LESSON 8.2 — Transport Planning Process, Traffic Surveys & Studies
A. Standard Map
| Topic | Governing Source | Exam Focus |
|---|---|---|
| Transport planning process | Classic UTPS 4-step model | Steps in order |
| Four-step model | Trip generation → Trip distribution → Modal split → Trip assignment | Output of each step |
| Travel demand forecasting | Land use + socioeconomic → trips | Inputs to generation |
| Trip types | HBW, HBO, NHB | Definitions |
| Survey types | OD, cordon, screenline, classified volume, spot speed, speed-delay, parking, accident | Purpose + setup |
| PCU — passenger car unit | Conversion of mixed traffic to a common unit | PCU values by mode |
| Traffic volume studies | AADT, ADT, peak hour factor | Definitions + arithmetic |
| Speed studies | Spot speed, journey speed, running speed, 85th percentile | Definitions |
| Capacity and Level of Service (LOS) | HCM; IRC:106 | LOS A-F classification |
| Land use – transport linkage | Interactive; transit-oriented development (TOD) | Principles |
B. Why It’s Used
Paper II §8 of the TGPSC syllabus specifies “transport planning process, traffic surveys and studies, land use and transportation planning.” Transport planning is the quantitative backbone of urban planning — it converts population, employment, and land-use data into trips, modal choices, and network loads. The Town Planning Assistant will encounter this material in Comprehensive Mobility Plans (CMPs), Detailed Project Reports (DPRs) for metro/bus systems, traffic-impact assessments (TIAs) for major developments, and master-plan transport chapters. The exam tests the 4-step model sequence, survey types and their purposes, PCU arithmetic, capacity and LOS concepts, and the land-use-transport linkage that justifies transit-oriented development.
C. Mechanism in Words
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Transport planning is the systematic process of forecasting future travel demand and designing transport infrastructure to meet it efficiently. The classical Urban Transportation Planning System (UTPS), developed in the United States in the 1950s–60s for the Chicago Area Transportation Study, is the global standard. It comprises the four-step model: (1) Trip Generation — how many trips originate in or are destined for each zone? (2) Trip Distribution — where do those trips go (origin-destination pairs)? (3) Modal Split — what share of trips uses which mode (walk, cycle, bus, car, metro)? (4) Traffic Assignment — which routes do the trips take on the network? Each step builds on the previous one; the output is the design volume on each link of the transport network.
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Step 1 — Trip Generation converts land-use and socioeconomic data into numbers of trips per zone. Inputs: population, employment (by sector), vehicle ownership, income, household size, school enrolment, retail floor area. The standard unit of analysis is the Traffic Analysis Zone (TAZ) — a small geographic unit, typically 1,000–5,000 households, that is the source or sink of trips. Trip-generation models are typically regression-based (trips per household as a function of income, car ownership, household size) or category-based (cross-classification of households by car ownership × household size). Trips are classified by purpose: Home-Based Work (HBW) — commuting trips between home and workplace; Home-Based Other (HBO) — trips from home to non-work destinations (shopping, school, recreation); Non-Home-Based (NHB) — trips not starting or ending at home (work-to-shopping, work-to-lunch). HBW trips are typically the most regular and predictable; HBO and NHB more variable.
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Step 2 — Trip Distribution connects trip origins to destinations, producing an Origin-Destination (OD) matrix. The most common method is the Gravity Model: trips from zone i to zone j = (Production of zone i × Attraction of zone j × Friction factor) / sum of all attractions. The friction factor reflects the impedance (resistance) of travel between zones — typically a function of travel time, distance, or cost; longer trips are less likely. Other methods include the Fratar method (growth-factor-based, used when no impedance data is available) and the Intervening Opportunities Model (probability of trip ending at the nearest acceptable destination). The output is an OD matrix showing trips between every pair of zones.
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Step 3 — Modal Split divides trips among available modes. This is the most policy-sensitive step — it determines whether the city will be car-dominated, transit-oriented, or cycling-pedestrian friendly. Inputs: trip length (short trips favour walking/cycling), income (higher income favours private vehicles), car ownership, transit availability, journey time by mode. Models range from simple binomial (car vs transit) to complex multinomial logit models considering multiple mode options. Indian cities typically have a transit + non-motorised majority — nationally, only about 10–20% of trips are by private car in most large cities; the rest are by bus, metro, IPT (intermediate public transport — auto-rickshaws, taxis), walk, and cycle. The “captive” vs “choice” rider distinction is important: captive riders (low income, no car) use transit/walk/cycle by default; choice riders can be attracted to transit only if it is competitive on time, cost, and comfort.
