The aim of this study was to investigate the development of traffic safety on Highway 1 before and after the construction of the motorway on the study segment between Turku and Lohja in the principality of Uusimaa, Finland. The study was based on accident data, data from the state road register, as well as a site visit.

The status of safety performance on Highway 1 is good, and traffic safety risks along this corridor are low. Traffic levels have increased significantly after recent major reconstruction of the highway. Accidents involving personal injury on Highway 1 have fallen by 60 - 80 % after the reconstruction of the highway. The most common types of accidents, including personal injury accidents, on the highway were single accidents and rear-end collisions. Of personal injury accidents, 60 % are due to driving off the road. No collisions were involved with personal injury accidents between 2007– 2011; however, fatalities due to driving the wrong way on the highway were previously classified as a common type of accident on highways.

On the basis of the performed analysis of accidents and road visits, it can be concluded that the safety performance can and should still be improved, especially on the old highway routes. Individual accidents can be better prevented and the effects mitigated significantly by improving and developing traffic conditions. Still, not all accidents can be prevented by technical measures or improvements to the traffic system.

Deficiencies were noted during site visits and suggestions for improvements were provided to authorities in Southwest Finland. Special attention was paid to improving crashworthiness and preventing driving in the wrong direction on entry and exit ramps. Proposed impro­vements include lowering shrubbery and installing additional guard rails at critical locations. In certain locations, improving embankment crashworthiness can be used as an alternative to building multiple barriers. Wrong way signage can be installed at locations where ve­hicles are found to enter ramps against the normal traffic direction.