WSDOT Compounds I-405 2-HOT Lane Debacle

As expected, the Seattle Times Oct 18^th Traffic Lab article, “State panel clears way for hikes in tolls for fast lanes” detailed the response to the request in an earlier Traffic Lab article.  That the WSDOT intended to eventually implement two toll lanes on I-405 between Lynnwood and Renton.  The problem is neither article acknowledges that the WSDOT plan to implement tolls on two lanes is more about increasing revenue than in reducing travel times.  

 

Tolls reduce multilane freeway travel times by maximizing the number of vehicles per hour (VPH) on one of the lanes they reduce traffic and travel times on the remaining lanes.  Studies have shown adjusting tolls to maintain 2000 VPH hour will maximize  traffic and assures 45 mph HOV lane speeds, minimizing GP lane congestion and travel time. 

 

Tolls avoid the problem when the number of carpoolers exceeds the 2000 VPH, slowing the HOV lanes. That off-peak operation limiting HOV to carpoolers wastes capacity that could be used to reduce GP lane congestion and travel time. During peak commute the WSDOT could raise tolls on one lane to whatever it takes to maintain 2000 VPH.  During off-peak they could lower tolls to attract more riders to maintain 2000 VPH and reduce congestion and travel times for all the freeway lanes.  

 

The WSDOT approach has been to use tolls to provide revenue.  For years they've imposed tolls on a second lane between Bothell and Bellevue that's increased congestion and travel times on the remaining  three GP lanes.  Then used the increased traffic and resulting congestion to justify cost of the tolls. Their plan to impose HOT on a second of four lanes for the rest of the route, taking away one of three GP lanes, is especially egregious.  Again, the  limited number of commuters willing to pay the fees reduces traffic on both HOT lanes below the 2000 VPH optimum; wasting capacity that could’ve been used to reduce GP lane traffic, congestion and travel time.  

 

The result has been less traffic raised HOV lane speeds higher than 45 mph but increased congestion and travel times on GP lanes.   The higher the tolls, the fewer those paying, the greater the GP congestion, and the longer their commute. 

 

The bottom line is adjusting the tolls to achieve the 2000 VPH on an HOV lane during both peak and off-peak operation is  an effective way to reduce GP lane congestion.  The WSDOT will rarely achieve that level if they impose HOT on two lanes, wasting that capacity. The Seattle Times Traffic Lab needs to recognize WSDOT plan to increase the tolls on the two lanes only compounds the debacle by reducing those willing to pay, increasing HOV velocity and GP lane travel time.