a 2018 study found that undocumented immigration to the united states did not increase violent crime rates. a 2017 study found that "increased undocumented immigration was significantly associated with reductions in drug arrests, drug overdose deaths, and dui arrests, net of other factors." a 2017 study found that california's extension of driving licenses to unauthorized immigrants "did not increase the total number of accidents or the occurrence of fatal accidents, but it did reduce the likelihood of hit and run accidents, thereby improving traffic safety and reducing costs for california drivers ... providing unauthorized immigrants with access to driver's licenses can create positive externalities for the communities in which they live."