The report is an attempt to describe the effects on accidents of compulsory use of running lights - low beam or special lamps - during daylight in Sweden.

The study is carried out on police reported traffic accidents with personal injury in Sweden. The before and after periods are two years before and two years after the operative day of the law, October 1st 1977.

The use of running lights in the before-period was roughly speaking 50 % and in the after-period over 95 %.

The basic assumption is that the use of running lights in daylight influences multiple accidents in daylight and only those. The method used is to study the relation of daylight to darkness numbers of multiple accidents. The corresponding relation for single vehicle accidents is taken as control.

The estimated total effect depends both on the subdivision of accident data and the method used for accidents with unprotected road users. The estimates vary from 6 to 13 % reduction - from the before-period to the after period - of multiple accidents during daylight or 450 to 1100 less police reported accidents with personal injury per year. The estimated effects are not significant on a 5 % level.

Undersökningens syfte har varit att utifrån den finska trafikolycksstatistiken belysa effekten av tänd fordonsbelysning under dagsljusförhållanden - s k varselljus - på trafikolyckor.

Att den finska trafikolycksstatistiken avseende polisrapporterade olyckor på det statliga vägnätet skulle kunna belysa denna trafiksäkerhetsåtgärd hänger samman med att olika åtgärder vidtagits för att öka användningen av varselljus utanför tätort under vinterperioden i Finland och att dessa åtgärder givit upphov till en mycket hög användningsfrekvens.

Sammanfattningsvis kan konstateras att även om andra vidtagna säkerhetsåtgärder och variationer i yttre för hållanden försvårar analysen av varselljusanvändningens effekt på olyckor så utgör resultaten från den finska trafikolycksstatistiken en mycket stark indikation på att användningen av varselljus har en betydande olycksreducerande effekt.

The purpose of the study has been to investigate, on the basis of Finnish statistics, the effect of daytime vehicle lighting, "running lights", on road accidents.

The relevance to this road safety precaution of Finnish figures concerning accidents occuring on the national road network and reported to the police is connected with the fact that various measures have been taken to increase the use of running lights in Finland outside urban areas during the winter period and that these measures have resulted in a very high frequency of use.

The conclusion is that although the analysis of the effect on accidents of the use of running lights is hampered by other precautions and by variations in external conditions, the results obtained from the Finnish statistics strongly indicate that the use of running lights do a great deal to reduce accidents.