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Step 4 — Traffic Assignment routes the trips on the network to determine link volumes. The principle: travellers choose the route that minimises their generalised cost (a weighted combination of time, distance, operating cost, toll, comfort). Common assignment methods: All-or-Nothing (AON) — all trips between an OD pair take the shortest path (a simplification); User Equilibrium (UE) — travellers distribute across multiple routes until no traveller can reduce their cost by switching (Wardrop’s first principle); Stochastic User Equilibrium — accounts for the fact that travellers have imperfect knowledge of routes; Dynamic Traffic Assignment — accounts for time-varying demand (e.g., peak vs off-peak). The output of traffic assignment is the design volume on each link, which feeds back into capacity assessments, junction design, and infrastructure prioritisation.
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Traffic surveys provide the empirical data that calibrate and validate the four-step model. Major survey types: Origin-Destination (OD) survey — captures where trips start and end; conducted by household interview (1–5% sample), roadside interview (at cordon points), or returning-postcard method. Cordon survey — interview all vehicles crossing an imaginary cordon line around the study area to identify trips entering/leaving. Screenline survey — counts vehicles crossing a screenline (a natural barrier like a river or rail line) to validate that assigned OD trips match observed counts. Classified Volume Count (CVC) — counts vehicles by type (car, two-wheeler, auto, bus, truck, cycle) over time (typically 16-hour or 24-hour); used to compute AADT and PCU. Spot Speed Study — measures speed of individual vehicles at a point using radar or loop detectors. Speed-and-Delay Study — measures journey speed and identifies delay causes (using the moving-observer method, license-plate matching, or GPS tracking). Parking Survey — inventory of parking supply, occupancy, turnover, duration. Accident Study — analysis of crash data by location, time, severity, cause. Each survey has a specific purpose and a specific data-collection protocol; together they form the empirical basis for transport planning.
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The Passenger Car Unit (PCU) is the standard way to convert mixed traffic into a common unit for capacity analysis. Different vehicle types occupy different road space and travel at different speeds — a truck is not equivalent to a motorcycle. The PCU is a weighting factor that expresses how many passenger cars would have the same traffic-impact as one vehicle of the given type. IRC:106 provides PCU values for Indian conditions. Typical PCU values (urban, mid-block): car = 1.0; two-wheeler (motorcycle/scooter) = 0.25–0.5; auto-rickshaw = 0.5–1.0; cycle = 0.2–0.5; bus = 2.5–3.0; truck (light) = 1.5–2.0; truck (heavy) = 3.0–4.5; cycle-rickshaw = 1.0–1.5; bullock cart = 8.0–10.0 (rural). PCU values vary by terrain (urban vs rural), traffic composition, and speed; they should be applied with the appropriate context.
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Capacity and Level of Service (LOS) translate traffic volumes into operational performance. Capacity is the maximum number of vehicles (or PCUs) that can pass a point per hour under prevailing conditions; it depends on lane width, lateral clearance, gradient, and traffic composition. Level of Service (LOS) is a qualitative measure describing operational conditions — A (free flow, no constraint) through F (breakdown, forced flow). The Highway Capacity Manual (HCM, US) defines six LOS classes A-F; IRC:106 adapts for Indian conditions using Volume-to-Capacity (V/C) ratio bands. Typical LOS for Indian planning: LOS A (V/C < 0.20 — free flow); LOS B (0.20–0.40 — reasonably free flow); LOS C (0.40–0.60 — stable flow, comfortable); LOS D (0.60–0.80 — approaching unstable flow, acceptable); LOS E (0.80–1.00 — unstable flow, at capacity); LOS F (>1.00 — breakdown, forced flow). Most urban Indian roads operate at LOS D-F during peak hours.
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Land use and transport are tightly coupled — each shapes the other. Transport infrastructure changes land accessibility, which changes land value, which changes land use (e.g., a new metro station raises nearby property values and attracts high-density development). Conversely, land use generates travel demand (a new office complex creates commuting trips). This is the land-use-transport feedback cycle. Transit-Oriented Development (TOD) is the planning approach that consciously uses this cycle — concentrating high-density, mixed-use development around transit stations to maximise transit ridership and reduce car dependence. India’s TOD policies (MoHUA’s TOD policy 2014; state-level TOD policies in Delhi, Maharashtra, Karnataka, Telangana) integrate FSI incentives, parking maximums, and walkable-street design within walking distance (typically 800 m) of metro/BRT stations.
