Researchers say more must be done to determine why people react aggressively on the roads.

Road officials say ongoing construction on the country's major routes has prompted motorists to abuse workers both verbally and physically.

The first phase of the Gauteng Freeway Improvement Project is only expected to be completed by the end of next year.

It is causing congestion and frustration on many of the province's roads.

Researcher Nicola Taylor said there could be a number of reasons why motorists behaved the way they do.

"It could be a number of aspects from a psychological point of view. It would be personality thing and an inability to deal with anger."