AutoP and Nav

* Plan your trip like a pilot
* Mountain driving strategies
* Autopilot Impressions


When I am asked, “What happens if you run out of battery power before you reach your destination,” I reply, “I’ve been flying for decades and have never run out of gas, why should I start coming up short now that I own an electric car?”

In other words, plan to never run out of battery power. To achieve this goal, you have some great tools at your disposal
* Plan to arrive  at your drive’s completion with an adequate reserve
* Monitor your energy use en route
* Understand the tools you have at your disposal to influence range
* Proceed to an alternate plan if your original plan is not working
Let’s look at each.

Arrive with an adequate reserve
Does Tesla force you to discontinue supercharging the moment you receive the message “you have enough energy to continue on your trip?” Of course not. You’re free to add a bit more energy before hitting the road, and that extra reserve can come in handy if your energy needs turn out to be greater than expected.

You’re also free to plan your trip in such a fashion that legs of the trip are within your range, given the speed you intend to drive.

For the most part, Tesla’s Navigation software does a good job of forecasting how much energy you’ll need to reach your destination with some reserve. Why accept a really skinny reserve when just a few more minutes of charging will give you a comfortable reserve? I normally like to arrive with about 50 miles reserve, but I will cut it down to even half that amount when circumstances dictate.

Monitor your energy use en route
This is huge. When I was a flight engineer on trans-Atlantic flights, the fuel information the captain wanted to know the most was how we’re doing compared to plan. If I said “1500 lbs to the good” and we stayed there, he’d be happy. On the other hand, if we were falling behind compared to our plan, maybe due to stronger-than-forecast headwinds, then he became concerned and started thinking of ways to either improve our range or he started considering Plan B in case we wouldn’t have enough fuel to make our planned destination with sufficient reserves.

On the Tesla, you have a really great tool for monitoring your trend. It is the percentage of range remaining at destination number available on the Tesla Navigation display. If you look at the bottom of your route display, there’s a button called “trip”. Push it and among other information you will see the percentage of energy remaining when you reach your destination or the next supercharger.


In the example above, on my leg to Alaska, the navigation software initially indicated that I’d have 10% of my energy left pulling into Hyder. That’s about 24 miles in a 240 mile range 70D, which is pretty skinny. I therefore needed to make sure that number grew or remained the same, but didn’t fall. Fortunately, throughout the trip I drove slowly, causing the number to grow until it was showing more than 20% as I neared my destination.

Sometimes this number will fall quite a bit during the first few minutes of your drive. The software needs to get a feel for your driving style (speed, etc.) and it will compute a more accurate number once you have traveled far enough.

If you don’t monitor your energy en route, then you may get the dreaded “Slow down to reach your destination” message from the Tesla navigation program. Your energy level is getting critical if you see this message, and you really do need to respond. Rather than getting yourself in a tough spot where you need to slow way down, however, why not simply monitor the trend and make small adjustments as necessary?

Range tools at your disposal
One simple bit of physics you need to understand when driving an electric car is that aerodynamic (parasitic) drag is a factor of the square of your speed through the air. In other words, if you double your speed on a calm day, the vehicle will now be generating 4 times the amount of aerodynamic drag as it did before. The bad news is that going fast burns lots of energy. The good news is that you have a GREAT tool to use for increasing your range when you are off the supercharger network or you are in a bind and need to stretch your range. All you need to do is slow down. I typically use about 279 watt-hours of energy per mile driving my Tesla 70D. If I am roaring along at 85 mph, I can consume more than 350 wh/mile, and if I’m poking along at 40 or 45 mph, I can sometimes burn less than 240 wh/mile. That’s a huge difference in energy burned per mile.

By monitoring your energy reserve at destination (see above), you can stay in the comfort zone throughout your trip. Consider, for example, a case where an unexpected wind starts blowing from the direction you’re driving. It will cut down on your range, but if you adjust your speed early, you should be able to stabilize your reserve energy at destination number. This approach sure beats getting the dreaded slow down message from the nav program and having to creep your way to your destination.

Environmental controls (heat, defrost, air-conditioning, etc.) use energy and must be considered when planning your trip. The Tesla battery will also sometimes require energy to heat it or cool it, and thus extreme temperatures either way can adversely affect range. By using less air conditioning or heat, you can extend your range if you find yourself in need of doing so.

Proceeding to your alternate
In a worst case situation when unexpected nasty-strong winds start blowing from the direction of your destination, temperatures plummet, or your road is closed and a major detour is needed, you may find yourself unable to reach your destination with an adequate reserve of energy. What to do? Follow the example of pilots, and proceed to an alternate destination to pick up more fuel and evaluate your next move. Fortunately, Plan B is quite easy in an electric vehicle. Virtually any RV Park can give you a quick resupply of energy, and in the worst-case scenario, any building with a standard electrical plug can give you energy as well. It won’t be quick, but it’s better than running out of electricity. All of this said, I’ve been driving for a month straight in extreme conditions sometimes, and I have yet to need to deviate substantially from my plan. Add in the increased reliability of  electric vehicles, and I believe I’m far less likely to be stranded in my Tesla than in a typical internal-combustion engine machine.


