Drivers of older diesel-powered trucks are now prohibited from using two road sections in Hamburg, the first German city to implement such a ban.
A German court ruled earlier this year that authorities could ban particularly dirty diesel vehicles as part of measures to limit nitrogen oxide emissions and protect public health.
The case was brought by environmental groups angry at the government's failure to take measures to meet European air pollution limits, and was spurred by revelations about German automakers' cheating on exhaust tests.
The ban in force in Hamburg since Thursday covers two busy roads for a total length of 2.2 kilometers (1.4 miles).
Greenpeace said it hoped Hamburg and other German cities would follow the lead of nearby Copenhagen and Amsterdam in rethinking transportation policy.
