The Bellevue Reporter article on HOT
lane on I-405 prompted the following:’’
I was interested in the information the
WSDOT is spending $334 million to implement I-405 HOT lanes between Lynnwood
and Bellevue with the intent to spend an additional $1.1 billion extending them
to Renton. Presumable they
were doing so to generate additional funds and to alleviate congestion.
The ability to attract SOV drivers to
HOT obviously depends on the benefits from paying the surcharge. The benefits depend on the
percentage of total cars legally in the HOV lanes and the number of lanes on the
roadway. For example if a two-lane
roadway has one lane for HOV but only 10% of all the vehicles have more than one rider and therefore allowed to use it, the 10/90 split provides
a strong incentive to pay the surcharge.
If a third of the drivers do so the difference reduces to 40/60 and
dramatically improves overall traffic flow. However, there is little to be gained for additional riders
to pay extra.
For a three-lane highway the original
10/45/45 flow and 20% of the SOV drivers opt to pay the surcharge the resultant
split is 28/36/36. Its unlikely
additional SOV riders will pay the surcharge and the benefits to flow are reduced. Similarly with four lanes the initial 10/30/30/30 split, 10% paying the
surcharge gives a 19/27/27/27 distribution with little congestion benefit.
Its clear more lanes and more HOV riders
reduce not only the revenue from HOT but also the surcharge effect on
congestion. It isn’t clear what the WSDOT assumed
for the number of HOVs. With 20% HOV, an SOV
driver would benefit very little on a 4-lane highway. However, with 10% or fewer HOV drivers they should at least
consider simply doing away with the HOV lanes and use the $1.5 billion HOT funds
elsewhere.
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