One of the big touted benefits of driverless cars is the hoped-for reduction in highway congestion.

Sebastian Thrun in his landmark TED talk devoted significant time to talking about this very issue.

However Panos Prevedouros, writing for the Hawaii Reporter, states that based on current real-world research, these congestion reduction systems, otherwise known as ‘Automated Highway Systems’ face their own difficulties.

On a busy highway most drivers follow each other at a headway of about 1.5 seconds. As a result, the maximum sustained capacity of a freeway lane is 3600 seconds in one hour divided by 1.5 second headway equals 2400 vehicles per hour.

If car technology takes over, this headway can be reduced to 0.5 seconds which triples the capacity of the same freeway lane. So one lane could carry as many cars as an entire 3-lane section of the H-1 Freeway! This is clearly a bargain for our highway infrastructure.

However, if this was ever launched, it would require the presence of a largely empty lane next to the AHS lane (such as a bus-only lane with large gaps between the buses) so that vehicles can be merged in and out the tight AHS platoon; see the empty lane next to the platoon of fast moving Buicks in the picture above.) Only professional race drivers can routinely cope with 0.5 second headways (and they fail almost at every NASCAR race.)

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