I stumbled across this plan (http://www.lrta.org/london-Hounslow.html),
involving a tram from Hammersmith to Heathrow along the A4. They say
that it would reduce traffic on the A4 by 20%, however I understand it
would take up one lane in each direction (33%) of the road capacity,
therefore *increasing* congestion.

Which is simply wrong!

Normal car capacities (calculation guidelines values, real numbers are
significantly higher) are about 2000 cars/lane/hour.
Well let's say, that the cars have very high occupation (3 people per car,
which is way higher than the actual abt. 1,3) then we get a transport
capacity per lane per hour of 6000 persons per lane per hour.
A tram's capacity is abt. 22 thousand passengers per hour [1].
In the case of taking the car's value as their capaicity, it would still
reach only 10000persons/lane/hour.

Source [1]: Verkehrsclub Österreich (1999); Mobilität lernen - sicher und
umweltbewußt; Wien

regards
Tadej
--
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