How to estimate driving times

How to estimate driving time on a long trip by using a simple formula, taking into account certain variables.

In college, I decided to drive to Arizona for spring break. Break was about 10 days long, so I had to figure out if I'd be able to spend much time there if I drove. I really needed to budget my time. So I carefully calculated the number of miles I'd have to drive, how fast I could drive, how often I'd have to stop for gas, and if I could really do it in one stretch.

I found that I could drive the 1,800 miles in roughly 36 hours""maybe I wouldn't need to get a hotel along the way then. How did I come to this figure?

A good rule of thumb for a long trip, where you are not going to stay overnight anywhere, is that you average about 50 miles per hour, including stops. So if you know pretty close how many miles you're going to be traveling, use the simple formula: number of miles divided by 50. If your trip is 500 miles, it's going to take you about 10 hours to cover that distance.

Road atlases have tiny red and black numbers along the roads. These numbers indicate miles between towns or highway intersections. Use these numbers as you plan your route to figure out how many total miles your trip will be. There are mileage charts in road atlases and other places, but they provide only a rough estimate of how far it is from one city to another. Those charts may not be a close enough approximation for estimating driving time.

As you're driving, you can monitor how you're doing by checking the mile markers. Mile markers are generally numbered from south to north and from west to east. For example, mile marker 1 on Interstate 90 is one mile east of the South Dakota-Minnesota border. The numbers then increase as you travel east from there. (Incidentally, mile markers are also used to determine exit numbers on Interstate highways.)

There are countless variables on a long trip though. You may add to the 50 mile per hour average if you are traveling with someone""that is, you can spend more time on the road because you'll always have a rested driver; there's no need to take long breaks to rest. Add another mile per hour or two if you plan on bringing a cooler full of food with you to avoid stopping for meals. If most of your trip can be on Interstate, that can add to your factor. The speed limit is higher, gas stations are more accessible, and Interstates are safer.

Of course, you'll have to at least take bathroom breaks. Bathroom breaks take about 10 minutes per person. Consider that guideline if you're traveling with a group of four or more, and especially if you're traveling with more than one vehicle.

Subtract from that 50 factor if you are traveling with kids. They always require more frequent and longer stops. Even an onboard dvd player will only keep them occupied for so long. They need to get out of the vehicle and exercise. If you are sightseeing rather than simply getting from point A to point B, subtract from the mile per hour average. There's nothing wrong with this""enjoy your trip. Just be aware that it adds to the overall time of the drive.

For example, traveling 1,800 miles alone I figured I could do in 36 hours. Traveling that distance with two people, we could probably average more like 53 miles per hour. I'd make that estimate about 34 hours. Traveling that distance with kids, you'll have to be way more flexible. And you'll likely have a better trip if you stay a night at a hotel. I'd say you'd average about 42 miles per hour, including stops. That would make an estimated driving time of 43 hours. Two nights or more at hotels would work best in this situation to break it up. But figure on 43 hours of on-the-road time.

Don't be too ambitious. Trying to average 65 miles per hour even with breaks is nearly impossible""and quite dangerous. The longer the trip, the more you need to stop and rest. You can drive through the night in order to get somewhere sooner, but you risk fatigue. The National Safety Council recommends stopping every 2 hours on long trips. Even with a break schedule like that, and even if you're in a hurry, you can still do better than 50 by taking food with you and taking short naps.

The Mapquest Web site is a good tool for obtaining decent driving directions and fairly accurate total mileage. But the estimated time does not factor in stops for meals, gas, breaks, sightseeing, or even mountainous roads, construction, or driving through some city's rush hour. The estimated driving time they give you is just that""time only spent actually on the road. Don't forget about other factors and variables.

I actually made it to Arizona by myself in a little under 34 hours. I had good weather and got lucky with road construction and timing of rush hours. I was also young and able to stay awake longer. Take it easy out there""don't try to overdo it.

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