Use I-405 HOT “Pilot Program” Results to Demonstrate Absurdity of Extensions

The WSDOT attempt to portray the results of the $484 million they spent initiating HOT on I-405 between Lynnwood and Bellevue as a boon to commuters is only the beginning.  They’re reportedly already planning to spend another $1 Billion extending HOT to Renton. 

The whole idea that HOT can reduce congestion for everyone is mathematically absurd.    If everyone is allowed to use GP lanes on a five-lane freeway, each lane can nominally accommodate 20% of the vehicles.  If, to encourage transit and carpoolers, one of the lanes is restricted to HOV that attracts 12% of the drivers, the percentage using each of the four GP lanes increases to 22%.   Thus HOV lanes benefit at the expense of a 10% increase in GP lane congestion.

HOT was purportedly initiated as the way to increase HOV lane velocities in response to legislation requiring they maintain 45 mph for 90% of the time by reducing the number of vehicles on the lane.    If HOV lane velocity with 12% of the vehicles is less than 45 mph, the number of HOV vehicles must be reduced by requiring +3HOV and setting HOT fees sufficient to do so.  If, for example, doing so requires reducing HOV to 8%, GP lane velocities presumably far slower with 22% of traffic will be slowed further with 23% of traffic.

The WSDOT, presumably attempting to generate more revenue and the probability of very high tolls needed to achieve 45 mph with a single HOT lane, initiated HOT on two lanes between Bothell and Bellevue where congestion is heaviest.  If the 45 mph edict requires limiting the HOT lane to 8%, two lanes could accommodate 16% of riders with lower HOT fees for each lane.  However, that requires each of the remaining 3 GP lanes accommodate 28% of traffic, three and a half times the congestion for those paying the HOT fees.  It’s no wonder 32,000 commuters have signed on to the “no tolls on I-405” agenda.

All of the above discussion was predicated on an assumption as to the percentage of vehicles a lane can accommodate and still maintain the 45 mph.   What’s needed is how does the actual number of vehicles affect the lane average velocity.   The $484 million, 2 year, I-405 HOT “Pilot Program” provides all sorts of data as to how HOV and GP velocities decrease with increasing number of vehicles and how HOT lane use (and tolls) increase with slower GP lane velocities. 

They should use that data to predict how allowing GP use on one of the two HOT lanes would affect average velocities between Bothell and Bellevue assuming half the HOT traffic switched to GP lanes.  At least in theory, the remaining HOT lane velocities would not change.   The WSDOT could use their data to show how the increased GP velocity would affect the number of those willing to use HOT lane, what the tolls would be, and the resulting average HOT velocities.   Fewer HOT vehicles will increase HOT velocity and decrease GP velocity and vice versa.  Both GP and HOT I-405 commuters surely have the right to know what allowing GP use of one of the HOT lanes would affect their commute.

One way to increase HOV velocities without increasing tolls would be to add P&R stalls with access to 10 BRT routes an hour during the peak commute.   (Way beyond ST3) Allowing 1000 commuters an hour to pay bus fare rather than HOT fees (and the savings from leaving their car near where they live rather than where they work) would undoubtedly reduce the HOT tolls needed to maintain some average HOV velocity.   The WSDOT could use the I-405 pilot data to predict HOV lane velocities and HOT fees with the added BRT routes.  They could also use the data to predict how future growth will affect the velocities with one or two HOT lanes.

The WSDOT needs to do a similar analysis before they decide to spend $1 billion extending HOT to Renton and whatever it takes to implement HOT on the new lane between Bothell and Lynnwood.   Again assuming an HOT lane requires limiting HOT lanes to 8% of the traffic requires the two GP lanes accommodate 84% of vehicles.   Increasing HOT lane users to 10 or 12% of vehicles would reduce HOT lane velocities but still require around 80% of commuters to use the two GP lanes.  While the WSDOT could use the “Pilot Program” average velocity results to predict HOT and GP lane velocities with the various splits between the two, common sense would “suggest” the GP lane velocities would be a debacle.

Unfortunately Rep Clibborn, the chairwomen of the House Transportation Committee, shows very little “common sense” when she insists they proceed with implementing the two HOT lanes on both extensions as a way to provide “the only unallocated source of revenue generated in the state”.   I-405 commuters will pay a very heavy price if she is allowed to prevail.