The City of Amarillo has had preventive maintenance programs, in one form or another, for many years. Available historical records clearly indicate the City has been Seal Coating paved streets for over 80 years. Some of the products have changed over the years, but the basic process of placing liquid asphalt and gravel onto the road surface as a preventive maintenance activity has not.
One thing that has definitely changed over the years is the quantity of streets that must be maintained:

Year Est. Population Area of City (Sq. Miles) Paved Streets (Miles)
1950 74,246 22.401 110.50
1961 138,000 54.78 382.94
1970 127,000 63.30 576.4
1980 157,180 81.40 699.95
1990 160,422 87.21 776.50
89.43 839.36
2010 194,527 100.24 911.12

Prior to 1990 the City’s seal coat program was touching every paved residential street and alley on a seven year cycle. Between 1990 and 2000 the cycle of seal coating was extended to eight years. Paved alleys were dropped from the seal coat program in 1998 and a new “alley seal” program was put in place. In 2002 the cycle was adjusted to ten years.
The cycle rate is determined by the amount of resources (materials, equipment and labor) available each year to cover the miles of paved streets in the city. The reason behind the cycle rate increases is due to the increase in miles of paved streets without a corresponding increase in resources.
In 2009 the Street Department began to use pre-coated gravel rock in the program. Reasons behind this decision are not only for aesthetics but it also reduces the amount of rock and liquid asphalt needed. Pre-coated gravel rock has reduced the total time involved. Using uncoated gravel rock required an additional week or two of sweeping to pick up the loose rock that did not bind.