RSAP Frequently Asked Questions
    Encroachment and Crash Rate Questions
Why are specific crash rates not being considered for the analysis?
RSAPv3 is calculating the crash rates.  The benefit-cost analysis is based on the crash rates that RSAPv3 calculates based on the Cooper Encroachment Rate model and the trajectories.
 
Is RSAP3 appropriate for analyzing alternative profiles or horizontal curves irrespective of roadside treatments? 
No.  While there are horizontal and vertical encroachment rate adjustment factors, RSAPv3 isnít meant to be a tool for analyzing alignments.  In fact, RSAPv3 requires that the alignment be the same for all the alternatives (i.e., only the roadside treatments are different).  If you are interested in how horizontal and vertical curvature affects the crash rates you should use the HSM or its computer program compliment in the IHSDM.
 
Where are the construction costs for each alternative entered?
Construction costs are entered at the top of the alternative worksheet.  The heading information for each alternative (i.e., the title of the alternative, the alternative number, etc) includes the construction and maintenance costs for that alternative.
 
Curious how the program is calculating predictive crash rates?  Using HSM?  Is the program using the Highway Safety Manual for predictive crash rates?  Or is this introducing another predictive model?  Which has precedent?
RSAPv3, like its predecessors RSAP 2.0.3, Roadside and BCAP, uses an encroachment modeling approach which is different than the crash frequency prediction approach used in the HSM.  It would not be possible to analyze the full range of scenarios that RSAPv3 can analyze with the HSM because you are limited by the types of CMFs available and the conditions under which those CMFs were developed.  There is research on-going to harmonize the RSAPv3 and HSM methods but for now the RSAPv3 method should be used to examine roadside situations and the HSM should be used to examine highway geometry and alignment issues.
 
What is the basis of the rate for accidents projected?
RSAPv3 uses the Cooper encroachment data and a statistical model of encroachments that is based on traffic volume, basic alignment , access density and highway type.  It is important to understand that this model is predicting encroachments rather than crashes.  Many encroachments do not result in crashes.  RSAPv3 takes the encroachments predicted and then uses a database of trajectories to see if the encroaching trajectory intersects any hazards on the roadside or in the median.