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31 The default values supplied with the State HCAS Model Bridge replacements resulting from structural deficien- are all based on the 1997 Federal HCAS. These data include: cies, and Load-related bridge repair and special bridge costs. VMT data by vehicle configuration and functional highway class; Minimum pavement thicknesses and the specification MAINTENANCE AND OTHER DATA of which state and coefficient option to use; Operating gross weight distributions by vehicle config- In addition to the travel and vehicle characteristic data and uration, and space for the user to specify different inputs required for pavement, bridge, and other costs in a weight distributions for selected highway classes or sound HCAS model, a carefully performed maintenance cost groups of highway classes; allocation procedure should require: Axle weight distributions for each vehicle configuration and operating gross weight group; and Expenditures for different categories of maintenance All other pavement data required by the State HCAS work, broken down by highway class: travel-related Model. maintenance, wear-related flexible pavement mainte- nance, wear-related rigid pavement maintenance, axle- The guidelines that accompany the model also contain related maintenance, truck-mile-related maintenance, advice for modifying the data for use in each state. light-vehicle-related maintenance, and possibly rest area maintenance; and BRIDGE DATA Specification of allocators for each of these cost cate- gories. A sound HCAS model should be designed to handle four bridge cost categories: new bridges, bridge replacement, Many states maintain detailed records of maintenance costs bridge repair, and possibly special bridge costs. An example by specific type of maintenance activity, such as pavement sur- of special bridge costs is the retrofitting of existing bridges face patching, joint and crack filling, culvert cleaning, bridge for earthquakes. painting, snow plowing, etc. These records also often include breakdowns of maintenance costs for specific routes or sec- The following additional inputs are typically required for tions of routes (e.g., by county or highway district). bridge cost allocation, all of which have default values pro- vided with the State HCAS Model: When such data are available, the user's primary task is to decide what allocation factors to use for each maintenance Assignment of vehicles to bridge increments based on activity or group of activities. An analyst doing a state HCAS their live-load moments, may want to consult the example contained in an appendix to An allocation of the cost of various types of new the guidelines for application of FHWA's State HCAS bridges to bridge increments, Model as a guide in preparing a similar table with that state's Information on the types of material and span lengths maintenance activities (Sydec 2000). for new and replacement bridges, Inventory ratings of bridges that are to be replaced, In the event that a state does not maintain detailed records An estimate of the percentage of bridge replacement of maintenance cost broken down by specific activity, the costs owing to structural deficiencies in existing user of the model should make estimates of breakdowns of bridges, maintenance expenditures by major class of activity through An estimate of the percentage of bridge repair costs that interviews with the maintenance managers who are responsi- are load-related, and ble for assigning work to crews. This may require meeting An estimate of the percentage of special bridge costs with managers in each district to fill out forms that break that are load-related. down known totals and/or subtotals of maintenance expendi- tures into the desired shares by major class of activity. Default values based on the 1997 Federal HCAS are pro- vided for the rest of the information required for the State A few states keep maintenance costs by functional class of HCAS Model. The guidelines provided with the State HCAS highway (or other highway classes that might be used in Model also provide detailed advice for handling each of the HCASs). However, more commonly there is a significant following operations: problem in converting costs to these highway classes. A fairly common problem is the need to convert costs by route or seg- Assignment of vehicles to bridge increments, ment of the route into costs by highway class. This typically Allocation of new bridge costs to bridge increments, involves building a conversion matrix, using the assumption Types of material and span lengths for new and re- that maintenance costs per lane-mile are constant, at least for placement bridges, each highway class. Average maintenance costs per lane- Inventory ratings of replaced bridges, mile for each highway class can be estimated from routes that