Accident Analysis and Prevention 32 (2000) 589 – 599 An expert judgment model applied to estimating the safety effect of a bicycle facility Lars Leden a,b , Per Ga ˚rder c, * , Urho Pulkkinen d a Lulea ˚ Uniersity of Technology, SE-971 87 Lulea ˚ , Sweden b VTT Communities and Infrastructure, P.O. Box 1901, FIN-02044 VTT, Finland c Department of Ciil and Enironmental Engineering, Uniersity of Maine, Orono, ME 04469 -5711, USA d VTT Automation, Industrial Automation, P.O. Box 1301, FIN-02044 VTT, Finland Received 19 July 1998; received in revised form 29 June 1999; accepted 1 July 1999 Abstract This paper presents a risk index model that can be used for assessing the safety effect of countermeasures. The model estimates risk in a multiplicative way, which makes it possible to analyze the impact of different factors separately. Expert judgments are incorporated through a Bayesian error model. The variance of the risk estimate is determined by Monte-Carlo simulation. The model was applied to assess the safety effect of a new design of a bicycle crossing. The intent was to gain safety by raising the crossings to reduce vehicle speeds and by making the crossings more visible by painting them in a bright color. Before the implementations, bicyclists were riding on bicycle crossings of conventional Swedish type, i.e. similar to crosswalks but delineated by white squares rather than solid lines or zebra markings. Automobile speeds were reduced as anticipated. However, it seems as if the positive effect of this was more or less canceled out by increased bicycle speeds. The safety per bicyclist was still improved by approximately 20%. This improvement was primarily caused by an increase in bicycle flow, since the data show that more bicyclists at a given location seem to benefit their safety. The increase in bicycle flow was probably caused by the new layout of the crossings since bicyclists perceived them as safer and causing less delay. Some future development work is suggested. Pros and cons with the used methodology are discussed. The most crucial parameter to be added is probably a model describing the interaction between motorists and bicyclists, for example, how risk is influenced by the lateral position of the bicyclist in relation to the motorist. It is concluded that the interaction seems to be optimal when both groups share the roadway. © 2000 Elsevier Science Ltd. All rights reserved. Keywords: Expert; Model; Safety; Bicyclist; Raised crossing www.elsevier.com/locate/aap 1. Purpose and methods The primary purpose of this study has been to de- velop a model for estimating the changes in risk of modifications to the geometrical layout of streets. The model consists of three submodels: a risk index model, an expert assessment model and a risk attribute model. The model is here applied to the safety of bicyclists. A reason for this application is that bicyclists have more injury accidents per kilometer traveled than almost all other road-user categories (Ga ˚rder, 1994). On the other hand, bicycling is an environmentally friendly mode with health benefits to the rider as long as he or she is not injured in an accident. According to Carre ´ (1997) the health aspects are 5–10 times more important than the safety aspects. Still, it is important to improve the safety of bicycling. One way of doing this is to improve the physical environment, including creating safe cross- ing points between bicycle paths and streets. This paper deals with how to evaluate the safety effect of the construction of such a path. 1.1. Surey An 11-page survey was developed. It starts out de- scribing a situation with an adult bicyclist riding on a bike path along an arterial. A motorist approaches him from behind. The inattentive motorist is turning right * Corresponding author. Tel.: +1-207-5812177; fax: +1-207- 5813888. E-mail address: garder@maine.maine.edu (P. Ga ˚rder) 0001-4575/00/$ - see front matter © 2000 Elsevier Science Ltd. All rights reserved. PII:S0001-4575(99)00090-1