Austria's decision to start inspecting trucks at its border with Hungary after 71 migrants died in a food truck has created a huge, 25-kilometer (15 1/2-mile) traffic jam on the main Budapest-Vienna highway.

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.