If you want to avoid traffic gridlock, it’s best to steer clear of roadways on Friday afternoons.

Data compiled for Governing by traffic research firm Inrix shows Friday afternoons are the worst time of the week to drive in nearly three-quarters of metro areas across the country.

For most cities with already lengthy rush-hour commutes throughout the week, time spent behind the wheel is further prolonged on Fridays.

The Los Angeles metro area, notorious for its backups, recorded the longest Friday afternoon delays of the 100 areas measured. Average Friday commutes for the region were 44 percent longer than without any congestion, compared to about 34 percent more during peak hours Monday through Thursday. That’s enough to add about 13 minutes to a trip taking 30 minutes without traffic.

Similarly, San Francisco motorists sat in traffic an average of 35 percent longer on Friday afternoons, extending a 30-minute trip by more than 10 minutes.

Drivers leaving town after work account for some of the additional traffic, and this is compounded by other individuals taking care of errands before the weekend, said David Schrank, an associate research scientist with the Texas Transportation Institute.

Morning commutes aren’t as bad because motorists usually head straight to work without making stops on the way.

Areas with many workers living far outside a city can experience significant congestion when all flee the office early. Schrank cited Bridgeport, Conn., which recorded the nation’s fifth-longest Friday afternoon delays, as an example.

The presence of different industries within a metro area can also act to push commute delays up or down.

Schrank said traffic patterns often vary based on the employment sector – those working in factories typically arrive earlier while high-tech employees and others may continue to clock in throughout the morning. Many companies now offer employees flexible schedules, with some opting to work longer earlier in the week so they can take off Fridays. Others also allow employees to telecommute.

The Washington, D.C., area's Friday morning commutes are less congested than any other weekday, likely explained by the large number of federal employees who work from home that day. But with many traveling for the weekend, the area’s Friday afternoon commute still ranks among the nation’s worst.

For some cities, the added delay on Fridays may be more noticeable than others. Portland, Ore., had the largest percentage difference in delays of any area measured by Inrix, with a 30-minute trip taking 3 minutes, 13 seconds longer on Fridays than average times recorded for Monday through Thursday rush-hour traffic.

Any added delay is likely less for those avoiding major highways or commuting short distances. For others, it might seem much longer.

“Sitting in traffic always feels longer than it actually is,” said Inrix spokesman Jim Bak.

Bak said the busiest days typically fluctuate between Fridays and Thursdays.

Inrix compiles a massive database of more than 100 million daily reports from mobile navigation applications, GPS systems in commercial and private vehicles and information recorded by road sensors to compute delay estimates.

Data for this report measured one year of recorded travel times from 4 to 7 p.m. through May for all roadways, including arterial and secondary streets, crisscrossing each metropolitan area. Bak said the company’s analytics and arterial data can adjust for cars stopped at traffic lights and other factors.

Schrank, whose group researches traffic congestion, said transportation agencies have shown a greater interest in collecting and monitoring real-time data. Using it to pinpoint problem areas along roadways is much more feasible than expanding capacity at a time when funds are limited.

"The operational treatment and management of facilities are important these days because that’s what agencies can afford to do,” Schrank said.

Transportation agencies typically separate Monday and Friday from other weekdays when predicting traffic patterns.

In some cases, officials might tweak algorithms for freeway ramp meters to account for added traffic on Fridays. Schrank said they could also, for instance, ensure more wrecker services are on call to clear roadways faster.

Along with utilizing the detailed data to address problems, some transportation agencies communicate it to motorists, reducing their likelihood of getting stuck in traffic.

“All of this is really being made possible by changes and improvements in technology,” Schrank said. “Ten years ago, we didn’t have it.”

View additional data on the best days to commute in metro areas.

Click a city on the map to display data for its metro area. Larger makers represent a higher Inrix commute delay index, which refers to the percentage of average additional time added to a Friday commute between 4 and 7 p.m. An index of 20, for example, would mean a trip taking 30 minutes without traffic is delayed six minutes.

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Afternoon Commute Data

A complete list of all metro areas, ranked by Friday afternoon commutes with the longest delays:

Source: INRIX