More than 50 per cent of the autorickshaws on city roads and around 60 per cent of those operating in the metropolitan belt are unregistered.

Metro collated these numbers with data gathered from the Regional Transport Authorities (RTAs) in the districts and the all-powerful autorickshaw unions.

According to the rulebook, autorickshaws should be registered with the RTAs in the districts and the Public Vehicles Department (PVD) in the city proper, and ply only on defined routes. Not being registered means an autorickshaw does not have valid vehicle papers, a route permit or both.

“Registration is possible only if vehicles have valid papers. But in most cases, autorickshaws do not have papers and that is why they do not apply for registration,” said a senior traffic department official.

The problem does not end there. These autorickshaws use adulterated fuel, or katatel, and break traffic rules wherever they go. The Telegraph has been running a campaign against three-wheelers using adulterated fuel and poisoning the air.

The additional commissioner of traffic police, K. Harirajan, said a crackdown on illegal autorickshaws had begun. “We have started a joint drive with the PVD to catch illegal autos on the road and have impounded 24 vehicles in the first couple of days.”

According to transport department officials, most autorickshaws in Calcutta are either polluting engines banned in other metros or “replacement vehicles”, the term for three-wheelers that share the registration numbers of old vehicles that continue to be on the road.

“A couple of weeks ago, Baguiati police station referred two autos plying in the area to us because both had the same registration number. We discovered that both were illegal and that a third auto with the same number — the original one — was plying on the Sodepur-Madhyamgram route,” Chapal Banerjee, who heads the Barasat RTA, said.

The fine stipulated by the Motor Vehicles Act for driving an unregistered vehicle is Rs 2,000-Rs 5,000 for the first offence and Rs 5,000-Rs 10,000 or/and a year of imprisonment for the next offence. Banerjee cites a manpower shortage — only 10 officials to cover 27 municipalities, from Salt Lake to Bongaon and Kanchrapara to Sandeshkhali — and police officials point to political patronage of the autorickshaw lobby for not enforcing the law.

“We know that the major proportion of autorickshaws plying in Calcutta and in its fringes are illegal and most are affiliated to Citu unions,” said Tapan Augusti, the general secretary of state Trinamul Trade Union Congress.

Citu leaders claim the police are soft on offenders. “We have repeatedly asked the police to take action against illegal autorickshaws but they have hardly done so,” said Barun Ghatak, the president of the Citu-controlled autorickshaw union.