downstream to the deeper waters of the Firth of Clyde and improvements in engineering technology had allowed the consideration of bridges downstream of the city centre, namely the Kingston Bridge and, much further downstream than the Tunnel, the Erskine Bridge. The tunnels The road tunnels are each 762 metres (2,500 feet) long with a gradient approaching 6% or 1:16. The width of the river at this point is . Each road tunnel carries two lanes of traffic as part of the A739 road, and are completely separate except for a very small crossover passage between the road tunnels at the nadir (barely large enough for a single pedestrian). They are monitored and controlled from the two Portal towers, one at each end of the tunnel, where CCTV monitors the entirety of the tunnel. Beneath the road tunnel decks run foot and cycle tunnels; and below those, the tunnels' services. Pedestrian and cycle tunnels Both tunnels are open to pedestrians in both directions. The eastern tunnel is open to cyclists going southbound, and the western tunnel to cyclists going northbound. In 2008, CCTV secure entry systems were installed at the portals of these tunnels in order to reduce crime and anti-social behaviour in the tunnels. Repair work The estimate for traffic levels in the tunnel was between 9,000 and 13,000 vehicles per day during construction; on the first day of opening, 22,000 vehicles used the tunnel. Current estimates for traffic levels are around 65,000 vehicles per day. These unanticipated high volumes of traffic have increased the wear rate for the tunnel, causing it to close repeatedly for repair and renovation work, which has disrupted traffic in the area for over a decade, and has arguably led to the increase in traffic causing similar problems on the Kingston Bridge. The more recent repairs, costing as much as the initial outlay for construction, involved installing a second, modern, fireproof layer, enabling the tunnel to meet European safety standards after St Gotthard and Mont Blanc tunnel fires, along with new air extraction systems and new lighting. Work began in March 2005 and was scheduled to last until at least April 2006, with one of the tunnels closed during off-peak hours (19:00 to 07:00 daily). However, problems that were encountered meant the work was only completed in 2010. The roadworks coincided with the "Hold Your Breath" project which aimed to add an artistic experience to