The Hungarian traffic firm Utinform reported the backup at the Hegyeshalom border crossing Monday and said traffic was slower than usual at other Hungary-Austria border crossings.
Both countries are part of the European Union's Schengen zone of passport-free travel. Under normal circumstances, vehicles are rarely inspected at the border anymore.
Austrian police say the 71 migrants likely suffocated to death in a truck with Hungarian license plates abandoned last week in Austria on the Budapest-Vienna highway. Five suspected human traffickers have been detained in the case and Hungary is stepping up its arrests of smugglers.