These projects keep highway pavements, bridges, bikeway facilities and associated items in a good condition. Examples are repaving a road to maintain ride quality, replacing deteriorated culverts, and repairing bridges. Preservation projects are normally given first priority preference. Many of these projects are developed from road inventories and inspections (e.g. culverts, guardrail, bridges, thermoplastic markings.) In 1986, the Division of Transportation implemented a computerized Pavement Management System (Argus) to target sections of roadway for preservation projects. Each fall, one-quarter of the system is tested on a four-year rotation—the test results are used by the software to develop an optimum set of recommended projects for the next five years, given budget availability.
Lake County has made a significant investment in its pavements; the estimated cost to build the existing county roadway network today exceeds $1.6 billion. Preservation projects help to protect this investment, and provide smooth pavements and bridges without load limits to highway users. On January 1, 2010 a change in Illinois law went into effect, increasing the maximum legal weight limit on local highways from 73,200 lbs. to 80,000 lbs. As truck weight inflict damage to pavements following a exponential curve rather than a linear curve, this change in truck weight limit is significant. It will operate to increase the required annual investment in pavement repairs, particularly if roads are allowed to become rough, which amplifies the effect of truck weights pounding on pavements.