Chartered Civil Engineer (ICE) Transportation and Highway Engineering Flashcards

24 sample cards from the Transportation and Highway Engineering deck

Sampled from the end of the deck, so these are different cards from the ones shown on the syllabus page.

1. What are the four foundation classes used in DMRB CD 225, and what defines them?

   Foundation Classes 1–4, defined by their long-term surface (top-of-foundation) stiffness modulus: Class 1 $\geq 50$ MPa, Class 2 $\geq 100$ MPa, Class 3 $\geq 200$ MPa, Class 4 $\geq 400$ MPa. Higher classes permit thinner upper pavement layers.

2. Distinguish between the empirical (CBR) and the analytical (mechanistic) methods of flexible pavement design.

   The empirical method relies on observed performance correlations (e.g. CBR–thickness charts, Road Note 29). The analytical (mechanistic) method models the pavement as an elastic multilayer system, computing critical strains (horizontal tensile strain at the base of bituminous layers; vertical compressive strain at the subgrade top) and checking them against fatigue and deformation criteria.

3. In analytical pavement design, what two critical strains are typically checked and what failure mode does each control?

   Horizontal tensile strain at the underside of the bound (asphalt) layers — controls fatigue cracking. Vertical compressive strain at the top of the subgrade — controls rutting/permanent deformation.

4. What is bitumen, and what is the difference between penetration-grade and polymer-modified bitumen?

   Bitumen is the viscous hydrocarbon binder (residue of crude oil refining) that binds aggregate in asphalt. Penetration-grade bitumen is classified by needle penetration (e.g. 40/60 pen). Polymer-modified bitumen (PMB) has polymers (e.g. SBS) added to improve elasticity, rutting resistance and temperature performance.

5. Name three common UK asphalt surface course materials and a key property of each.

   Stone Mastic Asphalt (SMA) — durable, rut-resistant, good texture; Hot Rolled Asphalt (HRA) — gap-graded, durable, needs pre-coated chippings for skid resistance; Porous Asphalt / Thin Surface Course Systems (TSCS) — reduce noise and spray, provide drainage and texture.

6. Define skid resistance and the property measured by SCRIM.

   Skid resistance is the friction between tyre and road surface, vital for safe braking and cornering. SCRIM (Sideway-force Coefficient Routine Investigation Machine) measures the sideways force coefficient (SFC/CSC) of the wet road surface to monitor and manage skidding risk.

7. What is the difference between 'macrotexture' and 'microtexture' of a road surface?

   Microtexture is the fine-scale roughness of individual aggregate particles, providing wet skid resistance at low speeds. Macrotexture is the larger-scale surface texture (gaps between aggregate), aiding water drainage and skid resistance at higher speeds; measured as Texture Depth (e.g. Sensor-Measured Texture Depth, SMTD).

8. What is reflective (reflection) cracking in pavements and where does it occur?

   Reflective cracking is the propagation of cracks or joints from an underlying layer up through a new overlay, mirroring the position of the joint/crack below. It commonly occurs where a bituminous overlay is laid over jointed concrete or cracked existing pavement.

9. Distinguish between routine, preventive, and structural (rehabilitation) pavement maintenance.

   Routine maintenance: reactive minor repairs (pothole patching, crack sealing). Preventive maintenance: timely surface treatments (e.g. surface dressing) to extend life before deterioration. Structural maintenance/rehabilitation: overlays, inlays or reconstruction to restore load-carrying capacity.

10. What is surface dressing and what is its primary purpose?

    Surface dressing is a preventive treatment of spraying bitumen binder onto the carriageway followed by chippings rolled in. Its purpose is to seal the surface against water ingress and restore skid resistance/texture — it adds little structural strength.

11. Define pavement asset management and name a key UK indicator used to assess road condition.

    Pavement asset management is the systematic, lifecycle-based process of maintaining road assets at agreed service levels for least whole-life cost. UK condition indicators include SCANNER surveys, the Road Condition Index (RCI), and deflection (e.g. FWD/Deflectograph) measurements.

12. What does a Falling Weight Deflectometer (FWD) measure and why is it used?

    An FWD applies an impulse load simulating a moving wheel and measures the resulting deflection bowl with geophones. The deflection data are back-analysed to estimate layer stiffness moduli and residual structural life for rehabilitation design.

