This report presents a comprehensive investigation of glare risks for vehicle drivers on

the E4 road between Linköping and Södertälje, specifically caused by train headlights on

the Ostlänken railway in a proposed future expansion.

Based on simulations, empirical studies, applicable regulations, and previous research,

we propose that threshold values for both veiling luminance (LV) and illuminance (E) at

the driver’s eye should be considered when assessing glare risks. As indicative threshold

values, LV < 2 cd/m² in combination with E < 0.3 lx for incidence angles (θ) < 10° are

proposed. In addition, three risk levels have been defined based on the maximum

distance (Dmax) between trains and road vehicles at which glare may cause discomfort or

visual impairment. In the analysis, Dmax = 500 m is used to represent a high risk level,

Dmax = 600 m a low risk level, and Dmax = 800 m a very low risk level. The selected Dmax

levels represent more or less conservative assumptions regarding the distances at which

glare may be considered relevant and potentially constitute a safety concern.

By using light distributions from measured train headlights, we have modelled the

lighting conditions at the driver’s eye for different relative positions between trains and

road vehicles. The analysis shows that the length of glare shielding required to limit glare

to acceptable levels approximately corresponds to the section of the railway over which

train headlights may cause glare. For Dmax = 500 m, slightly more than 4 km of glare

shielding is required, for Dmax = 600 m slightly more than 6 km and for Dmax = 800 m

approximately 9,5 km. Road lighting can reduce the risk of glare but is unlikely to

eliminate the need for glare shielding in the most critical sections.

The assessment of accident risk and glare is based on a review of traffic accidents

involving reported personal injuries associated with glare in the Swedish Transport

Agency’s accident reporting system STRADA for the years 2010–2024, combined with

information from previously conducted questionnaire studies and analyses of accident

statistics. The number of accidents that can be linked to glare is small compared with the

total number of accidents, although some degree of underreporting is likely. Single-

vehicle accidents are the most common accident type, while pedestrian collisions pose

the greatest risk of serious injuries and fatalities.

The project has contributed increased knowledge on when mitigation measures should

be implemented to avoid excessively high glare from oncoming vehicles and support

safer infrastructure design. While the study addresses glare affecting road vehicle

drivers caused by headlights from oncoming trains on adjacent railway lines, parts of

the results may be applicable more generally.