LOSS for Bikes and Peds - Urban and Suburban Arterial SPFs

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LOSS for Bikes and Peds - Urban and Suburban Arterial SPFs

Postby benpdx » Tue Aug 05, 2014 1:59 pm


I'm using Level of Service of Safety (LOSS) to evaluate some sites where I've also used Part C predictive for urban and suburban arterials. My question is if it's valid to create two new LOSS scores for the bike crashes and for the ped crashes, separate from the SPFs for single-vehicle or multi-vehicle crashes.

Has anyone done this that could share some advice?

My concern is that LOSS requires the over-dispersion parameter (used to calculate the standard deviation) from the prediction SPF. It seems like for ped crashes at signalized intersections the process would be identical to vehicle crashes, since there is an SPF specific to that crash. However, for ped crashes at unsignalized intersections, the predicted number of ped crashes is derived just by multiplying the total number of predicted crashes by a pedestrian adjustment factor. I'm not sure how I would calculate the standard deviation (needed for LOSS) in this situation. Would it be just the pedestrian adjustment factor multiplied by the original standard deviation?

It's similar but slightly more confusing for bike crashes, which are derived by adding together predicted multi-vehicle crashes and single vehicle crashes (each of which have a dispersion factor / standard deviation), then applying a bike adjustment factor. In this case, there would need to be some sort of combined and factored standard deviation. Or alternatively, I could score bike LOSS using two separate scores, one for single veh bike crashes and one for multi-veh bike crashes. It might be hard to get that level of detail out of crash records though.

Any suggestions or comments are greatly welcome, I'd love to hear what other practitioners are doing.

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