Why India skipped BS5 and jumped straight from BS4 to BS6

Why there is no BS5

Indian buyers often ask why their car's emission sticker jumps from BS4 to BS6 with no BS5 in between. There was never a BS5 rule on the road. The government decided in a meeting chaired by road transport minister Nitin Gadkari, with the petroleum, environment and heavy industries ministries, that India would skip the stage entirely and go straight to BS6 by April 2020, as reported by Down To Earth from that announcement.

Petroleum minister Dharmendra Pradhan's reasoning, on record at the time, was blunt: refining BS5 grade fuel and refining BS6 grade fuel cost refiners almost the same amount, so there was no point building an interim fuel standard that would be scrapped within a few years anyway.

What changed in the fuel, not just the engine

The number that actually moved was sulphur. Diesel and petrol under BS4 were capped at 50 parts per million of sulphur. BS6 fuel cuts that to 10 ppm, a tenth of the limit, which is what lets a BS6 engine's catalytic converter and particulate filter survive their rated life without being poisoned by sulphur deposits. Oil refiners spent about ₹80,000 crore nationwide upgrading their plants to make this fuel in time, per the same Down To Earth report. On the vehicle side, Bharat Stage VI also applied particulate matter limits to petrol cars for the first time, not just diesels, and added a particle number limit, both confirmed in the peer reviewed overview of Indian emission standards published on PubMed Central.

The decades it took to get here

Bharat Stage rules did not begin at BS4. India's first mass emission limits came in 1991 for petrol vehicles and 1992 for diesel vehicles, built into the Central Motor Vehicle Rules of 1989, according to SIAM's own technical regulation page. India 2000, roughly equal to Euro 1, followed nationwide in 2000. BS2 reached Delhi, Mumbai, Kolkata and Chennai in 2001. BS3 started in the National Capital Region and eleven other cities in 2005 while the rest of the country ran on BS2. BS4 began in 13 metros in 2010 while everywhere else stayed on BS3, a patchwork that was only meant to end gradually.

It did not end gradually. In its order of 29 March 2017, the Supreme Court banned the sale and registration of all BS3 vehicles nationwide from 1 April 2017, telling manufacturers that public health mattered more than their unsold stock, reported Autocar Professional. That stock ran to roughly 8.24 lakh vehicles worth about ₹12,000 crore, from two wheelers to trucks, and it had to be sold off or scrapped within days. The court effectively forced India's last patchy BS3 to BS4 transition into a single overnight nationwide jump, the same pattern the government then chose deliberately for BS5 to BS6 three years later.

Through all this the actual numbers kept tightening. CPCB's own emission limits for a petrol passenger car show CO falling from 2.72 g/km under India 2000 to 1.0 g/km under BS4, and combined HC plus NOx falling from 0.97 g/km to 0.18 g/km over the same four stages.

A Maruti 800 built in the India 2000 era and a BS6 car on sale today are governed by rules thirty years apart. The gaps in between were never about engineering falling behind. They were about a country deciding, twice, that it was cheaper to leap than to build a bridge.

Sources

• SIAM, emission norms and technical regulation
• CPCB, vehicular exhaust emission standards
• Autocar Professional, Supreme Court bans sale of BS III vehicles from April 1
• Down To Earth, Transport ministry prepones BS-VI implementation
• PMC, An Overview of Vehicular Emission Standards