Every service costing chapter throws the same challenge at students: you learn the formulas for standing charges, running costs, and passenger-kilometres one by one, and then the exam hands you a single problem that expects you to combine all of them into one clean answer. This is exactly where comprehensive illustrations earn their name. They are not new theory. They are the theory you already know, stitched together into a realistic transport costing problem, so you can see how a bus company or a goods carrier actually works out its cost per kilometre. This post walks through that process step by step, using worked examples so you can see the logic, not just the final number.
Table of Contents
- Why comprehensive illustrations matter in service costing
- The three cost buckets you must sort first
- Illustration 1: Passenger transport and cost per passenger-kilometre
- The scenario
- Step 1: Calculate total kilometres
- Step 2: Calculate total passenger-kilometres
- Step 3: Build the operating cost sheet
- Step 4: Compute the final answers
- Illustration 2: Goods transport and the absolute versus commercial tonne-km debate
- The scenario
- Method 1: Absolute tonne-kilometres
- Method 2: Commercial tonne-kilometres
- Why the gap matters
- Illustration 3: Why fixed cost behaviour changes the answer as volume grows
- Common mistakes to watch for
- From the classroom to the boardroom
- What do you think?
Why comprehensive illustrations matter in service costing
Service costing, also called operating costing, is used by organisations that sell a service rather than a physical product – transport operators, hospitals, hotels, and power utilities are the classic examples covered in cost and management accounting courses. The study material prescribed for the Cost and Management Accounting paper treats service costing as a core topic precisely because its logic differs from manufacturing cost sheets: instead of costing a tangible unit like a product, you are costing an abstract composite unit such as a passenger-kilometre or a tonne-kilometre.
A single formula rarely reflects how messy real operations are. A transport company runs multiple buses on multiple routes, some days at full capacity and some days half-empty, with fuel costs that rise and fall independently of fixed costs like driver salaries. Comprehensive illustrations exist to train you to handle that messiness in one structured worksheet, called the operating cost sheet.
The three cost buckets you must sort first
Before touching any numbers, every transport costing illustration expects you to classify costs into three buckets. Get this classification wrong, and the entire cost sheet collapses.
| Cost type | Also called | Typical examples | Behaviour |
|---|---|---|---|
| Fixed costs | Standing charges | Driver and conductor salaries, insurance, road tax, depreciation, garage rent | Do not change with distance travelled |
| Variable costs | Running costs | Diesel, engine oil, lubricants | Rise and fall directly with kilometres run |
| Semi-variable costs | Maintenance charges | Repairs, tyres, spare parts | Partly fixed, partly linked to usage |
This classification is not academic hair-splitting. A standard operating cost sheet format for a transport company is built entirely around these three sections, and every comprehensive illustration you attempt will ask you to slot each expense into the correct row before you can compute a single cost-per-unit figure.
Illustration 1: Passenger transport and cost per passenger-kilometre
Let’s work through a full example the way a typical exam question would frame it.
The scenario
A city bus operator runs 4 buses on a 30-km route. Each bus makes 2 round trips a day and operates for 25 days a month. Seating capacity is 50 passengers per bus, and on average 80% of seats are occupied. Monthly costs are as follows: driver and conductor salaries, insurance and road tax, and depreciation together total ₹1,20,000 (standing charges); diesel and oil cost ₹90,000 (running costs); repairs and maintenance amount to ₹30,000 (semi-variable costs).
Step 1: Calculate total kilometres
A round trip on a 30-km route covers 60 km. Each bus does 2 round trips a day, so daily distance per bus is 120 km. Over 25 days, that is 3,000 km per bus, and across 4 buses:
Total kilometres = 4 buses × 25 days × 2 trips × 60 km = 12,000 km
Step 2: Calculate total passenger-kilometres
This is where composite cost units come in. Since occupancy is 80% of a 50-seat capacity, effective passengers per trip are 40. Passenger-kilometres are computed by multiplying total kilometres by the average number of passengers carried, which is exactly how composite units like passenger-km are defined in cost accounting – they combine two measures, distance and volume, into one meaningful unit.
Total passenger-kilometres = 12,000 km × 40 passengers = 4,80,000 passenger-km
Step 3: Build the operating cost sheet
| Particulars | Amount (₹) |
|---|---|
| Standing charges (salaries, insurance, tax, depreciation) | 1,20,000 |
| Running costs (diesel and oil) | 90,000 |
| Maintenance costs (repairs) | 30,000 |
| Total operating cost | 2,40,000 |
Step 4: Compute the final answers
Cost per kilometre = ₹2,40,000 ÷ 12,000 km = ₹20 per km
Cost per passenger-kilometre = ₹2,40,000 ÷ 4,80,000 passenger-km = ₹0.50 per passenger-km
Notice how the entire answer depends on getting Step 1 and Step 2 right. Everything after that is straightforward division. Most marks lost in this type of question come from miscounting round trips or forgetting to apply the occupancy percentage, not from the final arithmetic.
