Chennai: The 263.4km Chennai-Bengaluru expressway is stuck in litigation over a 25-km stretch falling within Tamil Nadu. Karnataka and Andhra Pradesh have already made giant strides in construction of the highway in their respective territories.The 25km stretch from Arakkonam to Kancheepuram of the six-lane NE-7 has seen a mere 50% progress with the contractor going on an appeal against NHAI in Madras high court. Officials said the cases were over, and they were awaiting orders.The problem pertains to high costs of fly ash from Ennore Thermal Power Plant sold by cartels when, according to tenders, the contractor was supposed to get it for free.Besides this stretch, the NHAI has achieved over 90% progress in the 24.5km Walajapet-Arakkonam section, Kancheepuram-Sriperambudur section of 31km, and Walajapet to Guipala.The ₹15,000 crore project was started in 2019, and was supposed to be completed in 2023. It has since missed multiple deadlines.State highways minister Aadhav Arjuna had promised state and national highways contractors that they would not face any hindrance from local cartels blocking raw material. “The highways will procure it for them. NH contractors taking up work for a stretch that is more than 100-km can execute it without hindrance from MLAs or party members,” he told contractors and officials.Nearly 100km of the expressway is open now. Karnataka has opened its entire 71km stretch, while AP has opened a 25km stretch.