State agencies have become increasingly interested in the construction of managed-lane facilities operating concurrently with general purpose lanes along existing roadways as a means of addressing the continued growth of traffic congestion on freeways. Nonbarrier separation techniques to restrict access to managed lanes are gaining in popularity. Such separation methods, however, permit nearly unlimited improper ingress to and egress from the managed lanes, affecting free-flow speeds, safety, and revenues. Even with significant enforcement, violation rates related to non-barrier-separated managed lanes in the United States are considerable. Despite this, such violation behavior has not been incorporated into any model developed to predict improvements in traffic performance metrics and the potential revenue that can be raised through the introduction of a new high-occupancy toll (HOT) lane facility within an existing roadway or to assess potential practicable operational strategies and facility designs. Nor has any prior study systematically considered the impact of violation on the performance of these facilities. This paper seeks to assess the importance of this omission. Results of this study indicate that vehicles whose drivers choose to violate restrictions on the studied non-barrier-separated, limited-access HOT lane facility significantly affect roadway facility performance estimates when violation rates reach 10% of roadway users or higher.