Illustration 2: Goods transport and the absolute versus commercial tonne-km debate
Passenger buses use passenger-km. Goods carriers use tonne-km, but here examiners add a twist: you must know two different ways to compute it.
The scenario
A truck starts from Station A carrying 8 tonnes of goods. It travels 50 km to Station B, unloads 3 tonnes, and continues 70 km to Station C carrying the remaining 5 tonnes. At Station C, it picks up 6 tonnes for the return leg and travels 90 km back to Station A.
Method 1: Absolute tonne-kilometres
Here, each leg of the journey is calculated separately and then added up. This method is described as the sum of tonne-kilometres arrived at by multiplying various distances by the respective load carried on each leg, rather than averaging the load across the whole trip.
(8 tonnes × 50 km) + (5 tonnes × 70 km) + (6 tonnes × 90 km)
= 400 + 350 + 540
Absolute tonne-km = 1,290
Method 2: Commercial tonne-kilometres
This method treats the entire trip as one unit. It multiplies the total distance travelled by the average load carried, giving a simpler but less precise picture.
Average load = (8 + 5 + 6) ÷ 3 = 6.33 tonnes
Total distance = 50 + 70 + 90 = 210 km
Commercial tonne-km = 6.33 × 210 ≈ 1,329
Why the gap matters
If the total trip cost is ₹19,350, the cost per absolute tonne-km works out to ₹15, while the cost per commercial tonne-km comes to roughly ₹14.56. The two figures rarely match exactly, and that is the point of the illustration: absolute tonne-km respects the actual load carried on each stretch of road, while commercial tonne-km smooths it into a single average. A goods transport company deciding freight rates for uneven, multi-stop routes needs to know which method it is using, because the underlying objective of transport costing is to fix the price or freight to be charged to customers accurately – an inflated or understated tonne-km figure directly changes the quoted rate.
Illustration 3: Why fixed cost behaviour changes the answer as volume grows
A third type of comprehensive illustration tests whether you understand cost behaviour rather than just formulas. Suppose the bus operator from Illustration 1 adds a fifth bus on the same route, keeping standing charges roughly unchanged in total (since one supervisor and one insurance policy can often cover the extra vehicle with only a modest increase) while running and maintenance costs rise proportionately with distance.
Total kilometres rise to 15,000 km (5 buses instead of 4), and suppose total cost rises to ₹2,85,000. Cost per kilometre now becomes ₹19 instead of ₹20. The average fixed cost per kilometre has fallen because standing charges are spread over a larger base, even though total cost went up. This is the practical insight examiners want you to draw: as an operating cost sheet scales up, the fixed cost component per unit shrinks, while the variable cost per unit stays roughly constant. Confusing “total cost rose” with “cost per unit rose” is one of the most common errors in comprehensive illustrations.
Common mistakes to watch for
A few errors show up repeatedly across comprehensive illustrations, regardless of whether the question is about buses, trucks, or hospitals:
- Forgetting round trips. A “40 km route” often means 80 km for a return journey, and missing this doubles or halves your final answer.
- Mixing up absolute and commercial tonne-km. Always re-read the question to see which method it explicitly asks for.
- Applying occupancy percentage incorrectly. It should be applied to seating capacity, not to total kilometres directly.
- Misclassifying semi-variable costs. Depreciation is fixed in most illustrations, but if the question states it is calculated on a per-kilometre basis, it moves into the variable category instead.
- Skipping the operating cost sheet format. Jumping straight to a final number without laying out standing, running, and maintenance charges separately makes errors much harder to spot and correct.
From the classroom to the boardroom
These illustrations are not just exam drills. A real transport company uses the exact same operating cost sheet logic to decide whether a new route is profitable, whether to quote a lower fare to win a school bus contract, or whether rising diesel prices justify a fare hike. The averaging described in operating cost sheets, where fixed, variable, and maintenance costs are collected and divided by total units carried, is precisely how logistics firms in India benchmark their per-kilometre cost against competitors before bidding for freight contracts. Understanding the mechanics behind the illustration means understanding how a transport business actually prices its services and protects its margins.
What do you think?
What do you think? If fuel prices rose by 15% next month, would you expect the cost per passenger-kilometre in Illustration 1 to rise by the same percentage, or by less? And between absolute and commercial tonne-km, which method do you think gives a fairer basis for quoting freight rates to a customer on a multi-stop route?
References
- https://www.icai.org/post/sm-intermediate-paper4
- https://www.arsdcollege.ac.in/wp-content/uploads/2020/04/Service-Costing.pdf
- https://live.icai.org/bos/vcc/pdf/01042022_Dr__N_N__Sengupta_Ch-1_Introduction_to_CMA_1648787070.pdf
- https://www.arsdcollege.ac.in/wp-content/uploads/2020/03/OPERATING-COSTING.pdf
- https://www.udhnacollege.ac.in/uploads/group/content/51c43717-b8dd-4433-93b6-28e17fd9acaa.pdf
- https://www.yourarticlelibrary.com/cost-accounting/service-costing/the-beginners-guide-to-service-costing/55962
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