VDOT Put the Cart Before the Horse Heading Westbound on I-66 in the A.M.

On October 2, 2015 months after Virginia Department of Transportation (VDOT) announced its decision to toll I-66 inside the Beltway, it published the results of a modeling study entitled: “I66 Multimodal Improvements: Future Conditions Traffic Technical Memorandum”, which assesses the impacts of tolling on I-66 and parallel arteries.

Based on the Metropolitan Washington Council of Governments (MWCOG) TDM Version 2.3, Build 57 regional model, the report indicates that while traffic volume in the a.m. and p.m. peak [traditional] direction will not change much either on I-66 or parallel arteries, non-peak [reverse commute] direction traffic will divert onto parallel roadways. Traffic operations at key locations along Routes 50 and 29 will be degraded as a result.

These findings sound intuitively right. Peak direction traffic volume won’t be impacted because single occupancy vehicles (SOVs) diverting to and from the I-66 mainline will cancel each other out. Dynamic tolling will induce drivers to alter their commuting schedules, spreading traffic volume over a longer period and increasing road speed significantly. HOV drivers who can’t adjust their schedules and don’t want to pay the toll will seek transit options.

In the non-peak or reverse commute direction, that won’t happen, because for many of these drivers there is no viable transit option. Even with a Metro stop at Wiehle Reston, most reverse commuters have miles to walk or ride before reaching their destinations.

So far so good. The report is based on an authoritative source, it’s well illustrated and easy for laymen to understand. What’s not to like about it?

Instead of forming the basis for VDOT’s decision to toll or not to toll I-66, the report actually challenges the decision to toll by pointing up the intractability of reverse commutes. Nevertheless VDOT dismisses its own findings by concluding that reverse commute diversion will be minimal—even though traffic volume will increase by 50 percent at one location on Lee Highway and 70 percent at another (Table 2, p. 18).

My problem is not so much that VDOT’s conclusions obfuscate the report. My problem is why didn’t VDOT do the modeling study first, and then decide what to do about congestion on I-66 after? As things stand now, it has put the cart–tolling–before the horse–traffic impact analysis.


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