In times of high pollution events a "smog alert" (Szmogriadó) can be activated in Budapest. Cars that don't meet the minimum standard Euro 5 are not allowed to circulate between 06:00 and 22:00.
During the smog alert the owners of the banned vehicles can use public transport for free. They should be prepared to show their car documents.
This imply that most efficient vehicles and Evs are allowed to circulate in the city during the Szmogriadó.
Similar measures exist in other Hungarian cities.