which would be better for MPG, staying on the highway driving 70+ mph for five miles or staying on the feeder road (runs next to highway) for the same 5 miles, driving 45 mph but having five traffic lights? time is not a factor
How easy is it to time the lights? Would doing 60MPH on the freeway be an option that wouldn't get you run off the road?
Air resistance goes up with the square of the speed. So you have well over twice the drag at 70+ mph than you do at 45 mph (70 squared divided by 45 squared is about 2.4). That suggests you're going to use up at least twice as much gas on the freeway compared with a nonstop trip on the slower road. So it boils down to how much fuel you waste stopping and starting at those traffic lights. Depending on the lights and timing, you might be expected to make it through half of them without stopping, so we're now down to only two or three stops / starts. The Prius C recovers much of its kinetic energy through the use of it's electric motor and regenerative braking, which is most effective at the slower speeds. Chances are you wouldn't loose much (if any) more energy from a couple of stops and starts to 45 mph than you would in the extra acceleration from 45 to 70mph that you'd need to use the freeway. Combine that with the decreased drag and my money's on the feeder road. Especially if you "drive ahead" and try to hit the lights when they're green.
thanks for the reply's, 60 mph is not an option or at least a safe one. I'll do a month of the feeder and see how it goes.
That was going to be my suggestion. You, and only you in your personal situation, will be able to adequately answer this question. Once you determine if the slower route is better (it should be), then you'll need to assess if it's worth the time. This is something that happened with me. Learning to drive hybrids for best mpg, I found a similar slower route on my daily commute that gave me much higher FE but it was longer, less comfortable (bumpy road) and took more concentration on my part to pulse and glide. Getting a plug-in allowed to drive "normally" over the faster route with much less driving "hassle".
Feeder at 45mph hands down. Note, you have two methods to try on that road but it depends on how the lights are timed. You DWL the entire section and hopefully you don't have to slow down too much for each of the lights. You do this by getting up to 70km/h (just under 44mph.. so let's say 43mph to be safe) and hold the accelerator such that your Hybrid System Indicator is only half filled (dark green bar only). If MG1 is disconnected, your instant FE gauge should be somewhere between 65 and 75mpg. If MG1 is engaged for whatever reason, the iFE gauge will be at 45-50mpg. Good but not the numbers you want to achieve. You use this method if there's traffic and you need to keep the speed up. Depending on the grade of the road, you may or may not lose speed but it shouldn't be much (1-2mph) You P&G the entire section (31mph-43mph or 50-70km/h) and time the glide such that the lights turn green when you need to accelerate (pulse) back up to speed.
