[1] It runs from Tbilisi via Mtskheta, Gori, Khashuri, Zestaponi, Kutaisi, Samtredia, Senaki, Zugdidi, Sukhumi and Gagra to the border with Russia near Leselidze at the northwestern tip of the country, covering in practice 537 kilometres (334 mi).

North of Zugdidi, across the Enguri River which is the disputed Abkhazia–Georgia border, the remaining 198 kilometres (123 mi) of the S1 route through breakaway Abkhazia is not under central Georgian control.

Crossing into Abkhazia from Georgian controlled territory (and vice versa) is not possible by car, only by foot via the Enguri Bridge [ru] which is part of the S1 route.

The road reaches its highest point of 910 m (2,990 ft) above sea level at the southern portal of the Rikoti Tunnel, which opened in 1982.

The redesign of the trunk section of the S1 between Tbilisi and Samtredia to motorway or expressway standards is part of the East-West Highway project, a major investment into Georgia's international road connectivity.

In the 1996 ordinance "Indicators and List for Determination of International, Domestic and Local Roads of Georgia" the S1 route was recorded as the "S1 Tbilisi - Senaki - Leselidze (Russian border)" with an original length of 552 kilometres (343 mi).

In the 1980s expansion of the (then M27) highway to four lanes was envisioned and ground works had already started until Igoeti when the Soviet Union collapsed and Georgia became independent.

This ambitious long term project aims to create a 455 kilometres (283 mi) east-west transport corridor through Georgia and connecting Azerbaijan and Armenia with Turkey by upgrading Georgian sections of the E60 (Poti-Tbilisi-Red Bridge, Azerbaijan) and E70 (Poti-Batumi-Sarpi, Turkey) highways to strengthen Georgia's position as South Caucasus transport hub.

The S1 Kutaisi Bypass was initially constructed as a grade-separated wide two lane highway with hard shoulders, but was doubled to a 2x2 motorway a few years later.

Below a detailed overview of S1 sections that have been or are being upgraded to 2x2 expressway/motorway configuration within the East-West Highway project, in consecutive order from East (Tbilisi) to West.

Starting in Tbilisi the S1 runs north along the right bank of the Kura (Mtkvari) river in a 2x3 lane configuration with a speed limit of 60 km/h (37 mph).

After passing the Saburtalo neighbourhood on the left hand side, the road diverts from the river bank with a wide median and 2x4 lanes.

The road crosses the Kura river and passes Mtskheta, the capital of the Georgian historic Kingdom of Iberia, and Jvari Monastery, the site of Georgia's 4th century Christian conversion.

At Nadarbazevi village the highway runs only a few hundred meters away from the de facto administrative boundary line of the breakaway region.

The 50 km to Zestaponi is a curvy 2 lane highway route through lush and thickly forested river gorges with little opportunity to safely pass slower vehicles while running through villages and settlements.

In the eastern (Tbilisi) direction, the road has a 4 km (2.5 mi) passing lane (2+1) for the uphill climb to the Rikoti Tunnel.

West of Zestaponi, at Argveta, the S1 continues as a 2x2 motorway/expressway and enters the West-Georgian Colchis Plain by following the Kvirila river to Kutaisi, Georgia's 3rd largest city and home to the nation's second airport (David the Builder) which serves as tourist and low-cost carrier gateway.

From here the highway runs anti-clockwise around the local Botanical garden, and after crossing the Chkhousi River the road heads straight towards Abkhazia.

On the west side of the Enguri Bridge there is an Abkhaz checkpoint, after which the highway continues to Gali, the center of the Georgian community in Abkhazia.

At Tkhubuni village, 421 kilometres (262 mi) from Tbilisi and the southern terminus of the Sokhumi trolleybus, the Black Sea coast is finally reached.

[48] Plans to build a new bridge were unfolded in 2016,[49] but in 2021 it appeared no compatible designs and other construction estimations were produced by the company that was paid in advance.

[50] The highway continues west skirting the foothills of the Caucasus Mountains, and after reaching its highest point in the Abkhazian section descends back to the coast via a couple of hairpin bends.

The Georgian S1 route reaches its end after 537 kilometres (334 mi) at the Psou River crossing which is the border with the Russian Federation at Leselidze (Gyachrypsh).