Bridges are integral to roads in enabling road users to cross natural and man-made obstacles. There are 994 bridges on Estonian national roads as of 01.01.2016. They can be divided in various ways. The simplest and most common way is to group bridges on the basis of their construction type:
a bridge – a construction that is necessary for crossing a body of water;
an overpass – a construction that is necessary for crossing a terrain feature or a man-made obstacle;
a tunnel – a construction that is necessary for passing an obstacle from underneath it.
There are 846 bridges (85.1%), 147 overpasses (14.8%) and 1 tunnel (situated on the 33.7 km of the Tallinn - Tartu - Võru - Luhamaa road) on Estonian national roads. In the context of this text, all constructions are regarded as bridges.
From the road user’s viewpoint, the most important division basis is the road length necessary for crossing an obstacle. On the basis of length*, bridges are divided as follows:
a short bridge (3-25 m);
an average bridge (25-100 m);
a long bridge (over 100 m).
* length is defined as the distance between the rear walls of abutments across the axis of the road.
The majority, or 703 of the bridges on our national roads are short bridges (70.7%), there are 273 average length bridges (27.5%) and 18 long bridges (1.8%) on national roads. The average length of bridges on national roads is 22.8 m and the total length of said bridges is 22,673.2 m.
The longest bridge is the Variku overpass (with a length of 420.8 m), which is situated on the 186.1 kilometre of the Tallinn - Tartu - Võru - Luhamaa road.
The bridges can be divided into groups based on the main construction material used:
concrete (reinforced concrete and prestressed concrete);
metal (iron, steel and cast iron);
masonry (quarry stone and limestone);
timber (laminated timber).
The majority, or 786 of the bridges on our national roads are made of concrete (79.1%), there are 182 (18.3%) metal bridges, 18 (1.8%) masonry bridges and 8 (0.8%) timber bridges on national roads.
In addition to technical aspects, bridge can also be grouped on the basis of their age (see Graph 1). About half of the bridges on national roads were built during the period of 1950-1980. The average age of the bridges is 41 years.