Using only Star Rating Score to determine safety improvements

I have a general question that I hope someone on the forum has come up with a solution to. I have been asked on a few road design projects to calculate the SRS on an existing road and then on a proposed upgrade design. The idea is to improve the SRS as the design develops. The issue I have is that some of these projects are on highly congested road networks where there is a large difference between the operating speed and the mean speed, as much as 30km/h. The proposed design upgrades improved the SRS, but this SRS does not take into consideration the increase in the mean speed, which is used in determining the fatality estimates. The proposed design upgrades has improved traffic flow and increased the mean speed, by as much as 10-15km/h. So although the proposed design has improved the SRS slightly it has potentially increased fatality estimates. Ultimately to improve road safety we need to reduce fatalities and serous injuries and so a Star Rating based on the operating speed is not an indication that a proposed upgrade will reduce FSI crashes. I hope this makes sense and there are a few ideas within the constraints of the iRAP manuals to help better measure road safety with just a SRS.

Have you ever tried to take a look on the course HOW TO ACHIEVE STAR RATING SCORE? This one can be usefull in making sure that every improvement that is being done to the road, dows not affect any group of road users

Hi msangirs, yes I have reviewed/done all the courses iRAP have on the subject and I’m over all the possible road improvements for each road user. What I’m trying to determine is the best way to use only the Star Rating Score to determine how well a proposed design improves road safety. The ideal solution would be to undertake fatality estimates on the proposed design and compare it to the existing, but this is not an option at the moment. The issue as I understand it is that it is possible to have a reduction in the SRS (which uses operational speed) but an increase in fatality estimate (which uses mean speed). The reason is that if you have a very congested road and the proposed design improves the traffic flow the mean speed could jump by 10 - 20 km/h. The increase in mean speed could then offset the improvements used to achieve a lower SRS. I hope this helps to better explain the issue.