Updated

The Mexican government said Friday it will tighten inspections and lower maximum allowed weights for freight trucks after protests over a string of deadly accidents involving double-trailer trucks.

Independent truckers partially blocked highways leading into Mexico City on Friday to protest rules allowing extremely heavy and very long trucks, something they say displaces them from hauling jobs and pressures them to overload their own rigs.

"No to the double trailers that cause accidents," read one sign held up by protesting truckers on a highway north of Mexico City.

Mexico currently allows trucks to roam two-lane roads with loads of up to 80 metric tons and lengths exceeding 100 feet, compared to a U.S. limit of is 80,000 pounds (40 tons) on interstate highways.

Overloading and the use of double trailers on secondary roads apparently played a role in two recent road crashes.

On April 13, a semi-truck pulling two trailers of grain allegedly lost its brakes while speeding along a highway west of Mexico City, then the rear trailer broke free and slammed into a bus carrying university students. Five students and a teacher were killed.

And one week ago, a double-trailer truck on a two-lane road in the Gulf coast state of Veracruz also lost its rear trailer, which slammed into a bus carrying farm workers, killing 43 people.

The federal Communications and Transport Department issued a statement Friday saying it is lowering maximum weights by 4.5 tons, and limiting double trailers to 25 kilometer (15.5 mile) runs on secondary roads. At present the double-longs are theoretically limited to wider, main highways, but a special permit has allowed them to complete many journeys on back roads.

The department also said double-trailers will all have to be inspected within two months. The department said it will increase its inspection force by 14 percent and increase weigh-in scales from 63 to 88.

Double trailers will also have to carry proof of the weight of the freight they carry.