TRUCKS AND THEIR EFFECTS ON HIGHWAYS By WILLIAM T. SUNLEY, Illinois Department of Transportation

Public Act 83-12, which became effective on July 1, 1983, increased allowable truck size and weight limits in Illinois to conform with federal requirements. This Act increased the maximum truck size and weights allowed on Illinois highways as follows:
. increased the gross weight limit from 73,280 to 80,000 lbs.;
. increased the axle weight limit from 18,000 to 20,000 Ibs. and the tandem weight limit from 32,000 to 34,000 Ibs.;
. increased permissible vehicle width from 8 feet to 81/2 feet; removed the overall 60-foot length restriction;
. added a 21/2 cent diesel fuel differential;
. increased registration fees by creating two new heavy truck classifications -- 73,281 lbs. to 77,000 lbs., and 77,001 lbs. to 80,000 lbs.

Public Act 83-12 directed the Illinois Department of Transportation (IDOT) to study the impacts of the new size and weight limits on Illinois highways and the adequacy of associated fee increases, and report to the Governor and the General Assembly every three years. The first report on effects of larger and heavier vehicles estimated that accelerated deterioration of highway 'pavements would cost approximately $83 million per year. Newly available "Weigh-in Motion" data, while still very limited in application, indicates that damage estimates may be conservative. Heavier trucks are also contributing to a decrease in the service life of some older bridges on the state highway system. The Department estimates that the annual cost of this deterioration is approximately $9 million.

Segments of the trucking industry are receiving substantial benefits from the use of larger and heavier vehicles. The larger capacity allows the industry to meet demand with fewer vehicle miles of travel, which reduces operating costs. Total benefits are estimated to be about $450 million annually.

P.A. 83-12 also required the designation of a truck route system within the state on which the heavier and larger trucks may travel. Illinois currently has 11,036 miles on its system, which includes three classes of roadway. Class I roads are four-lane, divided and fully-controlled access highways, for the most part the Interstate System. Class II and III roads are typically two-lane U.S. and Illinois routes. The law sets out limits on the legal dimensions of trucks traveling on the designated system. The most important distinction is that only the heavier trucks, not the wider and longer vehicles, are allowed on Class III roads. P.A. 83-12 provides additional allowances for five miles of access to the designated system along other nondesignated state routes and for local designation of additional routes.

All discussion to this point has addressed the effect of P.A. 83-12 on roads under state jurisdiction. The local highway system is also being subjected to the stress of the higher legal loads. On June 1, 1991, the federal access provisions preempted any inconsistent state provisions. Access is automatically allowed within one road-mile of a Class I Designated Truck Route along local agency highways and five miles along state highways. The access route used must be the most reasonable and practical route between a Class I Designated Truck Route to points of loading and unloading and to facilities for food, fuel, repair and rest.

Access via a particular route may be prohibited for a specific safety reason (e.g. high accident locations or substandard geometries). If prohibited, a sign must be erected informing motorists that access is not allowed. Also, after FHWA approves our state access policy, any request for access beyond the one mile provision must be acted on within 90 days by the agency with jurisdiction over the roadway or it will automatically be allowed.

The last Motor Fuel Tax package included the 80,000 Ib. Truck Access Road Program which provide five million dollars per year for five years. The purpose of this program is to provide incentives to the local agencies to "beef-up" their road system to sustain heavier truck weights. These funds are administered by Local Roads through a local agency agreement with participation limits of $20,000 per lane mile and a flat fee of $10,000 per intersection. Since its inception in July 1989, the fund has obligated $8,999,400 on 79 projects. Any future projects considered for funding under this program should be discussed with your District Local Roads Engineer.

November 1991 / Illinois Municipal Review / Page 19