Migrants are processed at the intake area of the Department of Homeland Security holding facility, in Texas. March 30, 2021.

Publication Type

The effect of lawful crossing on unlawful crossing at the US southwest border

Working Papers 24-10
Photo Credit: Dario Lopez-Mills/Pool via REUTERS


Technical Summary

Legal and illegal markets often coexist. In theory, marginal legalization can either substitute for the remaining parallel market, or complement it via scale effects. This paper studies migrants crossing without prior authorization at the US southwest border, where large-scale unlawful crossing coexists with substantial, varying, and policy-constrained lawful crossing. The paper tests whether lawful and unlawful crossing are gross substitutes or complements, using lag-augmented local projections to analyze a monthly time-series on the full universe of 10,658,497 inadmissible migrants encountered from October 2011 through July 2023. Expanded lawful crossings cause reduced unlawful crossings, an effect that grows over time and reaches elasticity –0.3 after approximately 10 months. That is, in this case, expanded activity on the lawful market substitutes for the parallel market, even net of scale effects. This deterrent effect explains approximately 9 percent of the overall variance in unlawful crossings. In an ancillary finding, the paper fails to reject a null effect of depenalizing unlawful crossings on future attempted unlawful crossings.

Plain Language Summary

An increasing number of migrants attempt to cross the US Southwest border without obtaining a visa or any other prior authorization. 2.5 million migrants did so in 2023. In recent years, responding to this influx, US officials have expanded lawful channels for a limited number of these migrants to cross the border, but only at official ports of entry. These expanded lawful channels were intended to divert migrants away from crossing between ports of entry, by foot or across rivers, thereby reducing unlawful crossings. On the other hand, some have argued that expanding lawful entry would encourage more migrants to cross unlawfully. This study seeks to shed light on that debate by assessing the net effect of lawful channels on unlawful crossings. It considers almost 11 million migrants (men, women, and children) encountered at the border crossing the border without prior permission or authorization. Using statistical methods designed to distinguish causation from simple correlation, it finds that a policy of expanding lawful channels to cross the border by 10 percent in a given month causes a net reduction of about 3 percent in unlawful crossings several months later. Fluctuations in the constraints on lawful crossings can explain roughly 9 percent of the month-to-month variation in unlawful crossings. The data thus suggest that policies expanding access to lawful crossing can serve as a partial but substantial deterrent to unlawful crossing and that expanding access can serve as an important tool for more secure and regulated borders.

Data Disclosure:

The data underlying this analysis can be downloaded here [zip].

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