Shaped like an arch, the road is 46 kilometres (29 mi) long, of which only a very small fraction passes within the borders of Helsinki itself.

The most recent construction work has been extensive renovation on its busiest stretch in Vantaa, where several interchanges have been built or improved, and lanes added.

Kehä III is often informally or jokingly considered the outer border of the Helsinki area, because most of the urban development of the capital region is inside the ring.

The amount of traffic grew considerably over time and as a result the original intersections with Helsinki's exit roads became dangerous.

At the start of the 2000s, major improvements were made to the heavily used stretch from Tikkurila to Helsinki-Vantaa Airport: the road was widened to 6 lanes and Tuusulanväylä motorway's intersection was rebuilt as a large system connection.