So, you’re driving from Sacramento up to Lake Tahoe, with a charging stop at the Truckee Supercharger. You’ve departed with 50 miles more energy than the 120 or so road miles to Truckee, and the funny thing is that your Tesla’s Navigation software says you don’t have enough energy to make Truckee. Should you believe it? In this case, yes.

Consider the following screenshot from a recent drive up to Donner Summit from the east side. Yep, I was averaging 634wh/mi. of energy use, more than double my average energy use on level terrain at 70 mph.

Running up I-80 to Donner Summit at 70mph, I exceeded 600wh/mi. energy usage

Ah, but you say you see the problem and will slow down and stretch your range climbing that mountain. Well, good luck, because you’re likely to get only about a 35wh/mi. improvement by reducing aerodynamic drag, and the resulting 600wh/mi energy consumption will gobble up your energy before you top the summit. Whether you cruise slowly or quickly, there’s still the work required to lift your more-than-2-ton car a mile into the atmosphere.

What to do? Believe the Tesla Navigation program when it tells you how much of a bare minimum charge is needed to reach Truckee (and then give yourself a bit more energy for “just in case” scenarios). Next, monitor your energy at destination by clicking on the “trip” button at regular intervals. Don’t wait for the Tesla Navigation Program’s “Slow down to reach your destination” warning.

Just how much of an energy difference is there between climbing the Sierras from abeam Rocklin (supercharger location) to Donner Summit and proceeding in the reverse direction? Consider these numbers:
* 75 miles- Approx. road miles, Rocklin turnoff to Donner Summit
* 125 miles- Approx # of Tesla miles of energy consumed from Rocklin to Donner Summit
*  25 miles- Approx # of Tesla miles of energy consumed from Donner Summit to Rocklin
(Note: Tesla energy miles set to EPA setting rather than “ideal” setting)

Now, let’s subject mountain driving to our Plan Your Trip Like a Pilot rules:
Arrive with an adequate reserve- You need to trust Tesla’s Navigation software when it gives you a large number of miles needed for covering the uphill route. Energy burn can be double the number you normally see for level driving. Then, add a larger than normal reserve (I like at least 50 miles) when traveling in the mountains due to greater need for contingencies.

Monitor your energy use en route– Push the “Trip” button on the Tesla Navigation software from time to time to see how your energy-at-destination number is looking.

Use the range tools at your disposal if you’re falling behind– Slow down or do some drafting to keep your reserve energy number looking good. Remember, though, that these tools can account for winds and fast cruising speeds but are insufficient to account for the climb itself.

Proceed to your alternate– If a public charging station or RV park exists, stop and get a helper charge. Otherwise, plan to turn around and head downhill to a charging station. The Donner Summit example shows that you can get as much as 5 times the range on the downhill run than on the climb to the summit.


Throughout the road trip, I used the speed control function of the autopilot, known as TACC (for Traffic Aware Cruise Control). It works beautifully. The car actually reads speed limit signs, displays these limits, and warns me if I’m exceeding limit +5 mph (the driver can control this setting). I found this feature to decrease the workload of driving. Instead of worrying about my speed, I set it at a speed that likely would never get me pulled over, and I allowed the car to adjust its speed as the car in front of me slowed or sped up. I was now able to spend more time focusing on the overall driving experience.

While I still had a couple trips to California planned, the Autopilot matured and AutoSteer became available. AutoSteer will keep the Tesla within your lane or change lanes for you if you put on the blinker and the adjacent lane is indeed clear. Naturally, I tried it within hours of the software download and was very impressed with the technology. Alas, on the winding mountain roads to and from California, I learned what AutoSteer is good at and what it needs more work on before I will trust it in those conditions. Remarkably, Tesla drivers started reporting that AutoSteer was improving by the day. One person who commutes on the same route each day reported 6 time he had to intervene, then 5 the next day, 4 the day after, and so on until within about a week the driver had noticed that AutoSteer had learned the highway and was performing properly! Elon Musk later confirmed that a learning function is incorporated in Tesla vehicles and that learning is shared with the entire Tesla fleet. Can’t wait to return to the mainland and give it another try.

Here’s a graphic I created to show what the autopilot display looks like and what each of the various icons and graphics means:


I used this graphic within a thread I started on the Tesla Motors Club forum entitled “A Flight Instructor Teaches Tesla Autopilot”. The parallels between aviation and Tesla’s autopilot implementation are significant, and so I wished to give Tesla owners an opportunity to see how a flight instructor would introduce this new piece of technology to a student. Over 1500 Tesla enthusiasts have viewed the thread.

What was my favorite autopilot moment? I was driving at the end of a long day and tired as I headed East on I-80 from Vacaville towards Auburn, CA. The highway here is well marked and lacks the steep turns of I-80’s mountainous region. The AutoSteer component of autopilot performed flawlessly and I was mighty grateful that my Tesla was sharing the driving chores with me this evening.

3 Responses to AutoP and Nav

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