I’m working on a project where an unfavorable arrangement occurs where a Freeway entry ramp overlaps with a high speed 2 lane exit ramp. This obviously results in some very unsafe weaving manoeuvres to allow entry traffic to weave through traffic to try and join the Freeway. Because the risk factors for merge lanes are low even if I coding it as having poor quality the SRS is still low compared to road safety risks at this location. Are there any ways to code for this type of scenario that would better reflect the safety issues?
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Hi Paul, thanks for sharing this, it’s a scenario I see often too, where exits are a very short distance from entries to high speed roads. One suggestion could be to code this as a four leg intersection? That would create a spike in the risk score at fatality and injury estimations, flagging it as a location for treatment. (This isn’t an official guide from iRAP, just an idea!). Keen to hear what you and others think.
Thanks Greg, Changing the intersection type seems like the only option but I’m worried about the push back from the client. The main crash type I’m concerned about is rear-end collisions, so although the severity is higher than side-swipes they are still quite a bit lower than side-impacts. The severity factor for merges in 15 and for 4-leg intersections it is 45/50, which I assume is made up from rear-end and side-impact crashes. So maybe based on this the Mini Roundabout might be a good option, as its severity factor is 35, which is the next lowest after Merge Lanes and Roundabouts. Its still probably too high as it’s in a 100km/h speed zone, so I might have to also adjust the side-road traffic volumes.
Has AusRAP thought about an option where unique Likelihood/Severity factors could be entered by the coder based on a more detailed analysis of an intersection?
Hi Paul, yes i totally understand the challenges communicating this to your client, it’s an imperfect solution. The mini roundabout is a good option to look at. I’m going to share this thread with James, our Innovation and Development lead, because has been working with the Brits on a rear end module. The idea of user-defined factors is an interesting idea but it would have some challenges - like ensuring factors are evidence based and considering how it would effect the overal star rating standars.
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