Here's a few concepts I did for a t-shirt for a 5k walk/run. It was a fundraiser for LAMP for Haiti. They provide medical care for the people of Haiti and the race was to help fund their mobile out reach clinic/truck, hence the name "Truckin' for Haiti". They ended up picking a very different image. One that was a more literal take on Crumb's "Keep on Truckin" character. These however were my favorites. You can check out the image they chose on their website. While you are at it donate a few dollars. Every little bit helps and it's a great cause!
Keep on Truckin!