Thirty-seven traffic accidents on Shanghai’s expressways in the first half of this year involved casualties, down 13 percent from the same period last year, Shanghai traffic police said yesterday.

Almost half of them happened at late night or early morning — between 11pm and 5am — and a large number of fatal accidents were caused by trucks.

Most of the accidents involved rear-end collisions, and the major causes were broken-down vehicles or traffic congestion.

In 19 rear-end collisionsduring trafficcongestion, police found the drivers who bumped into other cars didn’t brake in time. This could mean a lack of concentration.

Police said they have been talking to large freight transportation companies about safety rules and asking them to prevent their drivers from driving when they are fatigued.

The G15 and G60 expressways and the Outer Ring Road registered the largest number of traffic accidents in the first half of this year.