Journal of Environmental and Public Health a phenomenon that has been observed in certain nonurban areas with a high rate of prescription opioid abuse, for example, Appalachia [20]. These data also have policy implications. In 2008 there were 268,071 OTP patients in the United States [21]. Given that 26% of patients traveled more than 15 miles to attend their OTP, that 6% of patients reside more than 50 miles from their OTP, and that among a subset of 10 OTPs more than 20% of patients traveled across a state border to attend their program, it is important for policy makers and treatment providers to be alert regarding commuting factors. Previous studies with other clinical populations report that distance is negatively associated with health care utilization. Although patients were only surveyed once (at enrollment) it is reasonable to assume that disparities in travel distance are also likely to be associated with treatment retention especially because federal law requires newly enrolled patients to attend the program at least 6 days a week to pick up their medication [22]; opioid-dependent patients who live at a greater distance from an OTP are likely to be at higher risk for dropping out of treatment than patients who live closer to a program. This may be especially evident in rural areas where OTPs are more dispersed, access to drug treatment is less available and underutilized [23], and where treatment continuity is likely to decline compared to treatment continuity in urban areas [24]. It is therefore important that programs respond to these challenges by assuring treatment continuity, such as establishing a more ﬂexible take home policy, mobile methadone maintenance services, and methadone medical maintenance, that is, provision of methadone by an oﬃce-based physician or pharmacy [25, 26]. Eﬀorts should also be made to provide low threshold treatment which may serve to attract and retain patients. Examples could include expansion of buprenorphine within OTPs along with establishing links with oﬃce-based physicians who prescribe buprenorphine. Oﬃce-based buprenorphine treatment is less stringently regulated than medication-assisted treatment provided at an OTP. Another concern is disaster planning. If local programs are wiped out by some natural disaster like hurricane Katrina, plans should be in place to bring mobile treatment to them, to set up programs in other facilities still standing that may not have oﬀered treatment before, and to make sure that programs in neighboring states will promptly take in patients who are evacuated or who choose later on to relocate. Although there are more than 1,200 OTPs throughout the United States it is important to recognize that OTP coverage varies across states [17]. For example, while some states such as New York, California, and North Carolina are relatively well saturated with OTPs (within certain regions), 3 states have no OTPs (North Dakota, South Dakota, and Wyoming), and there are a number of other states with only 1 to 3 operating OTPs, (e.g., Idaho, Mississippi, Montana, and Nebraska). Moreover various states impose moratoriums on the development of new OTPs from time to time and various states are (as of 2010) proposing or have recently passed extremely restrictive legislation with regard to the zoning of OTPs [27]. Despite evidence- based research demonstrating the eﬀectiveness of methadone 9 maintenance treatment [28, 29], expanding access to much- needed services for chronic opioid addiction through the OTPs has still not been realized. One means to address this limitation would be a sustained and national public education campaign about medication-assisted treatment. 4.3. Limitations. Travel distances were estimated based on the center of the ZIP code in which the patient resided and the exact location of the treatment program. If the exact locations of the patients’ residence were known, travel distances could be estimated with greater precision. The straight line distance between the centroid of the patients’ ZIP code to the exact location of the OTP does not capture other factors aﬀecting travel time such as large variability in ZIP code size, road infrastructure, traﬃc, and mode of transportation. Also, travel cost and time may be oﬀset if the treatment program location is close to resources which allow the patient to complete other life tasks such as going to work and shopping [30]. Because OTPs were selected to represent USA regions where prescription opioid use was expected to be prevalent, the sample is not representative of the population of OTP enrollees. Given the prevalence of prescription opioid use in less densely populated USA regions, the central tendency for travel distance observed in this sample may be higher than the central tendency for the population of OTP enrollees. The study did not formally determine the number of OTP enrollees. Therefore it is possible that not all patients who enrolled in an OTP during the study period completed a survey. However, ongoing conversations between the AATOD project director and the OTP liaison indicate that more than 90% of patients completed the survey. We recognize that there were several limitations to this study. However, we feel that it is important to present these results regarding travel distance to OTPs because it likely has a signiﬁcant impact on the quality of life (including treatment retention) among patients. As far as we know this is the ﬁrst study to document OTP travel distance and cross- state commuting across various locations throughout the United States. Further studies such as qualitative studies on how patients cope with long travel distances and longitudinal studies to examine the impact of distance on treatment retention should be conducted. Acknowledgments The study was funded through a subcontract with the Amer- ican Association for the Treatment of Opioid Dependence (AATOD) as part of the Researched Abuse, Diversion and Addiction-Related Surveillance (RADARS) System. AATOD subcontracted with NDRI to perform the study reported here. The authors thank the patients and staﬀ of the opioid treatment programs for participating in the study. References [1] J. E. Billi, C. W. Pai, and D. A. Spahlinger, “The eﬀect of distance to primary care physician on health care utilization and disease burden,” Health Care Management Review, vol. 32, no. 1, pp. 22–29, 2007.