The average crash frequency for a fifteen-mile stretch of 4-lane suburban undivided 

highway under base conditions (12-ft lanes, 6-ft shoulders, 55-mi/h freeflow

speed) may be estimated as:


The existing fifteen-mile segment, however, only has 11-ft lanes, 2-ft shoulders,

and a 45 mi/h free-flow speed. Local calibrations have determined that Crash

Modification Factors (CMFs) for the three non-standard conditions of the existing

site are:

It may be assumed that 90% of all crashes are affected by the lane width, shoulder

width, and free-flow speed conditions. It is proposed to upgrade the fifteen-mile segment to bring it to base conditions. What will be the observed crash frequency per year for the existing and proposed highway?

Assume that in both cases, 1.5% of all accidents are fatal, 5% involve disabling injuries, 10% involve evident injuries, and 2% involve possible injuries. Remaining accidents fall into the category of Property Damage Only (PDO). What will be the annual savings in crash costs due to the proposed improvements to the facility?