Why do you spread tar and stone on roads that are already paved?

The process you are referring to is called sealcoating or chip sealing. Most road agencies in Michigan use this process as a relatively low cost method of preserving existing pavement. 

The tar is an emulsion of water and liquid asphalt that penetrates and seals the smaller cracks in the existing pavement. Sealing these cracks on a regular basis prevents water from seeping into and softening the base of the road over time, which would cause potholes to form. The crushed stone that is used for cover material sticks to the emulsion and, after rolling and sweeping, provides a slightly roughened skid resistant surface which improves safety. 

Although sealcoating can preserve and extend the life of the pavement, it is only a surface treatment and does not fill any existing bumps, holes, or other irregularities and thus does not improve the ride quality. For this reason it is important to apply sealcoat to a road before deterioration occurs, which means we sealcoat roads that are in good condition rather than waiting for them to deteriorate to the point that extensive patching or reconstruction is necessary.

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1. Where does the Road Commission get its operating funds?
2. Why do you spread tar and stone on roads that are already paved?
3. Why is my road not plowed right away when it snows?
4. Your truck knocked down my mailbox - when are you going to fix it?
5. Why are there rules about the types of mailboxes and posts people can have?
6. My vehicle was damaged due to the condition of a road - is the Road Commission going to pay for it?
7. Where can I get information on current Travel information in Michigan?
8. Why are some roads numbered differently than others?
9. Is the Monroe County Road Commission responsible for state highways?
10. What are weight restrictions?
11. People are speeding on our road. How do I get the speed limit lowered?
12. My neighbors and I think we should have a traffic light at our corner. If I get enough signatures, can we have one?
13. I want to plant some trees along the road. Is that OK?
14. Do I need to get a permit to put in a new driveway?
15. I live on a gravel road, and I can't leave my windows open because of the dust - what are you going to do about it?
16. The gravel road I live on is full of holes - when are you going to grade it?
17. What causes potholes?