# Why does Waze give a time estimate for this road trip two hours lower than Google Maps?

Google Maps: 13 hours, 5 minutes

Waze: 11 hours, 15 minutes

Pretty much the same path. Screenshots taken at the time, and both programs consider the traffic information.

What accounts for such a time estimate difference? Knowing this will help my scheduling.

• Isn't the Waze estimate an obvious bug? To drive 1366km in 11:15, you need to keep an average speed of 75.5mph. Doesn't the involved states Washington, Oregon and California all have a maximum speed limit of 70mph? Commented Aug 30, 2021 at 7:41
• @Tor-EinarJarnbjo maybe they look at the speed people actually drive at? Commented Aug 30, 2021 at 7:42
• This pretty much sums it up: mobile.twitter.com/tnose14/status/956301949921460225 Commented Aug 30, 2021 at 7:43
• @FranckDernoncourt It really depends on the state. Just match the speed of others, and know that the informal rules about what speed limits really mean change whenever you cross state borders. Commented Aug 30, 2021 at 13:08
• @AzorAhai-him- Most cars. Almost without exepection, car speedometers measure the rotation of the driveshaft and calculate an estimated speed by assuming a preconfigured wheel diameter. Depending on tyre wear and air pressure, the wheel diameter is however not a fixed constant. Since in most legislations speedometeres are only allowed to show a higher speed than the car is actually going, but never a lower speed, they are usually calibrated for a new tyre with the highest reasonable air pressure, meaning that in most situations, you are driving a bit slower than the speedometer actually shows. Commented Aug 30, 2021 at 21:01

It's simple.

Google Maps assumes that you are being a good driver and going no higher than the posted speed limit, and slower if necessary based on the speed of traffic.

When you input your destination into Google Maps your original estimate is made based upon posted speed limits, current traffic conditions, and the distance between your starting point and destination.

Waze does not take into account the speed limit and only looks at the speed of traffic. U.S. drivers tend to drive 15-20 mph over the speed limit on expressways (source - personal experience), and Waze assumes you will drive the speed of traffic. Note that driving over the speed limit is (obviously) illegal, so break the law at your own peril - it's not Waze's fault if you get a speeding ticket.

Here's an Medium article written by Waze themselves explaining how they compute travel time. Notice that the article does not mention speed limit as a factor.

I have taken long (4-5 hour) trips using Waze. I always drive the speed limit, which is often significantly slower than the speed of traffic, and I usually end up spending about 25% more time on the road than Waze predicts.

• Google also makes the reverse mistake--assuming the speed limit on roads where it's not possible to actually drive at that speed on parts of it. (The offender I noted was Titus Canyon Road. I reported it as a problem as it should never direct someone down that road but they have not fixed it. While the "limit" is 25 mph there are plenty of places on it that if you were driving 25 mph you would at best be in the hospital and more likely dead.) Commented Aug 31, 2021 at 3:41
• Looks like some rules are a bit outdated out there, with regards to modern standards for cars and constructions. Commented Aug 31, 2021 at 9:21
• @Yakk I can't imagine a road where the only safe approach was to speed. The road I'm referring to has a substantial chunk where it's one lane only (the entire road is one way), tight turns, if conditions were bad it would be 4x4 only and even in good times something like a sports car would probably end up high centered. Commented Aug 31, 2021 at 23:50
• Actually, that may be bad/old advice. The Arizona DOT now recommends pulling completely off the road (past the emergency lane/shoulder and on to the desert itself), stop your car, turn on/activate your emergency brake, take your foot/feet off the brake pedal, and finally turn off all lights. The bit about turning off lights and feet off brake pedal, is a history of people following other people's tail- or brake-lights and not realizing the car in front has stopped. Commented Sep 2, 2021 at 11:16
• @usr-local-ΕΨΗΕΛΩΝ I meant `under`, I was giving a rare example of needing to go above the speed limit. Commented Sep 2, 2021 at 13:44

Google Maps is "right" (only if no stops or traffic). Waze is wrong.

I've driven that exact route (Seattle to/from Bay Area via I-5) a couple dozen times. Only once did I manage 13 hours, and that was with only light traffic, literally no stops except for gas (2 brief stops), and consistently 5-10 MPH above the posted limit (which is what most of the rest of the cars were doing).

More typical is around 15-16 hours. That gives time for stretch breaks, stops for food, and possible traffic in the Seattle, Portland, and SF metro areas.

I have just noticed that Waze now has an option to personalize ETA based on past drives:

This may explain the difference with Google Maps. It's quite accurate at predicting my ETA in the US.