As you motor down the highway, you could be driving over dozens of underground passages -- called culverts. Those are metal pipes or concrete boxes that carry streams beneath the roadbed. In the Northwest, thousands of these culverts are poorly designed and maintained -- blocking the way for endangered salmon. That’s why Native American tribes have sued Washington State.Reporting for EarthFix, Eilis (eye-LEASH) O’Neill headed out to look at some culverts…