Train Icons for Gamification on "The Yelp for IT"

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This customer received 15 icon designs from 8 designers. They chose this icon design from SusanD as the winning design.
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The Wall Street Journal calls us "The Yelp for IT". On our site, users write reviews of enterprise tech products from companies such as IBM, Cisco, EMC, etc.
We are coming out with a new badge/gamification feature - the more reviews you write, the higher badge icon level you get. There are six levels:
Choo Choo Train (lowest level)
Caboose
Trolley
Commuter Rail
Train
Bullet Train (highest level)
You should create these 6 icons.
The icons should be no larger than 25px wide x 18px tall.
The colors/style should match our site: http://www.itcentralstation.com/products/quality-center
The badge icon would appear next to the "Real User" / Consultant badge for each user.
Target Market(s)
Enterprise technology buyers - conservative techies. This is not consumer, so be more conservative in the design.
Industry/Entity Type
Consultant
Look and feel
Each slider illustrates characteristics of the customer's brand and the style your logo design should communicate.