13. State the fundamental relationship of traffic flow theory linking flow, speed and density.

    $$q = k\,v$$ where $q$ is flow (veh/h), $k$ is density (veh/km) and $v$ is space-mean speed (km/h). This is the fundamental identity of traffic flow.

14. Describe Greenshields' linear speed–density model and the resulting flow–density relationship.

    Greenshields assumes a linear speed–density relation: $$v = v_f\left(1 - \frac{k}{k_j}\right)$$ where $v_f$ is free-flow speed and $k_j$ jam density. Substituting into $q=kv$ gives a parabolic flow–density curve; maximum flow (capacity) occurs at $k_j/2$ with $v=v_f/2$, giving $q_{max}=\frac{v_f k_j}{4}$.

15. Define capacity, level of service (LOS), and saturation flow in traffic engineering.

    Capacity: maximum sustainable flow a facility can carry under prevailing conditions (veh/h). Level of Service (LOS A–F): qualitative measure of operating quality based on delay/density/speed. Saturation flow: maximum discharge rate from a signal stop-line during fully saturated green (pcu/h of green).

16. At a signalised junction, give Webster's formula for the optimum cycle time.

    $$C_o = \frac{1.5L + 5}{1 - Y}$$ where $C_o$ is optimum cycle time (s), $L$ the total lost time per cycle (s), and $Y$ the sum of the critical flow ratios $\sum (q/s)$ for the phases.

17. How is effective green time related to displayed green and lost time at a signal?

    $$g = G + A - \ell$$ Effective green $g$ equals displayed green $G$ plus amber $A$ minus the total lost time $\ell$ (start-up lost time plus end lag). Capacity of an approach $= s\cdot g/C$, where $s$ is saturation flow and $C$ the cycle time.

18. What is the four-stage transport model and name its stages in order?

    The classic four-stage (sequential) transport model: 1. Trip Generation (how many trips), 2. Trip Distribution (origin–destination pattern), 3. Modal Split (choice of mode), 4. Trip/Traffic Assignment (route choice onto the network).

19. Describe the gravity model used in trip distribution.

    The gravity model estimates trips $T_{ij}$ between zones proportional to trip-end productions/attractions and inversely related to a deterrence (cost/impedance) function: $$T_{ij} = a_i b_j O_i D_j f(c_{ij})$$ where $O_i$, $D_j$ are origins/destinations, $f(c_{ij})$ the deterrence function of cost $c_{ij}$, and $a_i,b_j$ balancing factors.

20. What is the logit model used for in transport modelling, and give the binary logit choice probability.

    The logit model represents discrete choice (e.g. mode or route choice) based on utility. The probability of choosing alternative 1 over 2 is: $$P_1 = \frac{e^{U_1}}{e^{U_1}+e^{U_2}} = \frac{1}{1+e^{-(U_1-U_2)}}$$ where $U$ are the (random) utilities of each alternative.

21. State Wardrop's first principle of traffic assignment (user equilibrium).

    Wardrop's first principle (user equilibrium): under equilibrium, the travel times on all used routes between an O–D pair are equal and no greater than those on any unused route; no individual driver can reduce their travel time by switching routes.

22. What is a Road Safety Audit (RSA) and at what stages is it carried out?

    A Road Safety Audit is a formal, independent examination of a road scheme to identify potential safety hazards for all users before/after it opens. It is carried out at defined stages: Stage 1 (preliminary/completion of preliminary design), Stage 2 (completion of detailed design), Stage 3 (completion of construction/before opening), and Stage 4 (post-opening monitoring).

23. Differentiate 'traffic calming' measures by their mechanism, giving two examples of each.

    Vertical deflection: road humps, speed cushions, raised tables — force speed reduction via vertical movement. Horizontal deflection: chicanes, build-outs, mini-roundabouts — force speed reduction via lateral movement. Both aim to lower speeds and improve safety in sensitive areas.

24. What is integrated transport policy, and name a UK mechanism used to manage travel demand.

    Integrated transport policy seeks to co-ordinate modes, land-use planning and pricing so the transport system functions as a coherent whole, promoting accessibility and sustainability. UK demand-management mechanisms include road user/congestion charging (e.g. London Congestion Charge), workplace parking levies, Travel Plans, and Low Emission Zones.

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