Posted Monday, September 19/05 in Driving efficiently

The Accord Hybrid technologies responsible for improvements of 8 mpg in the city and 7 mpg on the highway over the non-hybrid Accord:

(A) electric motor assist
(B) cylinder deactivation (3 cyl. mode)
(C) automatic engine shut off (idle-stop)
(D) improved aerodynamics

...result in these increases in fuel economy:

A. 57% of the highway mpg improvement (4.0 mpg of the 7 mpg increase)
B. 38% of the highway mpg improvement (2.65 of 7 mpg)
D. 05% of the highway mpg improvement (0.35 of 7 mpg)

A. 60% of the city improvement (4.8 of 8 mpg)
B. 15% of the city improvement (1.2 of 8 mpg)
C. 25% of the city improvement (2.0 of 8 mpg)

"So what! I drive a 15-year-old Metro!"

Well, unless your Metro is electric, there is one feature in the list of Honda technologies that applies to you. All gas Metros come factory-equipped with the idle-stop feature: the ignition key.

I regularly shut my engine off when it's not needed: railway crossings; lengthy red lights; traffic lineups; you name it. Crawling in traffic on a downhill grade? Guess what - my engine is probably off, while gravity pulls me along.

What about power steering and brakes when the motor is off? In a Metro, the steering is usually manual to begin with, so no big deal. And a vacuum reserve provides several assisted brake applications even after the engine stops. Besides, unassisted brakes in a car this light are manageable anyway.

I have read online (but can't find any evidence to back it up) that in some European countries, drivers beyond 2nd or 3rd in line at traffic lights are required to switch off. Certainly, anti-idling laws and campaigns are common in North America (where they apply to parked vehicles).

It's not practical to shut off as frequently as the computer-controlled Honda would - it would probably be hard on a "normal" starter (plus battery and charging system).

So a 2 mpg improvement in efficiency from a "manual" idle-stop system is likely out of reach. But it still shows that strategic use of the ignition key is bound to have a worthwhile effect on fuel economy.