D. Core Concept Explanations
C1. Four-step model — outputs
| Step | Output |
|---|---|
| Trip generation | Productions and attractions by zone (e.g., zone A produces 1,000 trips, attracts 800) |
| Trip distribution | OD matrix (e.g., 200 trips from zone A to zone B) |
| Modal split | Trips by mode (e.g., 100 by car, 70 by bus, 30 by walk) |
| Trip assignment | Volume on each link (e.g., 600 PCU/hour on Link X) |
C2. PCU values (urban, IRC:106 indicative)
| Vehicle type | PCU (urban mid-block) |
|---|---|
| Car / Jeep / Van | 1.0 |
| Two-wheeler (motorcycle/scooter) | 0.25–0.5 |
| Auto-rickshaw | 0.5–1.0 |
| Cycle (bicycle) | 0.2–0.5 |
| Cycle-rickshaw | 1.0–1.5 |
| Bus | 2.5–3.0 |
| Truck (light) | 1.5–2.0 |
| Truck (heavy) | 3.0–4.5 |
| Bullock cart (rural) | 8.0–10.0 |
C3. LOS classification (IRC:106 indicative V/C bands)
| LOS | V/C ratio | Description |
|---|---|---|
| A | < 0.20 | Free flow; no constraint |
| B | 0.20–0.40 | Reasonably free flow |
| C | 0.40–0.60 | Stable flow; comfortable |
| D | 0.60–0.80 | Approaching unstable; acceptable |
| E | 0.80–1.00 | Unstable; at capacity |
| F | > 1.00 | Breakdown; forced flow |
C4. Survey types — purpose and method
| Survey | Purpose | Method |
|---|---|---|
| Origin-Destination (OD) | Capture where trips start/end | Household interview; roadside interview; postcard |
| Cordon | Identify trips entering/leaving an area | Interview all vehicles at cordon line |
| Screenline | Validate OD assignments | Count vehicles crossing screenline (river, rail) |
| Classified Volume Count (CVC) | AADT, PCU computation | Manual or automatic count by vehicle type, 16-24 h |
| Spot speed study | Speed at a point | Radar; loop detectors |
| Speed-and-delay study | Journey speed; delay sources | Moving-observer; license-plate matching; GPS |
| Parking survey | Supply, occupancy, turnover | Inventory + occupancy observation |
| Accident study | Crash patterns | Police records; site analysis |
C5. Trip types — definitions
| Code | Trip purpose | Example |
|---|---|---|
| HBW | Home-Based Work | Home to office |
| HBO | Home-Based Other | Home to shopping, school, recreation |
| NHB | Non-Home-Based | Office to shopping; shopping to restaurant |
E. Worked Numericals and Parameter Tables
E1. PCU computation
A road carries in one hour: 400 cars, 600 two-wheelers, 100 autos, 50 buses, 200 cycles. Using PCU values: car = 1.0; two-wheeler = 0.3; auto = 0.8; bus = 3.0; cycle = 0.3.
- Cars: 400 × 1.0 = 400 PCU
- Two-wheelers: 600 × 0.3 = 180 PCU
- Autos: 100 × 0.8 = 80 PCU
- Buses: 50 × 3.0 = 150 PCU
- Cycles: 200 × 0.3 = 60 PCU
- Total: 870 PCU/hour
E2. AADT computation
A 7-day classified count at a location gives daily volumes (in vehicles): Mon 8,000; Tue 8,200; Wed 8,400; Thu 8,600; Fri 9,000; Sat 7,200; Sun 5,000. Average = (8000 + 8200 + 8400 + 8600 + 9000 + 7200 + 5000) / 7 = 54,400 / 7 ≈ 7,771 vehicles/day (AADT). If peak hour is 8% of AADT, peak hour volume = 0.08 × 7771 ≈ 622 vehicles/hour.
E3. Capacity and LOS — worked
A 2-lane road has a capacity of 2,000 PCU/hour (per direction, both lanes combined). If observed volume is 1,500 PCU/hour: V/C = 1500/2000 = 0.75 → LOS D (approaching unstable, acceptable). If volume rises to 1,700: V/C = 0.85 → LOS E (at capacity). If 2,200: V/C = 1.10 → LOS F (breakdown).
E4. Gravity model — simplified
Trips from zone A (produces 1000 trips) to zone B (attracts 800 trips), with friction factor F_AB = 0.5; sum of all attractions = 4000.
- T_AB = (1000 × 800 × 0.5) / 4000 = 100 trips
This is the simplest form; real models use multiple zones and calibrated friction factors.
