Why do many streets and sidewalks have a shine to them?

Two main ingredients create the shinning appearance of our concrete and asphalt roadway surfaces: natural rocks and glass. When it comes to asphalt and concrete, the contents are always hybrids, mixes of stones, sand, petroleum derivatives, and "fillers," ingredients that aren't necessary for the integrity of the pavement but provide bulk.
Sand, glass, silicon, and many natural stones, such as quartz, and all stones that glitter are sometimes used. Glass is included in roadways as a way of recycling used byproducts. Used tires are also sometimes thrown into the mix.
Road engineers are sensitive to the aesthetics of streets and sidewalks.
Portland cement, a mix made primarily of limestone and clay, becomes a particularly glittery surface when it bonds with sand and other filler agents to become concrete. Portland cement concrete becomes shinier and shinier as it is used. The aggregate on the very top of the street or sidewalk will lose part of its coating of concrete due to weathering and vehicular or pedestrain traffic. Once exposed, the light from the sun, headlights, street lights, or other sources bounces off the tiny surfaces of the aggregate, causing the streets and sidewalks to shine.
 http://en.wikipedia.org/wiki/Road_surface