Vertically Challenged
My scope of works in delivering the detailed design of two overtaking lanes (OTLs) in the middle of nowhere included identifying any show stoppers during a site walkover survey, which I did – twice.
Now that the design is well and truly underway, we have found that the vertical alignment does not meet the Austroads sight safety distances. So what? Well the Client stated the OTLs are to tie into the existing pavement which implies the vertical alignment is okay. Should I have identified this show-stopper? Impossible without a $20k survey.
What now? I rang the Client and told them what we had discovered. But they pay us for solutions, not problems. Understandably, they weren’t too chuffed with my solutions:
- Reduce the speed limit on the OTL to 80km/h. Yup. Genuine option.
- Regrade the zones to meet the safety standards. $$$$.
How could this happen? Well, the highway was built decades before the standards were published. Effectively, most of the highways in AUS could be sub-standard.
In my opinion, the Client is going to have to re-grade, or just accept the risk that someone might not see a 20cm high bunny rabbit from 210m away and just run it over. Easter is over-rated anyway.
Holdfast Training Services Trial Blog 
Daz, nice picture, did you get it from your kid’s Easter Cards this year?
how did you find out they don’t conform? Does Australia operate a system of departures from standard in the same way as UK? Did you have to tell the client?
Richard, we found out from the long section for the lanes. I have told the client and will be meeting them on Friday. The AGRD has an EDD (extended design domain). I spent the day going through that to see where I could apply common sense where conservative design was ruining me. It turns out increasing the deceleration coefficient because the highway is in a very dry region, and reducing reaction time by 0.5 secs takes the required SSD for a 0.2m object in the road from 210m to 139m. Further noting the 2.5m wide shoulders and 1.0m verges (all sealed), the allowable object height increases to 1.25m. I’m confident I’ll have a solution somewhere in the middle that communicates the risk the client will be accepting if they choose not to regrade.