Improved, simplified routing input to RADTRAN

Recent changes have been made in the output from the HIGHWAY and INTERLINE routing programs which provide distance and corresponding weighted population density averages grouped within Rural, Suburban and Urban categories. These changes have made inputs to the LINK option of RADTRAN simpler and potentially more accurate due to reduced error-prone hand calculations. For analyses in which state-by-state accident rates may not be available, routes of any length can be treated with just three links: one each for the Rural, Suburban and Urban population-density average tabulated by HIGHWAY or INTERLINE. For analyses which involve state-by-state accident rates, simplification often results because the number of states traversed by a route is less than the number of highway intersections/changes. The latter subdivision of routes by HIGHWAY was employed in the past to define multiple links that permitted more detailed RADTRAN results for a particular route. However, if a single highway crossed two or more states, weighted-average accident rates had to be calculated for the three links describing it. Use of the new population-density tabulation in conjunction with state-by-state route subdivision eliminates this error-prone procedure