2014 Source Selection of Plug-In Hybrid

Source selection is a formal engineering process that compares different products against the requirements to identify the best candidates. Now I had already decided to go with a used 2014 for price which every candidate car meets. The only question remaining, requirements and capability.

For requirements, I used two families. The first is our older, two adults, no kids, with "stuff." The second a younger family with kids. With different requirements, their logical choices will vary.

For the capabilities, we used EPA and automotive reviews:

	metric\2014	BMW i3-REx	Accord plug-in	Chevy Volt	Prius plug-in
1	MPGe	117	115	98	95
2	seat belts	4	5	4	5
3	volume	99	112	108	116
4	0-60 mph	7	7.7	8.7	10.2
5	range	150	570	380	540
6	MPG	39	46	37	50

Since some metrics are better with low number and others with high numbers, we decided to use a linear scale, 1-worst and 4-best. A linear function is not always the best but good enough for our purposes:

	metric\score 4_best	BMW i3-REx	Accord plug-in	Chevy Volt	Prius plug-in
1	MPGe	4	3	2	1
2	seat belts	1	2	1	2
3	volume	1	3	2	4
4	0-60 mph	4	3	2	1
5	range	1	4	2	3
6	MPG	2	3	1	4

So the BMW i3-REx has the highest MPG3 and gets a "4". In contrast, the Prius plug-in has the worst MPGe and gets a "1". Of course a linear scale may not reflect true worth but that is beyond the scope of this example.

Having assigned objective quanties, 1 to 4, for each metric, we need to use the requirements weighting for each family. A non-linear percentage of merit is assigned to each metric. This is multiplied times the weight value to make a 'suitable for use' number. These are added up so the car with the highest number is the one best suited for that family. In this case, the empty nesters.

	metric\score 4_best	BMW i3-REx	Accord plug-in	Chevy Volt	Prius plug-in
1	Adults 2 + trailer	3.30	3.13	1.93	1.56
2	MPGe (55%)	2.20	1.65	1.10	0.55
3	seat belts (2%)	0.02	0.04	0.02	0.04
4	volume (3%)	0.03	0.09	0.06	0.12
5	0-60 mph (20%)	0.80	0.60	0.40	0.20
6	range (15%)	0.15	0.60	0.30	0.45
7	MPG (5%)	0.10	0.15	0.05	0.20

So by score, the "BMW i3-REx" is the best for this family followed by Accord plug-in, Chevy Volt, and Prius plug-in.

Doing the same analysis for the family of two and three kids:

	metric\score 4_best	BMW i3-REx	Accord plug-in	Chevy Volt	Prius plug-in
1	Adults 2 + kids 3	1.59	2.47	1.40	2.34
2	MPGe (15.0%)	0.60	0.45	0.30	0.15
3	seat belts (55.0%)	0.55	1.10	0.55	1.10
4	volume (20.0%)	0.20	0.60	0.40	0.80
5	0-60 mph (3.0%)	0.12	0.09	0.06	0.03
6	range (2.0%)	0.02	0.08	0.04	0.06
7	MPG (5.0%)	0.10	0.15	0.05	0.20

The Accord plug-in followed by the Prius plug-in are the leading candidates. The BMW i3-REx and Chevy Volt both trail badly because of the four seat belts meaning it could never carry everyone for a trip. In fact, the 4-seaters would have been eliminated as having 5-seats is a mandatory requirement. But I included them only for illustration of the approach.

Having spent tens of thousands of dollars on a ride tends to make one a 'fan boy' and sometimes they don't realize other families have different requirements. So this leads to endless bickering over which ride is best. Engineering doesn't care because it is requirements driven and hang the rest.

Bob Wilson

 

With the exception of 0-60 seconds, I used the EPA numbers including range for the 2014 models. My eyes see 380 miles for that model year. What were you expecting?

Bob Wilson

 

Old man eyes. I'll fix tonight. It is in a spreadsheet and manual data entry ... 'bout as good as my speellin. It is supposed to be total range.

I did not give high weighting for range so probably won't shift the order much. Now if someone were a sales critter or field service tech, it would have a higher ranking and a Level 2 ECO might be a better solution.

Bob Wilson