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If you've driven on Spanish roads recently, chances are you've rolled over one of those mysterious black cables stretched across the tarmac and wondered what on earth they're doing there. The devices, installed by Spain's traffic authority (DGT), have sparked plenty of speculation among drivers, particularly whether they're being used to catch speeders and dish out fines.

 

The short answer is no, they're not handing out penalties. But they are collecting quite a bit of information about your journey.

 

 

These pneumatic tubes have a straightforward job: measuring traffic density on the roads where they're installed. The hollow cables contain a sensor at one end and work through a simple mechanism that distributes air to the sides each time a vehicle passes over, effectively counting every car, van or lorry that crosses them.

 

The cables can distinguish between different types of vehicles based on their weight and number of wheels, which means the DGT can work out how many heavy goods vehicles are using a particular stretch of road compared to regular cars.

 

 

When the DGT places two cables consecutively across the road, they can actually calculate the speed vehicles are travelling. So technically, if they were fitted with cameras or other systems to identify which specific vehicle was speeding, they could function like a radar trap.

 

But the DGT insists they're not currently being used to issue fines, and there's no indication that's about to change.

 

 

The data collected by these black cables helps local authorities work out whether existing roads can cope with the volume of traffic they're carrying. If a particular stretch is constantly busy, it might need widening or could require a new dual carriageway to be built alongside it.

 

The information is also invaluable for understanding traffic patterns during specific times of the year, like bank holiday weekends or peak travel periods. By knowing when and where congestion is likely to build up, the authorities can plan ahead, manage traffic flow more effectively and put measures in place to improve safety during the busiest times.

 

Essentially, those unassuming black cables are helping Spain plan its road network for the future, even if they do look a bit suspicious when you're driving over them.

 

 

Image: Z22 via Wikimedia Commons