Single-vehicle run-off-the-road crashes result in about one-third of all highway fatalities and one-half million people injured annually, with a societal cost of $80 billion each year. Continuous shoulder rumble strips (CSRS) are one countermeasure used to address this significant safety problem. Data were analyzed for two states (California and Illinois) from the Highway Safety Information System to estimate the safety effects of CSRS on freeways. Before-and-after evaluations of CSRS projects with the use of different comparison groups were conducted. The results from the evaluations indicate that on average CSRS reduce single-vehicle run-off-the-road crashes by 18.3% on all freeways (without regard to urban/rural classification) and by 21.1% on rural freeways. Two types of potential adverse effects related to safety with CSRS were analyzed. The first type pertains to the crash risk that CSRS may present because of driver startle/panic responses. The second potential adverse effect of CSRS is crash migration. The research findings indicate that these potential adverse effects are insignificant.