Monday, May 11, 2015

A little traffic, please?

When I would drive my gasoline powered cars, I would dread having to drive through congestion on the freeway.  Not only was I slowed by the traffic mess, but the car ran less efficiently, it was a little jerky on the frequent stop-starts, it was irritating listening to the engine idling or running at low speeds, and there were the exhaust fumes, from my car and the others around me.  And, in the summer, all those hot engines running seemed to make the freeway steam in the sun.  I always looked forward to the traffic break when I could again cut through the air at high speeds and the car was running near its peak efficiency.  So, why would I want to endure highway traffic congestion now?

Electric cars today lack a multi-gear transmission, which allows a gasoline engine to operate at both low and high speeds, while optimizing for the latter.  Generally, gasoline engines are rather inefficient at lower speeds, and they require a clutch mechanism in order to stop and resume, robbing the engine of its abundant power.  The electric car has just one speed, directly connected to the wheels because it can start turning from a stop.  Lacking other gears, the electric motor is less efficient at typical freeway speeds.  In short, the electric car can drive much further on the same amount of electricity at lower speeds (such as found in most highway traffic congestion).
My commute - 12 interstate miles and 7 expressway miles

Today was a case in point.  My drive to work consists of 12 miles driven at 55 to 60 MPH on the freeway, followed by 7 miles driven at 45 MPH on an expressway.  Lately, by the time I return home at the end of the day (38 miles late), the ninth (of sixteen) power bars in the charge gauge has disappeared.  Because of my work hours and meetings, I typically commute after much of the heavy traffic has subsided.  Today, however, was different.  I had to leave earlier for work and dealt with congestion along half of the freeway route to work.  I also drove home early and had to deal with a brush fire and two accidents along the way, which backed up traffic for nearly the entire stretch of the freeway I travel.  I also ran a few errands after arriving at home.  By the time that the charge gauge had dropped its ninth bar, I had driven 44 miles (or 15% farther).  So, I saved nearly 1.5KWh of charge by driving in congested traffic.

So, the efficiency is greatly improved in the slower moving traffic.  What about the other issues I face in congestion?  The interior noise in my car is dramatically reduced because there is no roaring engine (especially while idling).  Every start from a stop is delivered with silky smoothness thanks to the low-end torque available in an electric motor.  I am able to save a little time by using the carpool lane instead of being stuck with the rest of traffic.  And, of course, my car is not producing any exhaust gas fumes (and its electric charging is offset by solar power, both at home and at work).  If there were many more commuters also using electricity instead of gasoline, we’d all enjoy the drive home a lot better.

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