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. . . Drainage Drainage is accounted for on the surface and in the subsurface of the pavement section. It is extremely important to keep water from saturating and undermining the pavement and base. On the surface the pavement is sloped to get the water out of the roadway and into the storm sewer system. In addition surface cracks are sealed to keep water from draining into the pavement base through them. Typically a 12-inch sand layer is constructed beneath the aggregate base to add strength and to drain the base. In many cases perforated drainpipes are installed in the sand base to route any subsurface water in the pavement base to the storm sewer system. Because water is drained from the sand base the road becomes much less susceptible to freeze thaw cycles. The main causes for deterioration of bituminous pavement over its life span are the strength and stability of the pavement base, traffic volumes, type of traffic and environmental factors such as water, temperature, sun and pollutants. Traffic For design purposes traffic is estimated for the 20-year design life based on traffic counts and projected traffic growth rates averaged over the design life to determine the Average Daily Traffic counts for the roadway. In most cases MnDOT has traffic distribution tables for the perccntages of different vehicles that will be using the road. The traffic counts and the distribution of vehicles are used to calculate Equivalent 9-lOn (NI8) Single Axle Loads (ESALs.) The ESALs are used to determine both the base and surface thickness of the pavement section. For example, using ESALs, a typical garbage truck has the equivalent loading of approximately 1500 passenger cars. Although passenger cars are typically the largest percentage of vehicles to use the road the roadway section is designed to handle the loading of the larger vehicles. Tables H.l and H.2 from the MnDOT Geotechnical and Pavement Manual are included to show typical vehicle type distributions and the load factors applied to a particular type of vehicle. Environmental Water is very hard on the pavement section particularly in cities like Arden Hills where the clay soils under the road can trap water and become a problem during freeze thaw cycles. On pavement with no hard edges such as concrete curb and gutter the water can also contribute to the raveling of the pavement on the edges. The bituminous pavement itself becomes brittle over time from the effects of temperature, sun and pollutants. Typically most cracking exhibited in properly constructed bituminous roadways is due to temperature changes causing the pavement to expand and contract. For this reason, cracks are sealed and roadways are generally seal coated with a bituminous slurry and covered with a fine aggregate. Seal coating is typically recommend every 7 to 10 years to maintain and possibly extend the life of the pavement. It has been observed that many of the older streets in Arden Hills, particularly the rural design with no curb and gutter, rely more on the pavement as strength and do not have very good aggregate bases and generally do not have a sand layer. It is assumed that many of these streets began as gravel roads and have been overlaid with a bituminous surface with varying thickness.