Just returned from a weekend road trip to Monterey, CA. Was wondering on the return trip how accurate the ETA is and how complex the calculation is. I used the "Fast Route" for my trip home and had a major freeway (101 South) then a secondary hwy (Hwy 46 - two lane most of the way) then back to a major freeway (I5 South). I noticed when I made good time, the ETA would decrease by a few minutes and when making slow time it would increase by a few minutes. What variables does the nav system use to compute the ETA (arrival) time? Is it as simple as average speed x distance? Or, does it calculate such things as primary vs. secondary highways, or does it use the "Posted Limits" of the respective Hwys? Or perhaps it uses your current position by average speed.... Enquiring minds need to know

Also, I noticed the cruise control works as such: small tap on the lever will increase/decrease 1mph, a stronger push on the cruise lever will increase/decrease to the nearest 5mph then in 5mph increments from there. Another question...how come the AC system will not allow me to "split" the temps between passenger and driver? I start out in the (center knob) auto mode, then when my g-friend (who is always cold) tries to adjust the temp on the passenger knob - it doesn't seem to change her temp. We even pushed it's "auto" button (center of the passenger temp knob) and that didn't seem to change anything either.

Great road trip by the way and a pleasure to travel in the 535

 

Don't remember where I have this from, but I believe the Nav system has predetermined expected speeds for several road types (freeway, primary, secondary and city streets etc etc). It also keeps a record of the speed driven over the last 30 miles and presumably applies that to the "predetermined expected speed" to figure out the ETA.

The accuracy of the ETA is, IMHO, impressive.

The cruise control speed changes, as correctly described by you, is probably the best kept E60 secret.

 

Also being fascinated by the calculation, and being something of a numbers nerd I figured it out a while ago....

Scenario 1: Let's say Point A and Point B are on the same freeway, call it I-5 in CA which is where I live. Let's say you're going 80 mph and have been for a while. It assumes you will continue to travel at 80 mph until you get to your destination. This is pretty easy to verify by observation.

Scenario 2: Let's say Point A and Point B are on different freeways. In this case say you're on 405 in LA heading south (Point A). You're meeting I-5 and heading to San Diego (Point . If you're travelling 80 mph on 405 it assumes you'll continue at 80 mph only until you reach the intersection of I-5. Then on I-5 it assumes you'll travel at the speed limit the remainder of your trip. When you actually get to I-5 and you have travelled a few miles at 80 mph it'll adjust its time estimate because it now knows that you're travelling 80 mph instead of the speed limit. But it's funny - the NAV ETA won't assume the 80 mph you're doing on 405 will remain on I-5 until you "prove" it.

Each car manufacturer is different. Our other car (Acura) always ignores my my current speed when travelling above the speed limit. It assumes it's only temporary, and the ETA always assumes that from this moment forward I'm really travelling at the speed limit.

 

Interesting that BMW uses such a complex calculation and I agree - my ETA (for a 4.5 hour trip) was pretty much "dead on"! Pretty impressive

 

ref the nav calculation...

In-built, pre-configured speeds for the roads on the route. This is why you can plot a route whilst still parked on your driveway and then have an ETA without moving an inch.

System then dynamically recalculates the ETA at frequent intervals on the trip by assessing your position at each interval and then using its pre-configured speeds, it adjusts the ETA accordingly. Only time it "should" use your average travelling speed in the calculation is if you lose GPS signal for an extended period of time eg in a tunnel.

If it did not dynamically re calculate you would have scenarios where you arrived and the GPS still said you had X time remaining on your route or vice versa

Remember - it is constantly assessing your position against the route, this is why it only takes a few seconds to establish and re-route if you deviate.

(I know it uses a different mapping engine, but take a look at a TomTom - the settings allow you to change its pre-configured speeds which it uses for ETA calculations for each road type)