As the width of the lane increases for a section, people can also be expected to drive faster. This has a tendency to increase accident probability. Drivers may also sense the reduced lane width and thus reduce their speeds. Drivers are lulled into a false sense of security by the increased shoulder width and tend to increase speeds and exhibit unsafe driving behavior. Substandard shoulders have a positive correlation with the number of accidents that occur on any given section of highway.
Drivers have less room to take corrective actions after making an errant maneuver.
It is also apparent that drivers are more apt to encounter roadside obstacles with the reduced widths, as these are often the reason that reduced widths are necessary. Substandard left shoulders tend to increase the accident probability for principal arterials and collectors. Curves with more space between them tend to increase the accident probability. Sharp curves with more space between them tend to increase the accident probability. A smaller radius creates a sharper curve, which results in greater potential for driver error.