"We are just wasting more time driving around," said Peter Phibbs, director of the University of Sydney's urban planning research institute, the Henry Halloran Trust. Population growth was the key reason behind the city's worsening traffic gridlock, he said. "Increased demand is not being matched by the supply of road space." Illustration: Rocco Fazzari The most dramatic changes in average peak speed were in Sydney's northern and western suburbs. The largest fall was on the M2 Hills Motorway from North Ryde to Carlingford, where the average afternoon peak hour speed plunged by 25km/h to 46km/h.

The figures illustrate the effect of a $550 million three-year upgrade on the M2. Average peak hour speeds lifted for about six months after the upgrade was completed in August 2013, but have since slumped. Michelle Zeibots, research director in Transport at UTS' Institute for Sustainable Futures, said upgrades tended to deliver only short-term improvements to traffic. "As people are attracted to the network, speeds deteriorate before flattening out, returning to what they were before the new capacity was added," Dr Zeibots said. "We see these patterns after the opening of every new motorway in Sydney."

The M2 Hills Motorway – which costs up to $6.61 for a car or motorcycle – accounts for five of the 10 segments with the largest declines in average speed. NRMA spokesman Peter Khoury said poor communication about construction of the NorthConnex project was contributing to delays on the M2. "No sooner have they finished the M2 upgrade that drivers get hit by NorthConnex construction – and that's a road people are paying to use," Mr Khoury said. Other routes that experienced steep declines in average speed include the M7 Westlink between Eastern Creek and Seven Hills (20km/h slower in the morning) and Windsor Road between Bella Vista and Rouse Hill (18km/h slower in the afternoon).

Many of Sydney's slowest roads have gone from bad to worse, the analysis shows. Average speeds declined on more than 35 of the 60 segments where motorists were travelling at less than half the speed limit in 2013. On the slowest stretch of road – the Princes Highway from Arncliffe to Haymarket through King Street, Newtown – the average morning speed slowed by 3km/h to 10km/h or 25 per cent of the speed limit. Surging house prices have exacerbated congestion because more people are choosing to live further away from work as a way of coping with housing costs, Professor Phibbs says. "More [infrastructure] investment would help but we will never keep up with demand under the current funding and pricing arrangements," he said.

Meanwhile, drivers are spending more of their day stuck in rush hour traffic. The average peak period – defined as the time during which 75 per cent of morning/afternoon traffic volume occurs – increased by 17 minutes in the afternoon and 15 minutes in the morning between 2011 and 2015. Across the network, the average afternoon peak now spans 3.5 hours while the morning peak stands at two hours and 38 minutes.

Robert Haugh, operations manager of Able Liquid Waste, said deteriorating traffic conditions meant his drivers now had to start their shift at 4am. Two years ago, drivers started at 5am. "We get most of our work done before 8am," said Mr Haugh, who co-ordinates a fleet of 12 trucks based at a depot in Clyde. "Before 8am we get two jobs done an hour. After that, it might be one job every one-and-a-half hours. "Our drivers try to avoid the M2. They find it quicker, generally, not to use toll roads these days. It wasn't like that two years ago."

The Fairfax analysis shows average peak hour speeds improved by at least 1km/h on about one-quarter of monitored road segments. The largest improvements were on the M5 and M5 East Motorways between Mascot and Casula, where the average speed rose to 72km/h from 51km/h in 2013 in the afternoon peak and 65km/h from 54km/h in the morning peak. The government has widened this road. Roads Minister Duncan Gay said he was "not surprised Sydney has clogged and congested roads", saying NSW had gone "backwards on building and upgrading" roads for nearly two decades under previous Labor governments. "These congested roads are exactly why we're investing historic levels funding into roads in NSW [$7.5 billion this year alone], getting on with the job of building world-class infrastructure, fixing pinch points and installing new clearways." Travel times were affected by population growth, employment patterns and changes in the number of people who use public transport, an RMS spokesperson said.