F. Design Criteria
| Parameter | Standard / Typical value | Source |
|---|---|---|
| PCU: car | 1.0 | IRC:106 |
| PCU: two-wheeler | 0.25–0.5 | IRC:106 |
| PCU: bus | 2.5–3.0 | IRC:106 |
| LOS classes | 6 (A-F) | HCM; IRC:106 |
| LOS A V/C | < 0.20 | IRC:106 |
| LOS F V/C | > 1.00 | IRC:106 |
| Typical peak hour factor | 8–12% of AADT | Transport planning convention |
| TAZ size | 1,000–5,000 households | Transport planning convention |
| TOD walkable radius | ~800 m (10-min walk) | MoHUA TOD policy |
G. Application Zones
- Comprehensive Mobility Plans (CMP) — every metropolitan city has a CMP that follows the 4-step model.
- Detailed Project Reports for metro/bus — DPRs forecast ridership using the 4-step model.
- Traffic Impact Assessment (TIA) — for major developments (malls, IT parks, large townships).
- Road capacity assessment — LOS evaluation drives widening/signal/grade-separation decisions.
- TOD planning — Hyderabad HMDA TOD policy; metro station area plans.
H. Common Confusions
| Confusion | Reality |
|---|---|
| “The 4-step model is linear; it doesn’t iterate.” | False — the model iterates with feedback from assignment back to generation/distribution. |
| “PCU is the same as one vehicle.” | No — PCU is a weighting factor; a bus is 2.5–3.0 PCU, a cycle is 0.2–0.5 PCU. |
| “LOS A is the worst.” | False — LOS A is free flow (best); LOS F is breakdown (worst). |
| “HBW trips are less predictable than NHB.” | False — HBW (home-based work) trips are the most regular and predictable. |
| “Cordon and screenline surveys are identical.” | No — cordon surrounds an area; screenline is a single line across the area. |
| “Spot speed study and speed-and-delay study are the same.” | No — spot speed is at a point; speed-and-delay is along a route with delay identification. |
| “Capacity and AADT are the same.” | No — capacity is max possible hourly volume; AADT is average daily volume. |
I. Compare & Contrast
I1. Four-step model steps
| Step | Output |
|---|---|
| 1. Trip generation | Number of trips produced/attracted per zone |
| 2. Trip distribution | OD matrix |
| 3. Modal split | Trips by mode |
| 4. Trip assignment | Volume on each link |
I2. Spot speed study vs Speed-and-delay study
| Dimension | Spot speed | Speed-and-delay |
|---|---|---|
| Scope | Single point | Along a route |
| Output | Distribution of speeds at point | Journey speed; sources of delay |
| Method | Radar; loop detectors | Moving-observer; GPS |
| Use | Design speed; geometric design | Bottleneck identification |
J. Memory Hooks
- “G-D-M-A” — Generation, Distribution, Modal split, Assignment. The 4-step model.
- “HBW-HBO-NHB” — three trip purposes.
- “Car=1; bus=3; cycle=0.3” — three PCU anchor values.
- “A-best, F-worst” — LOS classification.
- “V/C bands: 0.20, 0.40, 0.60, 0.80, 1.00” — LOS thresholds.
- “OD-Cordon-Screenline-CVC-Spot-S&D-Parking-Accident” — 8 survey types.
- “TAZ = 1,000–5,000 households” — typical zone size.
- “TOD = 800 m walkable radius” — transit-oriented design.
K. Revision Ladder
| Order | Item | Time |
|---|---|---|
| 1 | Memorise the 4-step model with output of each step | 30 min |
| 2 | Memorise the 3 trip types (HBW, HBO, NHB) | 15 min |
| 3 | Memorise PCU values for major vehicle types | 30 min |
| 4 | Memorise the 8 survey types with purpose | 45 min |
| 5 | Memorise LOS A-F with V/C bands | 30 min |
| 6 | Practise PCU and AADT arithmetic | 30 min |
| 7 | Memorise the gravity model form | 15 min |
| 8 | Memorise TOD walkable radius and policy principles | 20 min |
| 9 | Map Telangana transport studies (Hyderabad CMP, metro DPR, SRDP) | 30 min |
L. Exam Traps
| Trap | Correct response |
|---|---|
| Question asks the order of the 4-step model. | Generation → Distribution → Modal split → Assignment. |
| Question lists LOS A as worst. | False — LOS A is best (free flow); F is worst. |
| Question lists PCU of bus as 1.0. | False — bus is 2.5–3.0 PCU. |
| Question asks the V/C threshold for LOS F. | > 1.00. |
| Question pairs HBW with “variable, hard to predict.” | False — HBW is the most regular and predictable. |
| Question lists cordon survey as covering a single line. | False — cordon surrounds an area; screenline is a single line. |
| Question pairs spot speed with route-level study. | False — spot speed is at a single point. |
| Question asks TOD walkable radius. | ~800 m (10-minute walk) from a metro/BRT station. |
M. Answer-Writing Cues
- For model questions, sequence the steps explicitly: “The classical UTPS four-step model comprises (1) Trip Generation, (2) Trip Distribution, (3) Modal Split, and (4) Trip Assignment; the output of step 4 is the link volume on each road segment.”
