The M50 motorway is a motorway in Ireland running in a C-shaped ring around the north-eastern, northern, western and southern sides of the capital city, Dublin. The northern end of the route is located at the entrance to the Dublin Port Tunnel. Anti-clockwise it heads northwest through the tunnel and then veers west at a junction with the M1 motorway. It crosses the dual West-Link toll bridges over the River Liffey in west Dublin, and forms a loop around the south-east of Dublin to meet the M11 route (running south to Wexford) at Shankill, County Dublin. Between Junctions 3 to 13 the road forms part of European route E01.
The M50 was first proposed in the Dublin Transportation Study of 1971. Construction began on the first part of the M50, the Western Parkway, in 1987.
This section of the M50, between Junctions 6 (Blanchardstown) and 11 (Tallaght), opened to traffic in 1990. This was followed in 1996 by the Northern Cross section between Junctions 6 and 3 and the Southern Cross between Junctions 11 and 13 which opened in 2001. The completed M50 motorway was formally opened on 30 June 2005, and later the Dublin Port Tunnel, which was opened on 20 December 2006, was included as part of the route.
Work commenced in early 2006 on upgrading earlier sections of motorway. Many of the grade-separated signal-controlled roundabout interchanges were replaced with free-flowing junctions and the road from the M1 junction to Sandyford was widened to three lanes in each direction with a fourth auxiliary lane provided between junctions.
The M50 was originally planned to divert traffic travelling on National Primary Routes away from the city (a full bypass of Dublin). Due to urban expansion it now runs through Dublin's suburbs and serves a route for Dublin itself, connecting the suburbs.
Most of these interchanges were subject to high levels of traffic congestion, as was the former toll-plaza north of the West-Link bridge. The busier roundabout junctions were signal-controlled, with tailbacks extending for several kilometres at rush hour. The most infamous was the Red Cow roundabout junction with the N7, formerly dubbed the "Mad Cow Roundabout". As well as being the junction of two of the busiest roads in the State, the Luas tram Red Line from Tallaght to the city centre used to cross two slip roads at-grade, before continuing city-bound in the median of the R110 (formerly N7). As part of the M50 upgrade works (see below), these at-grade crossings were removed, and on December 2008, the completely reconstructed interchange was open. This greatly reduced the congestion at the once-notorious traffic black-spot.
The roundabout at the N3 is also notable as the Royal Canal and the Dublin-Sligo railway line pass through its centre.
The original speed limit on the M50 was 70 mph (112 km/h) with a reduced decimal limit of 100 km/h when all speed limits in the Republic of Ireland became metric in 2005. The Southern Cross Route (the extension from Junction 12 to Junction 14) was given a lower limit of 60 mph (96 km/h) with a decimal limit of 100 km/h after 2005. This was because of its more undulating terrain, tighter and more frequent curves and resulting shorter sight lines. Because of the doubling of the number of running lanes along most of the route, which has shortened sight lines and increased lane changing, and due of the high number of junctions, the entire length of the route has (with the exception of the sections from Junction 1 to Junction 3 and Junction 14 to 17 with a speed limit of 120 km/h) the same speed limit, of 100 km/h, since it was completely upgraded (2006–2010).
The section of the route which was previously the M1 from Junction 1 to Junction 3 (which is now the M50 up to the port tunnel) retains a speed limit of 80 km/h due to the closely packed junctions, and because of the high number and frequency of lane changes that are required among all manner of vehicles depending on their intended route. For example, traffic travelling Southbound on the M50 approaching the Dublin Port Tunnel must cross 2–3 lanes of traffic to avoid its portals. Whilst in the opposite direction, traffic exiting the tunnel must cross 3 lanes to continue on the M50 rather than progress onto the M1.
The cache location offers a perfect view of the route which today flows much better but was the main area of congestion when the toll plaza was in place.
The cache is a 4ml twist top tube, BYOP.