Neutral Bay and beyond upon arrival on the northern side. The bridge originally only had four wider traffic lanes occupying the central space which now has six, as photos taken soon after the opening clearly show. In 1958 tram services across the bridge were withdrawn and the tracks replaced by two extra road lanes; these lanes are now the leftmost southbound lanes on the bridge and are separated from the other six road lanes by a median strip. Lanes 7 and 8 now connect the bridge to the elevated Cahill Expressway that carries traffic to the Eastern Distributor. In 1988, work began to build a tunnel to complement the bridge. It was determined that the bridge could no longer support the increased traffic flow of the 1980s. The Sydney Harbour Tunnel was completed in August 1992 and carries only motor vehicles. The Bradfield Highway is designated as a Travelling Stock Route which means that it is permissible to herd livestock across the bridge, but only between midnight and dawn, and after giving notice of intention to do so. In practice, the last time livestock crossed the bridge was in 1999 for the Gelbvieh Cattle Congress. Tidal flow The bridge is equipped for tidal flow operation, permitting the direction of traffic flow on the bridge to be altered to better suit the morning and evening peak hour traffic patterns. The bridge has eight lanes, numbered one to eight from west to east. Lanes three, four and five are reversible. One and two always flow north. Six, seven, and eight always flow south. The default is four each way. For the morning peak hour, the lane changes on the bridge also require changes to the Warringah Freeway, with its inner western reversible carriageway directing traffic to the bridge lane numbers three and four southbound. Until September 1982, during the evening peak the tidal flow was set as six northbound and two southbound lanes. The bridge has a series of overhead gantries which indicate the direction of flow for each traffic lane. A green arrow pointing down to a traffic lane means the lane is open. A flashing red "X" indicates the lane is closing, but is not yet in use for traffic travelling in the other direction. A static red "X" means the lane is in use for oncoming traffic. This arrangement was introduced in January 1986, replacing a slow operation where