Five people who were in this truck died when the vehicle hit a backhoe near Cardston, Alta., and overturned into a ditch. (CBC)

Alberta highways have claimed 28 lives in vehicle crashes so far this month — including 13 in the past three days, said the RCMP.

Several members of three different families died in Alberta highway collisions this week. Police believe alcohol or drugs was a factor in each of them.

Four people from the same family were killed Thursday night in a head-on crash near Bonnyville, northeast of Edmonton.

On Wednesday afternoon, five people — including three children — died when the pickup truck they were riding in near Cardston hit a backhoe and overturned into a ditch.

The pickup driver and his three children — aged 9, 6 and 1 — were killed, as well as an adult male passenger.

Three members of another family died Tuesday evening in a multi-vehicle crash south of Leduc, near Edmonton.

Alcohol or drugs are being investigated as factors in 15 of the 28 fatal crashes recorded by the RCMP in Alberta this month.

The force's statistics, which do not include numbers from Alberta municipal police services, indicate that driving offences related to alcohol or drugs are not declining:

• 2009: 3,504 offences year to date.
• 2008: 7,261 offences.
• 2007: 6,999 offences.

"That's a very big disappointment for us simply because we've been working for years and years on public education that says that impaired driving is a criminal offence, as well as it's an offence that people can go out and kill other people by doing it," said RCMP Sgt. Patrick Webb.

While traffic increases in the summer, so does the number of serious vehicle collisions, he added.