Tuesday, 11 October 2011

Why PRT is not the answer

Another commonly suggested solution to the problems of our current cars is PRT (Personal Rapid Transit), where small rail vehicles offer direct journeys not shared with others. They are usually very light and can operate very frequently, so some think of it as being better for the environment and having more capacity than public transport beating it at its own game. However, I would disagree.
If a PRT vehicle comes every second (very optimistic), then 60 vehicles will come in a minute and 3600 per hour. Single occupancy in cars is normal, so if there is single occupancy in PRT that would be a paltry 3600 passengers per hour. Even with 6 per vehicle (PRT-pooling?), the capacity is 21 600 per hour. If a railway line has trains that carry 1000 people every 2.5 min 24 000 passengers can be carried in an hour, and more is possible. If trains for 1500 come every 2 min, 45 000 can be carried, in which case PRT vehicles would need to carry on average 12.5 people, even with a nearly impossible one min headway.
If PRT can be made lighter than trains, why can’t trains be made even lighter? In addition, PRT infrastructure on every street (necessary for it to be useful) would be very expensive.
In conclusion, while PRT could work in an expensive private community, it is not suitable for serious transport needs in large cities.

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