As congestion on two-lane rural roads increases, there is increasing interest in conversion to a four-lane divided facility within the same corridor. The authors have attempted to estimate the benefits of such conversions by developing cross-sectional models producing crash rates for typical sections of two- and four-lane roadways in California, Michigan, North Carolina, and Washington. Predicted crash reductions for conversion from most typical two- to four-lane divided sections ranged from 40-60 percent. The reduction due to conversion to a four-lane undivided configuration is much less well defined, ranging from a 20 percent reduction to a slight increase. Future research needs include (a) verification of the undivided four-lane results, (b) additional information on the effects of driveways, (c) estimates for higher levels of two-lane average daily traffic, (d) expansion of the outcome variable to include crash severity, and (e) verification of all results by before-and-after studies of actual conversions.