The Civil Engineering Association in Samoa says the government has failed to implement its recommendations which would have made the driving side switch safer.
From September the 7th motorists in Samoa must drive on the left side of the road instead of the right.
The lobby group, Pass is arguing in the Supreme Court that the change is unconstitutional on safety grounds.
Our correspondent Autagavaia Tipi Autagavaia says the Civil Engineering Association has outlined to the court a report it gave to the government in 2007.
He says the association's vice President, Leiataua John Tinai told the court most of the country's roads were built to accommodate left-hand drive vehicles, particularly on bends, and the report recommended that all roads be widened to accommodate the change.
"But none of that has been done, because it's only a very small part of the town area road that is currently under a widening process, but the recommendation is for all roads in the country, including those in the rural villages."
Autagavaia Tipi Autagavaia says the report also highlighted how the cost of the driving switch could run into several millions of dollars.