When you plan a trip, you want to calculate how long the drive will take you. However, not all miles are created equal because of varying speed limits and traffic conditions. To get a more accurate estimate of your drive time, you need to parse your trip into smaller segments based on how fast you can drive in each segment.
Estimate your speed for each section of road that you will be traveling on. For example, on a 210-mile trip, you might average 20 mph on the first 10 miles to get to the highway, 60 mph for the next 185 miles on the highway and 45 mph on the last 15 miles once you have exited the highway.
Compute the total drive time for each segment by dividing the number of miles in the segment by the average speed for that segment. For example, to go 10 miles at 20 miles per hour, you would divide 10 by 20 to find that segment would take you 0.5 hours. To cover 185 miles at 60 mph, divide 185 by 60 to get 3.08 hours. To cover 15 miles at 45 mph, divide 15 by 45 to get 0.33 hours.
Add the time from each segment to find the total number of hours it would take to drive. Finishing the example, you would add 0.5 to 3.08 to 0.33, thus the 210 miles would take about 3.91 hours, or 3 hours, 55 minutes.