[laluks]

From Vandiperiyar it is 24km, not from kumily. You have to turn left if coming from Kumily at a junction called Kakki kavala.

Till Gavi any cars can go no issues. narrow roads, and some potholes.

Permission - Yes it is required theoretically.
You must be staying at the gavi eco resort, or you must be having a day programme with them for easy permits.

But some people just drive through with some arrangements.

I had taken the gavi route from Vandiperiyaar and exited through Angamoozhy to Pampa with my Civic in September 10. I had taken a guide from Gavi with me throughout the trip for access and safety. I have passed through heavily protected power projects area. Kakki Dam, Pampa Dam, Seethathode, plappally before reaching Pampa on the foothills of Sabarimala. I'll put up that details in my log sometimes. Advise not to take sedans, but if you are a serious driver nothing stops you.