Commuter frustration as road speeds plunge across Brisbane

Brisbane commuters are spending longer behind the wheel as average speeds plummet on the city's roads.

The average speed for commuters dropped below 40km/h during the first six months of this year, with the morning peak sitting at only 35km/h.

That marks a drop from 42km/h a year prior for the same period.

Stanley Street in South Brisbane is the slowest major road, with drivers forced to travel at 16km/h on average.

Brisbane City Council recently installed almost 50 new traffic lights over a four-year period.

Lord Mayor Graham Quirk said average speeds nevertheless had only dropped one km/h on council-owned roads in the past year, despite major works.