Wachtel, Alan & Lewiston, Diana (1994) Risk Factors for Bicycle-Motor Vehicle Collisions at Intersections. ITE Journal September 1994, pp 30-35

The authors analyzed 4 years of Palo Alto, California, police reports for bicycle accidents from 1985 through 1989. The accident incidence was compared to use levels obtained by counting bicyclists on major arterial streets in May 1987.

Excerpts from "Conclusions" pp 35-36:

Bicyclists traveling against the direction of traffic, whether on the roadway or on the sidewalk, and regardless of age or sex, incur much greater risk than those traveling with traffic (on average 3.6 times greater)....

Bicyclists on a sidewalk or bicycle path incur greater risk than those on a roadway (on average 1.8 times greater), most likely because of blind conflicts at intersections. Wrong-way sidewalk bicyclists are at even greater risk, and sidewalk bicycling appears to increase the incidence of wrong-way travel. ...

Bicycling on the roadway in the same direction as adjacent traffic, whether or not bicycle lanes are designated, is not associated with increase accident risk for any [age or sex] group...

These results suggest that urban roadway design - not only bikeway design - must take into account that intersections, construed broadly [to include driveways] are the major point of conflict between bicycles and motor vehicles. Separation of bicycles and motor vehicles leads to blind conflicts at these intersections. It also encourages wrong-way travel, both on sidewalks or paths and on the roadway at either end, further increasing conflicts. Shared use of the roadway in the same direction of travel leads to fewer conflicts and fewer accidents.

Thus the aim of a well-designed roadway system should be to integrate bicycles and motor vehicles according to the well-established and effective principles of traffic law and engineering, not to separate them....

The goal of integration can be promoted through the use of wide, smooth outside lanes that encourage bicyclists to travel on the roadway rather than on an adjacent sidewalk or path....

Sidewalk bicycling adjacent to busy streets with many intersections presents special dangers and should not be encouraged through the construction or designation of bicycle paths parallel to the street...

Sidewalk bicycling is common in residential areas by young children too inexperienced to ride in the street. Since traffic speeds and volumes tend to be lower on these streets and residential driveways are much less busy than business driveways, potential conflicts are reduced, but they are not eliminated. ...