After I bought my car in L.A., I drove it back home to San Francisco. Half-way through the drive I looked at the trip meter, which I had reset before I left the dealership, and the average speed made no sense, it was way too low. If I took the miles on the trip meter and divided by the average speed, I got something like 9 hours, but I had only been driving for 5 hours, so obviously my average speed wasn't that low. Then just this week a friend of mine also bought a 2012 Prius, and he also noticed on his drive home that the average speed on the trip meter seemed way too low. Has anyone else noticed this? As far as I can tell, the miles driven and the MPG on the trip meters seem accurate, but the average speed doesn't make any sense.
Keep in mind idle time affects the average speed. So sitting there with the car turned on just to play with the controls counts in the average speed. Haven't taken a pure road trip as of yet; but will post my results when I do.
I made a similar trip from Carson to Sacramento and my average speed was accurate. I drove approx. 50 miles around LA then 420+ miles on I-5 at 70mph. The average speed read 59mph which seems correct given my stops, slow downs and accelerations. This is similar to what I've tracked in my GenII over the years using a Scangauge II. Yesterday I was holding steady at 45mph average and then I parked and left the car running for 45min or so. I later noticed my average mph had dropped to 39mph. I had started driving more rural roads later on that tank but I think sitting idle for so long is what dropped average mph so much.
Best way to check it is to get up to freeway speed then reset one of the trip indicators, then check it before you slow down. You will probably find, as I have, that it is pretty close. Your average speed around town, waiting for red lights, slowing for other cars, etc seems slow because it is slow.
Did you fill it up, reset the trip meter, and immediately hit the freeway and maintain freeway speeds the entire trip home? If you didn't reset the trip meter, you will have all the other "hours" spent by people doing test drives, leaving the car in READY mode while they tinker around with the radio, buttons, etc in the car. If you had any surface driving or stop and go traffic on your way home, that will impact your avg speed as well. Think about your daily commute. Most people think they drive 95% highway, when in fact it is much less than that. Mine is about 80% highway, but I also am "treated" to about 3-4 miles of slow and go traffic each way (more like 5 - 6 miles on the way home) on my ~35 mile one way commute. But it is 80% highway, so you'd think I'd be close to 50 mph. But when you add in the surface streets, red lights, slow and go traffic, my average mph is 35 - 40 mph. Which fits, as it takes me about 50 minutes to drive into work in the morning and 1 hour to get home. 70 miles/110 minutes = 38 mph.
Except in my case where I live less than 1 mile from the freeway and work less than .5 from the freeway (47miles total one-way). On days where I just commute my average speed is about 55mph (60-65mph freeway speed). On days where I do some in town or rural road driving it drops to 49mph or so.
We have done a few tests in the UK with the Prius display vs GPS and the average speed on the Prius trip meter is pretty close to GPS. Idle time does count and a few minutes at 0mph will make a big difference to average speed. Also, the Prius speedo shows a higher mph than actual, so doing the 'keep a constant speed on the freeway and reset the trip' test will show average as less than the speedo (you could infer that average speed uses real mph and the speedo has a safety factor applied so you go slower than you think) Have fun.
The time when I -know- it was wrong was when I drove from LA home to San Francisco. Like I said earlier, part-way through the drive I looked at it, and divided the number of miles I had driven (around 300) by the average speed (something like 35 MPH), and just going back in time that number of hours, to have that average speed I would have had to start driving at a time in the morning that was earlier than I even arrived at the dealership, much less started driving. Also, the car only had 2 miles on the odometer when I got it, so, there was -maybe- one test drive. But, I guess I must not have reset the trip meter before starting like I thought I did, and somehow the car must have racked up a bunch of time with the ignition on and people playing with the gauges and stereo and nav without moving. So, thanks for the replies! The fact that no one else has had a problem leads me to believe that I just didn't reset it before hitting the road, and it must have been some time with the ignition on and the car parked that lowered the average speed.
