Anybody going out in any city or metro, is assaulted by smoke and exhaust fumes of every sort of motor vehicle. In reducing size, we notice buses and trucks, SUVs, plush sedans, and “commoners’ small cars”, to use the elitist turn of phrase of Mukul Rohatgi representing government, when arguing against Supreme Court’s ban on large diesel SUVs. [Ref.1. #1. Krishnadas Rajagopal; “Govt. bats for big diesel cars, tells SC that they pollute less”; The Hindu; July 5, 2016]. And of course, the small load carriers, autorickshaws and 2-wheelers. Every one of these consumes petrol or diesel as fuel, and generates exhaust gases. Deteriorating air quality, in particular due to vehicle exhaust-gas pollution, has troubled people for decades now. It only seems to be getting worse and its health ill-effects are the subject of public debate and public demand. In Delhi, it has attracted the attention of the Supreme Court.

There is much debate on whether 2-wheelers are more polluting than cars, and whether large high-end cars with expensive emission-control equipment are less polluting than smaller, cheaper cars, though everybody agrees that buses and trucks are the most polluting of all.

There is also much debate on the standards of pollution control or emission norms built into the engines by manufacturers. The confusion in these debates is huge, and the “commoner”, whosoever he/she is, remains in thrall of scientists holding out on which mode of transport is “more polluting”.

The debate on air quality due to motor vehicles needs to shift to “who pollutes more, and how”, rather than which mode of transport pollutes more. It is the absence of this shift which constitutes misleading the public, and it is left to the reader to guess who is doing this, and why.

Vehicles are fitted with engines of sufficient power to do the job for which the vehicle is intended. This power (called brake horsepower or BHP) is not as important as the “capacity” of the engine measured in cubic centimetres (cc). [1,000-cc=1-Litre (L); 1-cc = 1-mL]. This is because different engines with the same capacity may have different BHP depending on design and efficiency factors.

Thus “2-L” inscribed on a vehicle, indicates that the capacity of its engine is 2-Litres or 2,000-cc, representing the volume of fuel-air mix that the engine sucks in, and the exact same volume of exhaust gases which it spews out after the fuel is burnt, for every two revolutions of its 4-stroke engine. An engine with say 800-cc capacity generates 800-cc of exhaust gases for every two revolutions of its engine, and a 100-cc motorbike generates 100-cc. Per se, a higher capacity engine burns more fuel and emits proportionately more exhaust gases.

A more efficient engine will better convert the fuel to mechanical energy and emit less CO2, and a better catalytic converter fitted to the tail pipe can convert more of the toxic pollutants to less toxic form. But the total volume of exhaust gases depends only on engine capacity. Therefore, since fuel consumption causes pollution, “consume more, pollute more; consume less, pollute less” is axiomatic.

But the government told the Supreme Court: “Big diesel cars and SUVs have better emission norms than smaller cars. Just because a car is big and powerful does not mean it is more polluting. Besides, the more expensive a car, say Rs. 75 lakh or Rs. 1.5 crore, the better it is equipped against pollution.” [Ref.1. #1. Krishnadas Rajagopal; “Govt. bats for big diesel cars, tells SC that they pollute less”; The Hindu; July 5, 2016]. This is misleading at best, as the following discussion clarifies.

Let’s begin by noting that it takes essentially the same quantity of fuel to operate a vehicle whether it is full or occupied only by its driver. Considering per capita pollution by the occupants of different vehicles, is more instructive than debating which vehicle is more polluting, since occupancy is a major determinant of the fuel-economy of any vehicle.

Mr Kumar (name changed) lives in Vasant Vihar, and owns a 8-seater 2-L SUV, which gives him 8-km/L of fuel. He drives himself to work, and he consumes fuel @ 125-mL/km. If he had seven others car-pooling with him in the SUV, the per capita fuel consumption would be 125/8=15.6-mL/km, with eight times less per capita pollution.

Mr.Kumar’s neighbour Mr.Das (name changed), drives a car of 800-cc capacity, which gives him 20-km/L (50-mL/km). When he is the sole occupant, he pollutes 2.5 times less than Mr.Kumar. Mr.Das’ son on his 100-cc motorbike gets 90-km/L (consuming 11-mL/km), and if he does not have a pillion rider, his per capita pollution is due to consuming 22mL/km, less than his father and far less than Mr.Kumar in his SUV.

Consider Mr.Kumar’s domestic help Mrs.Roopwati. She travels by bus, which has a seating capacity of 52 and a standing passenger capacity of 24, but when she travels it is “rush-hour” and the bus is packed with about 90 passengers. The bus consumes fuel @ 0.5-L/km, and for every kilometre travelled during rush-hours, each passenger effectively uses 500/90=5.5-mL/km, producing per capita pollution due to burning fuel @ 5.5-mL/km.

Thus, even though the bus is per se more polluting than Mr.Kumar’s SUV, single-occupancy per capita pollution by Mr.Kumar in his SUV is 125/5.5=22 times more polluting than Mrs.Roopwati struggling in a crowded bus. Full occupancy of his SUV would still be about three times more polluting.

The foregoing demonstrates that use of a smaller personal vehicle is per capita less polluting than a larger personal vehicle, and use of a public vehicle is more fuel economic and that much less polluting than a personal vehicle. A vehicle with better emission standards can make only a marginal difference, since the axiom ”consume more, pollute more; consume less, pollute less” holds good.

Finally, consider the traffic congestion, since it leads to slower traffic and more pollution. Mr.Kumar's SUV, like any vehicle, occupies road space both when it moves and when it is parked on the roadside. A DTC bus too occupies road space though only when it is on the move, because it is not parked on the roadside. Nevertheless, the per capita usage of road space has arguments similar to those for fuel consumption, and Mr.Kumar uses much more road space, which is a public good, than Mrs. Roopwati who represents the vast majority of commuting urban poor. Thus, Mrs.Roopwati is far less demanding of civic amenities than Mr.Kumar.

Howsoever high the emission standards of a petrol or diesel vehicle may be, it cannot but emit exhaust gases directly proportional to the fuel which it consumes. Discussing which vehicle is more polluting diverts attention from the more relevant issue of vehicle usage and per capita pollution, to the emission data put out by vehicle manufacturers with the sole aim of selling more personal vehicles (which increase traffic congestion).

The debate of which vehicle is more polluting, being argued by the government-automobile industry nexus before the Supreme Court, needs to be exposed as specious, and not in the public interest. It is people who make pollution by their use of motor vehicles, as shown above by the differences represented by Mr.Kumar, Mr.Das and his son, and Mrs.Roopwati.

The crying need in all cities and metros has always been affordable, regular, reliable public mass transport to replace personal transport on a scheduled, programmatic basis. This will reduce per capita pollution of the entire population. Hopefully the Hon’ble Supreme Court will recognize government’s misleading, manufacturer-friendly arguments and not withdraw the public-friendly ban on SUVs, but issue time-bound orders for more and efficient public transport, so that both pollution and congestion are simultaneously addressed.

Latest News

Major General S.G.VOMBATKERE