At the U.S.-Canadian border, rising truck volumes are a welcome sign of economic improvement. But an 8 percent increase in truck crossings in Detroit in the first quarter also raises concerns about the speed and fluidity of cross-border freight traffic.

“We do a preponderance of our crossings in Windsor, where’s there’s one bridge,” said Scott Dobak, president of trucking operator Dicom Transportation Group, Montreal, which owns Canadian and U.S. motor