Reassurance is the confidence offered by lighting to walk alone after dark. Lighting that promotes reassurance enhances perceived safety and reduces fear of crime.
Using a qualitative approach we established that the presence of road lighting gives reassurance. This qualitative approach is critical because conventional quantitative methods can falsely lead to this conclusion when it is not intended.
Many field studies have been conducted to compare evaluations of reassurance under different light levels. One limitation of these past studies is that they used category rating, and evaluations using this procedure will be affected by range bias. This would mean that, in any given study, the higher illuminance evaluated will be considered safe and the lower illuminance unsafe, regardless of the illuminances used: field trials using different illuminances will therefore reach conflicting conclusions.
In this article we report an experiment conducted to confirm that reassurance ratings are influenced by range bias.
When responses are given using a rating scale there is a common tendency for responses to converge near the middle of the scale, which may be the case when respondents do no clearly understand the item they are asked to evaluate. In one field study, a central tendency was evident in two-thirds of the 55 evaluations.
The effectiveness of road lighting at promoting reassurance is conventionally measured using surveys carried out after dark. As noted above, this approach does not work. One alternative is the day-dark approach proposed by Boyce et al (2000). Reassurance is evaluated in daytime as well as after dark: good lighting is that which reduces the day-dark difference.
We conducted a reassurance field survey using the day-dark approach.
These results suggested minimum illuminance and/or illuminance uniformity exhibit stronger association with the day-dark difference than does mean illuminance.
To interpret optimal illuminance we targeted a day-dark difference of 1.0 units of the 5-point response scale, this difference being associated with a significant change in walking behaviour (Foster et al 2016). For a day-dark difference of 1.0 units, the results suggest a minimum horizontal illuminance of approximately 1.0 lux.
Foster S, Hooper P, Knuiman M, Christian H, Bull F, Giles-Corti B. Safe RESIDential Environments? A longitudinal analysis of the influence of crime-related safety on walking. International Journal of Behavioral Nutrition and Physical Activity 2016; 13: 22-30.
Fotios S, Liachenko Monteiro A, Uttley J. Evaluation of pedestrian reassurance gained by higher illuminances in residential streets using the day-dark approach. Lighting Research and Technology, 2019; 51(4): 557-575.
If people feel it is safe, they are more likely to walk (or cycle). Pedestrian count data offers an objective alternative to the subjective evaluations of field surveys.
We analysed pedestrian count data from automated counters in a US city. To isolate the effect of light from other parameters (purpose and destination) we compared pedestrian numbers for a certain hour in the few days before and after daylight savings clock change. This hour tended to dark before clock change and to light after clock change (and vice versa) and was compared with control hours (permanently light or dark before and after clock change) using an odds ratio.
The results show significantly fewer people tend to walk when it is dark.
To validate the findings, the pedestrian count data were analysed using an alternative method of analysis which considered pedestrians counts across the whole year rather than just those days near to the clock change.
These results also show that significantly fewer people tend to walk when it is dark.
We are proposing a minimum illuminance of 2.0 lux is sufficient to optimise reassurance in a given location.
Further work is ongoing to test this:
1) Analysis of a study carried out in parallel in Rome. Further data is desirable.
2) By considering alternatives to category rating to characterise reassurance: we have recorded skin conductance response and gaze behaviour and will compare these measures with ratings in the same locations.