Why a ministerial disagreement over curb weight matters for India's fuel efficiency standards


Recently, there has been a disagreement between the two ministries concerned with development of passenger vehicle fuel efficiency standards in India. The disagreement pertains to the assumption over how much passenger vehicles in India might weigh in 2021, when the fuel efficiency standards are fully phased in. On one hand, the Minister of Heavy Industries, Mr. Praful Patel, was quoted as saying that the assumed average curb weight of car should be maintained at 1,035 kg in 2021. (Curb weight, or “unladen mass,” means the mass of the vehicle in running order without crew, passengers, or load, but with the fuel tank 90% full and the usual set of tools and spare wheel on board, where applicable.) However, the Bureau of Energy Efficiency (BEE) has assumed that average curb weight will increase to 1,145 kg by 2021.

Why does this assumption matter to the efficacy of fuel efficiency standards in India? As the figure below shows, a vehicle efficiency standard targeting fleet average CO2 emissions of 113 gCO2/km at 1,145 kg is about 5gCO2/km stricter for the standard that achieves 113 gCO2/km at 1,035 kg. In other words, if the average mass of vehicles in India ends up at 1,145 kg, but regulations are developed with the assumption for 113 gCO2/km (4.84 l/100km) at 1,035 kg, then the resulting standard would actually be 118 gCO2/km (5.05 l/100km). Over the 150,000km of useful vehicle life, this would translate into an excess of 315 liters of fuel use worth over Rs. 24,000 (US$400) in additional fueling costs!

It appears that the trend over the past six years supports BEE’s estimate—indeed, if anything BEE may have underestimated the average yearly increase in vehicle weight over the past several years. The average curb weight of passenger cars in India has increased about 18 kg per year since fiscal year 2006–2007, as shown in figure below. If this trend continues, then the average vehicle weight will reach 1,145 kg as early as 2016. Even if we assume that the vehicle weight increases at half the rate at just 10 kg per year, average vehicle weight will still reach 1,145 kg by 2018.

There are several reasons for why the average curb weight of India’s passenger vehicle fleet is increasing. One, as I’ve noted before, is the growing market share of larger vehicles (SUV, MPV, minivans). Another is the increasing preference for cars with diesel engines, which are heavier than gasoline engines.

Safety regulations also play a part in this story. With mandatory crash testing established this past year in India, many manufacturers are adding safety features like airbags to their vehicles, which also add weight. Consumers are demanding increasing amount of comfort and entertainment related features, which also tend to affect vehicle weight to an extent.

There are, of course, pushes in the other direction. Lightweight materials offer the potential to reduce vehicle weight significantly. But given that Indian vehicle fuel efficiency standards will be weight-based (as opposed to footprint-based), there will be little incentive for manufacturers to maintain average vehicle curb weight at 1,101 kg.