Hampshire’s Ipley Cross is a notorious crossroads where cyclists keep getting hit and even killed by motorists, despite the mostly level terrain around the place where two roads cross each other at a seemingly innocuous angle.
But the crossroads have the bad luck to be at 69 degrees to each other, an angle that, when combined with the blind-spot created by the driver’s front pillar and a well-understood navigational hazard called “constant bearing, decreasing range” means that frequently, the first time a driver and a cyclist will see each other is a second or two before the car strikes the bicycle.
CBDR “is the phenomenon whereby two vessels, or vehicles, moving at steady speeds in straight lines towards a collision will maintain the same bearing” — and it’s well understood in aviation and nautical navigation, but is not taught to drivers, who are less prone to driving at a constant speed under normal road conditions.
Thanks to CBDR, a driver approaching the intersection at reasonably safe speeds of 37mph have a series of blind spots that coincide with the location of an oncoming cyclist traveling between 13.5mph and 17.5mph.
What’s more, the tricky angle at which the roads meet means that an oncoming car is continuously approaching the cyclist from behind, invisible unless the cyclist looks over their shoulder.
Drivers who move their heads significantly while approaching this seemingly wide-open crossroads can avoid this trap, but that’s hard to enforce. Alternately, the road engineers could put a kink in the highway that forces a stop and turn before proceeding through the junction.
“None of us are perfect drivers,” remarked Parekh’s defence barrister, attributing the whole affair to “human error”.The human error in this case, and the other cases, may have been for the drivers to have maintained a constant speed (as we know Parekh did) without having physically moved their head either side of the pillar to rigorously scan the area ahead and to their right.
There are two very simple solutions to the very real risk of a driver-vs-cyclist CBDR collision.Firstly, by slowing down significantly, any vehicle approaching from the right at a constant speed will move out of the obscured area and into view at the right of the windscreen.
And secondly, significant movement of the head will bring previously obscured sections of road into view.
It’s quite plausible that these simple strategies—either of them—could have prevented two fatalities at this one junction.
One of those strategies can, however, be easily enforced.
Why This Type Of Road Junction Will Keep Killing Cyclists [Bez/Single Track World]
(via Kottke)