The Zilov Gap was a 400 mile (640 km) roadless section in Central Siberia where, before the completion of the Chita-Khabarovsk highway (M58), there was no east-west road - the only communication was via the Trans-Siberian Railway.
The Zilov Gap was notorious for the muddy terrain during the rasputitsa, where 300 metres progress could take 3 hours and its numerous serious river crossings; it posed a major challenge to long-distance overland expeditions and nearly caused the end of the Mondo Enduro expedition; the Long Way Round trip avoided it altogether.
There is a well established road route round the north of Lake Baikal which follows the Baikal Amur Mainline line.
There is a new road from Khabarovsk to Chita which was under construction in 2005, see article (with link to map in Russian) and photos. The remaining 2 km gap on the southern route was about to be filled in. The road was then used to export used cars from Japan.
Eastbound travellers on M58 highway would load their cars onto cars of the Trans-Siberian Railroad at Chernyshevsk for the 800-km trip to Magdagachi (at least this was the case in 2001.). The Chernyshevsk-Magdachi gap is just north of the northernmost part of Manchuria.