- For survey questions, give type + purpose + method + use: “A Classified Volume Count (CVC) measures vehicles by type over 16–24 hours; it provides the empirical basis for AADT and PCU computations.”
- For LOS questions, give class + V/C + description: “LOS D corresponds to V/C 0.60–0.80 — approaching unstable flow, but operationally acceptable.”
- For TOD questions, give definition + radius + FSI principle.
N. PYQ Integration
Pattern questions only:
Pattern question 1 — 4-step model
Q. The classical four-step urban transport planning model, in correct sequence, is:
– (A) Modal split → Trip generation → Trip distribution → Assignment
– (B) Trip generation → Trip distribution → Modal split → Trip assignment ✓
– (C) Trip distribution → Trip generation → Assignment → Modal split
– (D) Assignment → Modal split → Distribution → Generation
Ans: (B). Generation → Distribution → Modal split → Assignment.
Pattern question 2 — PCU
Q. The Passenger Car Unit (PCU) of a standard bus, per IRC:106, is approximately:
– (A) 1.0
– (B) 1.5
– (C) 2.5–3.0 ✓
– (D) 5.0
Ans: (C).
Pattern question 3 — LOS
Q. Level of Service (LOS) F corresponds to a V/C ratio of:
– (A) < 0.20
– (B) 0.40–0.60
– (C) 0.80–1.00
– (D) > 1.00 ✓
Ans: (D). LOS F = breakdown.
Pattern question 4 — MSQ
Q. Which of the following are standard traffic surveys used in transport planning?
– (A) Origin-Destination survey ✓
– (B) Classified Volume Count ✓
– (C) Speed-and-delay study ✓
– (D) Soil bearing capacity test
Ans: (A), (B), (C). Soil test is a structural engineering concern, not a transport survey.
Pattern question 5 — Numerical
A road carries 300 cars, 400 two-wheeler, 50 buses, and 100 cycles in an hour. With PCU values car=1.0, two-wheeler=0.3, bus=3.0, cycle=0.3, the total PCU/hour is:
– (A) 450
– (B) 600 ✓
– (C) 760
– (D) 1000
Ans: (B). Cars 300×1.0 = 300; two-wheelers 400×0.3 = 120; buses 50×3.0 = 150; cycles 100×0.3 = 30. Total = 300 + 120 + 150 + 30 = 600 PCU/hour.
O. Mini-Check — Lesson 8.2
- State the four steps of the UTPS model in order.
- Define HBW, HBO, and NHB trips.
- State the typical PCU of a car, a two-wheeler, and a bus.
- State the six LOS classes and the V/C band for LOS A and LOS F.
- Name six traffic survey types and their purposes.
- What is the difference between a cordon survey and a screenline survey?
- State the standard form of the gravity model.
- State the typical peak hour factor (% of AADT).
- State the typical TAZ size in households.
- State the TOD walkable radius.
Answers:
1. Trip Generation → Trip Distribution → Modal Split → Trip Assignment.
2. HBW = Home-Based Work (commuting); HBO = Home-Based Other (shopping, school, recreation); NHB = Non-Home-Based (neither end at home).
3. Car = 1.0; two-wheeler = 0.25–0.5; bus = 2.5–3.0 (per IRC:106).
4. Six classes: A (best) through F (worst). LOS A = V/C < 0.20 (free flow); LOS F = V/C > 1.00 (breakdown).
5. OD (origin-destination); Cordon (area boundary); Screenline (validation across a barrier); CVC (volume by vehicle type); Spot speed (speed at a point); Speed-and-delay (journey speed + delay sources). Any six.
6. Cordon surrounds an area and identifies trips entering/leaving; screenline is a single line across an area (river, rail) used to validate OD assignments.
7. T_ij = (P_i × A_j × F_ij) / Σ A, where P = production, A = attraction, F = friction (impedance) factor.
8. Typically 8–12% of AADT.
9. 1,000–5,000 households per TAZ.
10. ~800 m (10-minute walk) from a metro/BRT station.
Next: Lesson 8.3 — Parking, Signals, Street Lighting & Traffic Management.