3 R sin2α (without space) is dimensionally the same as option (c) but is a typographic variant; the intended correct relation uses sin(2α). None of these: incorrect since a standard closed-form exists for the selected family. Common Pitfalls: Confusing lemniscate properties with clothoid (Euler spiral) formulas. Mixing degrees and radians in trigonometric evaluation. Final Answer: 3 R sin 2α

Highway Engineering Questions