The 964-kilometres-long twin-tube tunnel is Kerala's first ever tunnel for road transport.
The twin tunnels are along the Mannuthy-Wadakkanchery stretch on the NH 544 between Thrissur and Palakkad districts.
A high-level team headed by Regional Fire Officer S Sreejith carried out the final round of inspection ahead of the much-delayed opening of the tunnel towards Thrissur for traffic on August 1.
The accident occurred after a goods truck lost control and rammed into two cars and two motorcycles. The truck then hit a mini lorry.
Work on the six-lane highway between Thrissur and Palakkad had resumed last week after being stalled for nearly 18 months.
Vehicles will be allowed through only one lane from January 27 to February 10 and from February 27 to March 10.
A young woman's life could be saved as prompt action by the bus crew helped them to move her to a hospital with the help of the Highway Police.
As many as 223 lives have been lost in road accidents in this area over the last 10 years.
To avoid the Kuthiran area, drivers are nowadays taking a detour from the Palakkad-Kulappully road to enter the Shornur-Perinthalmanna road to eventually reach the state highway in Thrissur through the Cheruthuruthy Chungam locality.
A major accident on the Kuthiran bridge has forced the authorities to open one of the under-construction twin tunnels temporarily to ease a long-winding traffic snarl on a stretch of the national highway.