Drivers in the United States have been tallying up more miles than the same time in the previous year for 18 straight months, according to the Federal Highway Administration.

In its latest "Travel Trends" report, the FHWA says that buses, trucks, and passenger vehicles in the nation covered 277.3 billion miles in August. This distance marked an increase of 2.3 percent—or 6.3 billion miles—from August 2014. It was the highest count since the FHWA began collecting the data and the greatest year-over-year increase since 2002.

The FHWA also provided an estimate of seasonally adjusted vehicle miles for August, putting it at 263.3 billion miles. This total was a 3.6 percent increase from the previous year, but a 0.4 percent decrease from July 2015.

In the first eight months of the year, drivers traveled an estimated 2.1 trillion miles, or about 70 billion more miles than the cumulative total in the same month in 2014. The moving 12-month total was estimated to be 3.11 trillion miles.

The Northeast region—including the New England states, New Jersey, New York, and Pennsylvania—had the smallest increase in travel. Drivers in these states traveled 41.16 billion miles, a year-over-year increase of 2 percent.

In Connecticut, overall travel increased 0.5 percent from 2.8 billion miles in August 2014 to 2.81 billion miles in August 2015. Travel on urban arterial roads in the state went up 0.4 percent, from 1.99 billion miles to 2 billion miles, while travel on rural arterial roads increased 0.9 percent from 187 million miles to 189 million miles.

Rhode Island was one of six states with a year-over-year decrease in travel in August. The overall distance traveled fell 0.6 percent, from 833 million miles to 828 million miles. Though travel on rural arterial roads remained unchanged at 78 million miles, urban arterial traffic fell 0.7 percent from 611 million miles to 607 million miles.

The North Central region, consisting of 12 states ranging from Ohio to North Dakota, had the highest total mileage at 62.4 billion miles. This travel was a 1.5 percent increase from the previous year.

However, three states in this region had a year-over-year decline in travel. This decrease was most pronounced in North Dakota, where overall travel fell 2.8 percent from 905 million miles to 881 million miles. Travel also fell 0.2 percent in Minnesota and 0.1 percent in Iowa.

The largest increase in travel occurred in the South Gulf region, eight states stretching from Texas to Kentucky. The distance traveled in these states was 55.5 billion miles, a 3 percent increase from August 2014.

The 13 states of the Western region had an estimated 61.7 billion miles of travel in total, up 2.2 percent from the previous year. In the South Atlantic region, consisting of eight states and the District of Columbia, travel increased 2.9 percent to 56.5 billion miles.

Hawaii had the most significant year-over-year travel increase for the third month in a row, with travel increasing 9.8 percent from 1.06 billion miles to 1.17 billion miles. New York and Tennessee had the next most significant increases at 4.3 percent each, rising to 13.34 billion miles in New York and 6.3 billion miles in Tennessee.

The monthly Travel Trends reports are based on hourly traffic count data from about 5,000 monitoring stations located across the United States. These stations estimate the change in traffic on a road as compared to the same month in the previous year. The FHWA says that due to the limited sample size, a more accurate travel estimate is provided with the annual Highway Performance Monitoring System.