Seaward Street Interchange

Seaward Street Interchange forms part of junction 21 of the M8. The junction as a whole is somewhat more complex, comprising 2 eastbound offslips and 2 westbound onslips. Only one of these pairs meets the Seaward Street roundabout, which lies underneath the Scotland Street Viaduct. Even more confusing is that none of these sliproads meet the M8 itself, instead they all connect with the outer carriageways, which are generally considered to be the western end of the M74 since its extension. The junction also includes a u-turn ramp to allow traffic to turn between the M8 from the west to the M77 to the south and vice versa without stopping.

Seaward Street

The roundabout for Seaward Street sits underneath the Scotland Street Viaduct, a vast concrete construction comprising four parallel bridges supporting four separate carriageways. All of these were constructed when the motorway originally opened, with the outer carriageways originating as the eastern sliproads of J21. The roundabout passes under two of the spans, the supporting columns lying on one side of what is a long, narrow island, largely delineated by paint with flat kerbs. The western side of the roundabout is up against the columns, while the eastern side passes more centrally through its span. This is to provide room for the u-turn ramp (see below). The two sliproads climbs westwards to meet the outsides of the outer carriageways some distance before they merge into the mainline of the M8 at J22.

Kingston

The eastern sliproads extend into the Kingston / Tradeston district of Glasgow, and compliment the north facing slips of J20 which allow traffic from the same area to cross the Clyde on the Kingston Bridge. However, these four sliproads all meet the streets in different places, and were built with grander, unrealised, schemes in mind. The offslip from J21 (which is now signed as part of J1 on the M74) turns north to meet the A8, Paisley Road, at a signalised crossroads, while the onslip begins on the one way system of Carnoustie Street / Dalintober Street, with a more convoluted route from the A8. The new onslip for the M74 at J1 starts in much the same place, although only connects to Dalintober Street.

U-turn ramp

When the M77 was originally built, it was a very short spur connecting to the B768 at Dumbreck Road. As the B768 could be reached with minimal difficulty from J24 of the M8, it was considered unnecessary to provide any connection between the M77 and western M8. With the extension of the M77 to the south, this increasingly became a problem, with traffic having to navigate surface streets and traffic signals to make the turn. As a result, a fairly simple solution was implemented in advance of the M74 extension being started. This involved squeezing a single lane U turn ramp underneath the Scotland Street Viaduct, alongside the Seaward Street Roundabout. Because of the way that the outside carriageways work between J22 and J21, traffic from both the M8 and M77 is able to use this ramp to make the U turn and double back onto the other motorway. The surprise, considering the problems that the ramp was designed to replace, is that a single lane appears to be sufficient the majority of the time.

Routes

Route	To	Notes
M8	Clyde Tunnel, Glasgow Airport, Greenock, Paisley, Kilmarnock (M77)
M74	Carlisle
	Kinning Park (North), Gorbals, Govan	Seaward Street northwards
	Kinning Parkway Industrial Estate	Seaward Street southwards
	Kinning Park (South), Park & Ride Shields Road Station, Pollokshields, Gorbals, Scotland Street School Museum	Scotland Street