CHENNAI: With the trial run of 22 Compressed Natural Gas (CNG) buses across eight transport corporations yielding significant cost savings and enhanced mileage for the state transport undertakings (STUs), the transport department has decided to convert 1,000 diesel buses to CNG across the state. Tenders have been invited for this initiative, according to sources.
The number of buses allocated for conversion for each transport undertaking has not been finalised yet. Buses aged six to seven years or those with a total running distance of less than eight lakh kilometres will be selected for conversion.
The average cost for converting a diesel bus to CNG has been set at Rs 7 lakh. While mofussil buses recover conversion expenses in nine to 10 months, town buses will require 12 to 13 months. As per official sources, buses undergoing conversion should remain operational for the next five to seven years.
T Prabhushankar, managing director of Pallavan Transport Consultancy Services (PTCS), the technical arm of the transport department, told TNIE that this initiative aligns with the state government’s commitment to reducing greenhouse gas emissions through programmes like the Tamil Nadu Climate Change Mission.
He highlighted that the Metropolitan Transport Corporation (MTC) has already undertaken environment-friendly initiatives by planning to replace diesel buses with 1,200 electric buses in the coming months. The CNG trial has proven not only cost-effective but also beneficial in increasing mileage.
Prabhushankar added that, apart from CNG, one bus is also being operated on Compressed Biogas (CBG), which can be produced from solid waste. “CBG is much cheaper than CNG. Possibilities to introduce hydrogen buses — a fully-clean energy solution — will also be explored,” he said.
TN has 325 CNG outlets, targets 3,250 by ’26
“Currently, we lack precise data on the reduction in emission levels due to the conversion from diesel to CNG,” Prabhushankar added.
Currently, 22 buses have been retrofitted to run on CNG and are already operational. These include four from SETC, two from MTC, and three each from TNSTC divisions in Madurai, Salem, Kumbakonam and Coimbatore, while Tirunelveli and Villupuram have two buses each.
CNG-powered buses, which have been in operation for over six to 12 months now, have shown a 15% increase in mileage compared to those running on high-speed diesel. Data indicates that CNG buses achieve 6.1 to 7.1km per kilogram, while diesel buses manage only 4.21 to 5.96km per litre.
Official sources from PTCS revealed that transport corporations save between Rs 2.72 and Rs 4.76 per km by operating buses on CNG instead of diesel. The per-km savings for CNG buses are Rs 3.2 in Chennai, Rs 5.20 in Kumbakonam and Rs 6 in Salem. The variation in savings is due to the price of CNG, which is Rs 90 per kg in Chennai compared to Rs 70-72 in Nagapattinam and Salem.
This initiative, aimed at reducing greenhouse gas emissions, is funded by the Tamil Nadu Pollution Control Board (TNPCB), Tamil Nadu Innovation Initiatives (TANII) and Tamil Nadu Environmental Impact Assessment Authority, among other agencies.
Sources noted that the union government has set the maximum lifetime of a bus at 15 years. Consequently, the technical committee appointed by the state government has recommended that only buses aged six to seven years or with a running distance of less than 8 lakh kilometres should be selected for conversion.
“CNG companies will not be responsible for maintaining the retrofitted buses. The corporations are equipped to handle their maintenance, so no annual maintenance contract has been assigned for these buses,” an official said.
The state currently has 325 CNG outlets and it has proposed to increase this to 3,250 outlets by the end of 2026. “The transport department will also convert its major diesel depots into CNG stations,” the official added.
CNG buses reduce fuel costs
PTCS revealed that transport corporations save between Rs 2.72 and Rs 4.76 per km by operating buses on CNG instead of diesel. The per-km savings for CNG buses are Rs 3.2 in Chennai, Rs 5.20 in Kumbakonam and Rs 6 in Salem