HKDSE Geography｜Transport Systems and Sustainable Transport Lesson-Prep Guide (for tutors)｜Rail versus road capacity, congestion time costs, emissions per passenger-km and policy trade-offs

2026-11-03

Tutor lesson-prep guides · Secondary Geography

Students stop at building railways reduces congestion, yet cannot say how many people a railway carries or how much carbon it saves. This lesson uses three computable numbers (72,000, 8,400 and 390) to turn a policy slogan into a comparison students can defend.

Objectives — Students can: (1) compute single-direction rail capacity as cars times capacity times departures, reaching 72,000 passengers an hour, and compare it with 8,400 for a three-lane road, a factor of about 8.6; (2) compute the time cost of congestion, with a 12 km trip rising from 18 to 48 minutes, an extra 30 minutes, and say who bears that cost; (3) use emissions per passenger-km (170 g by car, 40 g by rail) to derive 1.56 kg saved per trip, then scale to 500 commuters making two trips on 250 days for about 390 tonnes, and use those figures to evaluate public transport investment against road pricing.

01 Prerequisites (3-minute check)

If any of these fails, fix it before the lesson starts.

Skill	Quick check	Pass mark
Urban land use	Where is the CBD usually found?	At the centre or at the transport node, where rent peaks
Population density	How is density calculated?	Population divided by area
Greenhouse gases	Which greenhouse gas dominates transport emissions?	Carbon dioxide
Transport modes	What mainly separates public from private transport?	Passenger efficiency and road space used

02 Lesson flow (60 minutes)

Time	Stage	Tutor does	Student does
0–8 min	Three numbers first	72,000, 8,400, 8.6 times	Calculate before policy
8–18 min	Rail capacity	8 cars times 300 times 30 departures	Departures are the multiplier
18–30 min	Road capacity	2000 vehicles times 3 lanes times 1.4	Occupancy decides efficiency
30–42 min	Congestion cost	18 minutes becomes 48	Speed loss is not linear
42–52 min	Emissions	1.56 kg per trip, 390 tonnes a year	Compare per passenger-km
52–60 min	Policy evaluation and exit	Public transport versus road pricing	Defend a position with numbers

03 Teaching script (read it out)

Scene 1: Compute capacity before discussing policy

Ask: an 8-car train carrying 300 each, every 2 minutes, how many passengers per hour one way? Three steps: 8 times 300 is 2400, 60 divided by 2 is 30 departures, so 2400 times 30 is 72,000. Then the road: 3 lanes at 2000 vehicles with 1.4 people each gives 8,400. Once the 8.6-fold gap appears, students explain the policy bias themselves and you never have to say the word green.

Ask: why does one bus carry more than one car on the same road? (Occupancy, not speed)

Scene 2: Use time, not queues, to teach congestion

The most direct cost of congestion is time. At a free-flow 40 km/h a 12 km trip takes 18 minutes; at 15 km/h it takes 48, an extra 30 minutes, or an hour a day return. That is working time and family time, not an abstraction. Have students run the same line on their own school journey and the argument for road pricing stops sounding like moralising.

Ask: when speed falls from 40 to 15, by how much does time rise? (More than double, not thirty per cent)

Scene 3: Measure emissions per person

A car emits about 170 g per passenger-km and rail about 40 g. Over 12 km that is 2.04 kg against 0.48 kg, a saving of 1.56 kg. With 500 commuters, two trips, 250 days, that is 250,000 trips and roughly 390 tonnes a year. Per-passenger units are what stop the argument that a bus emits more than a car from being a fallacy, and they underpin every transport comparison in the paper.

Ask: a bus emits more than a car, so why is it greener? (Divide by passengers)

04 Question types and worked steps

Type	Example	Steps	Answer
Calculation	An 8-car train, 300 per car, every 2 minutes: hourly capacity one way?	Cars times capacity, then times departures	72,000 passengers an hour
Comparison	Compare rail with a three-lane road.	Convert both to passengers per hour, then divide	About 8.6 times
Data inference	How much carbon do 500 switchers save a year?	Saving per trip times trips, then convert to tonnes	About 390 tonnes
Policy evaluation	Can road pricing reduce congestion?	Cover price incentive, alternatives and equity	A position with conditions

Sanity check (teach this): Rail capacity is cars times capacity times departures: 8 times 300 is 2400, times 30 is 72,000; road capacity is lane flow times lanes times occupancy: 2000 times 3 is 6,000 vehicles, times 1.4 is 8,400 people; the 8.6-fold figure compares passengers per hour, not speeds; time equals distance over speed, so 12 at 40 is 18 minutes and at 15 is 48; halving speed more than doubles time because speed is the denominator; emissions comparisons must be per passenger-km or buses always lose; 390 tonnes is a model estimate and answers should say about and state assumptions; a policy answer needs a position, conditions and limits, since a list of benefits is not an evaluation.

05 Independent practice (3 questions)

Question	Answer	What to watch
Calculate: 6 cars, 250 each, every 3 minutes, hourly capacity one way?	30,000 passengers an hour	6 times 250 is 1,500; 60 over 3 is 20; 1,500 times 20
Compare: a car at 170 g/km and rail at 40 g/km over 20 km, what is emitted?	3.4 kg and 0.8 kg	Grams times kilometres, divided by 1,000
Evaluate: how does road pricing affect low-income commuters?	Affordability falls without parallel public transport concessions	Name the affected group

06 Common mistakes and what to say

Mistake	Student writes	Say this
Forgetting the departure frequency	A student computes 2,400 passengers an hour.	Tutor line: “You counted one train, not one hour. Departures are the multiplier.”
Comparing efficiency by speed	A student writes that rail carries more because it is faster.	Tutor line: “Fast is not the same as full. Compare how many people cross the section each hour.”
Emissions without dividing by passengers	A student writes that buses are the worst because they emit most.	Tutor line: “One bus carries a hundred people. Divide before you judge; the unit is per passenger-km.”
A policy answer with benefits only	A student writes that road pricing always works.	Tutor line: “It works only if an alternative exists. Without one you just move the queue.”

07 Homework (paper, section and question numbers)

Secondary Geography chapter index — Review the urban and industry chapters and copy the three anchors
S5 Geography: industry and manufacturing — Use its location factors to explain why logistics clusters at ports
S6 Geography: the sustainable city — Apply its land-use ideas to transport nodes

08 Exit check (last 5 minutes)

Question	Answer	Decision
How is rail capacity per hour computed?	Cars times capacity times departures	Missing departures means one train only
Speed falls from 40 to 15, what happens to time?	18 minutes becomes 48, an extra 30	Saying almost the same means no calculation
Which unit do emissions comparisons use?	Per passenger-kilometre	Per vehicle makes the comparison invalid

09 Tutor FAQ

Which year group?

S6 Geography transport; S5 can extend from urban issues.

How many figures must be memorised?

Three anchors: 72,000, 8,400 and 1.56 kg.

Is there calculation practice?

Three items with answers, including variants with different cars and frequencies.

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A TutorZone lesson-prep guide. Written by the TutorZone team; questions and lesson flow are original and are not taken from any school or publisher material.